LAN Switching Configuration Guide, Cisco IOS XE Everest 16.6
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This module provides an overview of VLANs. It describes the encapsulation protocols used for routing between VLANs and provides
some basic information about designing VLANs. This module contains tasks for configuring routing between VLANS.
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Information About Routing Between VLANs
Virtual Local Area Network Definition
A virtual local area network (VLAN) is a switched network that is logically segmented on an organizational basis, by functions,
project teams, or applications rather than on a physical or geographical basis. For example, all workstations and servers
used by a particular workgroup team can be connected to the same VLAN, regardless of their physical connections to the network
or the fact that they might be intermingled with other teams. Reconfiguration of the network can be done through software
rather than by physically unplugging and moving devices or wires.
A VLAN can be thought of as a broadcast domain that exists within a defined set of switches. A VLAN consists of a number
of end systems, either hosts or network equipment (such as bridges and routers), connected by a single bridging domain. The
bridging domain is supported on various pieces of network equipment; for example, LAN switches that operate bridging protocols
between them with a separate bridge group for each VLAN.
VLANs are created to provide the segmentation services traditionally provided by routers in LAN configurations. VLANs address
scalability, security, and network management. Routers in VLAN topologies provide broadcast filtering, security, address summarization,
and traffic flow management. None of the switches within the defined group will bridge any frames, not even broadcast frames,
between two VLANs. Several key issues described in the following sections need to be considered when designing and building
switched LAN internetworks:
LAN Segmentation
VLANs allow logical network topologies to overlay the physical switched
infrastructure such that any arbitrary collection of LAN ports can be combined
into an autonomous user group or community of interest. The technology
logically segments the network into separate Layer 2 broadcast domains whereby
packets are switched between ports designated to be within the same VLAN. By
containing traffic originating on a particular LAN only to other LANs in the
same VLAN, switched virtual networks avoid wasting bandwidth, a drawback
inherent to traditional bridged and switched networks in which packets are
often forwarded to LANs with no need for them. Implementation of VLANs also
improves scalability, particularly in LAN environments that support broadcast-
or multicast-intensive protocols and applications that flood packets throughout
the network.
The figure below illustrates the difference between traditional
physical LAN segmentation and logical VLAN segmentation.
Figure 1. LAN Segmentation and VLAN Segmentation
Security
VLANs improve security by isolating groups. High-security users can be grouped into a VLAN, possibly on the same physical
segment, and no users outside that VLAN can communicate with them.
Broadcast Control
Just as switches isolate collision domains for attached hosts and only forward appropriate traffic out a particular port,
VLANs provide complete isolation between VLANs. A VLAN is a bridging domain, and all broadcast and multicast traffic is contained
within it.
VLAN Performance
The logical grouping of users allows an accounting group to make intensive use of a networked accounting system assigned to
a VLAN that contains just that accounting group and its servers. That group’s work will not affect other users. The VLAN configuration
improves general network performance by not slowing down other users sharing the network.
Network Management
The logical grouping of users allows easier network management. It is not necessary to pull cables to move a user from one
network to another. Adds, moves, and changes are achieved by configuring a port into the appropriate VLAN.
Network Monitoring Using SNMP
SNMP support has been added to provide mib-2 interfaces sparse table support for Fast Ethernet subinterfaces. Monitor your
VLAN subinterface using the
show vlans EXEC command. For more information on configuring SNMP on your Cisco network device or enabling an SNMP agent for remote
access, see the “Configuring SNMP Support” module in the
Cisco IOS Network Management Configuration Guide .
Communication Between VLANs
Communication between VLANs is accomplished through routing, and the traditional security and filtering functions of the router
can be used. Cisco IOS software provides network services such as security filtering, quality of service (QoS), and accounting
on a per-VLAN basis. As switched networks evolve to distributed VLANs, Cisco IOS software provides key inter-VLAN communications
and allows the network to scale.
Before Cisco IOS Release 12.2, Cisco IOS support for interfaces that have 802.1Q encapsulation configured is IP, IP multicast,
and IPX routing between respective VLANs represented as subinterfaces on a link. New functionality has been added in IEEE
802.1Q support for bridging on those interfaces and the capability to configure and use integrated routing and bridging (IRB).
Relaying Function
The relaying function level, as displayed in the figure below, is the
lowest level in the architectural model described in the IEEE 802.1Q standard
and presents three types of rules:
Ingress rules--Rules
relevant to the classification of received frames belonging to a VLAN.
Forwarding rules between
ports--Rules decide whether to filter or forward the frame.
Egress rules (output of
frames from the switch)--Rules decide if the frame must be sent tagged or
untagged.
Figure 2. Relaying Function
The Tagging Scheme
The figure below shows the tagging scheme proposed by the 802.3ac
standard, that is, the addition of the four octets after the source MAC
address. Their presence is indicated by a particular value of the EtherType
field (called TPID), which has been fixed to be equal to 0x8100. When a frame
has the EtherType equal to 0x8100, this frame carries the tag IEEE
802.1Q/802.1p. The tag is stored in the following two octets and it contains 3
bits of user priority, 1 bit of Canonical Format Identifier (CFI), and 12 bits
of VLAN ID (VID). The 3 bits of user priority are used by the 802.1p standard;
the CFI is used for compatibility reasons between Ethernet-type networks and
Token Ring-type networks. The VID is the identification of the VLAN, which is
basically used by the 802.1Q standard; being on 12 bits, it allows the
identification of 4096 VLANs.
After the two octets of TPID and the two octets of the Tag Control
Information field there are two octets that originally would have been located
after the Source Address field where there is the TPID. They contain either the
MAC length in the case of IEEE 802.3 or the EtherType in the case of Ethernet
version 2.
Figure 3. Tagging Scheme
The EtherType and VLAN ID are inserted after the MAC source address,
but before the original Ethertype/Length or Logical Link Control (LLC). The
1-bit CFI included a T-R Encapsulation bit so that Token Ring frames can be
carried across Ethernet backbones without using 802.1H translation.
Frame Control Sequence Recomputation
The figure below shows how adding a tag in a frame recomputes the Frame
Control Sequence. 802.1p and 802.1Q share the same tag.
Figure 4. Adding a Tag Recomputes the Frame Control Sequence
Native VLAN
Each physical port has a parameter called PVID. Every 802.1Q port is
assigned a PVID value that is of its native VLAN ID (default is VLAN 1). All
untagged frames are assigned to the LAN specified in the PVID parameter. When a
tagged frame is received by a port, the tag is respected. If the frame is
untagged, the value contained in the PVID is considered as a tag. Because the
frame is untagged and the PVID is tagged to allow the coexistence, as shown in
the figure below, on the same pieces of cable of VLAN-aware bridge/stations and
of VLAN-unaware bridges/stations. Consider, for example, the two stations
connected to the central trunk link in the lower part of the figure below. They
are VLAN-unaware and they will be associated to the VLAN C, because the PVIDs
of the VLAN-aware bridges are equal to VLAN C. Because the VLAN-unaware
stations will send only untagged frames, when the VLAN-aware bridge devices
receive these untagged frames they will assign them to VLAN C.
Figure 5. Native VLAN
PVST+
PVST+ provides support for 802.1Q trunks and the mapping of multiple spanning trees to the single spanning tree of 802.1Q
switches.
The PVST+ architecture distinguishes three types of regions:
A PVST region
A PVST+ region
A MST region
Each region consists of a homogenous type of switch. A PVST region can be connected to a PVST+ region by connecting two ISL
ports. Similarly, a PVST+ region can be connected to an MST region by connecting two 802.1Q ports.
At the boundary between a PVST region and a PVST+ region the mapping of spanning trees is one-to-one. At the boundary between
a MST region and a PVST+ region, the ST in the MST region maps to one PVST in the PVST+ region. The one it maps to is called
the common spanning tree (CST). The default CST is the PVST of VLAN 1 (Native VLAN).
All PVSTs, except for the CST, are tunneled through the MST region. Tunneling means that bridge protocol data units (BPDUs)
are flooded through the MST region along the single spanning tree present in the MST region.
Ingress and Egress Rules
The BPDU transmission on the 802.1Q port of a PVST+ router will be implemented in compliance with the following rules:
The CST BPDU (of VLAN 1, by default) is sent to the IEEE address.
All the other BPDUs are sent to Shared Spanning Tree Protocol (SSTP)-Address and encapsulated with Logical Link Control-Subnetwork
Access Protocol (LLC-SNAP) header.
The BPDU of the CST and BPDU of the VLAN equal to the PVID of the 802.1Q trunk are sent untagged.
All other BPDUs are sent tagged with the VLAN ID.
The CST BPDU is also sent to the SSTP address.
Each SSTP-addressed BPDU is also tailed by a Tag-Length-Value for the PVID checking.
The BPDU reception on the 802.1Q port of a PVST+ router will follow these rules:
All untagged IEEE addressed BPDUs must be received on the PVID of the 802.1Q port.
The IEEE addressed BPDUs whose VLAN ID matches the Native VLAN are processed by CST.
All the other IEEE addressed BPDUs whose VLAN ID does not match the Native VLAN and whose port type is not of 802.1Q are processed
by the spanning tree of that particular VLAN ID.
The SSTP addressed BPDU whose VLAN ID is not equal to the TLV are dropped and the ports are blocked for inconsistency.
All the other SSTP addressed BPDUs whose VLAN ID is not equal to the Native VLAN are processed by the spanning tree of that
particular VLAN ID.
The SSTP addressed BPDUs whose VLAN ID is equal to the Native VLAN are dropped. It is used for consistency checking.
Integrated Routing and Bridging
IRB enables a user to route a given protocol between routed interfaces and bridge groups or route a given protocol between
the bridge groups. Integrated routing and bridging is supported on the following protocols:
IP
IPX
AppleTalk
VLAN Colors
VLAN switching is accomplished through frame tagging
where traffic originating and contained within a particular virtual topology carries a unique VLAN ID as it traverses a common
backbone or trunk link. The VLAN ID enables VLAN switching devices to make intelligent forwarding decisions based on the embedded
VLAN ID. Each VLAN is differentiated by a color
, or VLAN identifier. The unique VLAN ID determines the frame coloring
for the VLAN. Packets originating and contained within a particular VLAN carry the identifier that uniquely defines that VLAN
(by the VLAN ID).
The VLAN ID allows VLAN switches and routers to selectively forward packets to ports with the same VLAN ID. The switch that
receives the frame from the source station inserts the VLAN ID and the packet is switched onto the shared backbone network.
When the frame exits the switched LAN, a switch strips the header and forwards the frame to interfaces that match the VLAN
color. If you are using a Cisco network management product such as VlanDirector, you can actually color code the VLANs and
monitor VLAN graphically.
Implementing VLANS
Network managers can logically group networks that span all major topologies, including high-speed technologies such as, ATM,
FDDI, and Fast Ethernet. By creating virtual LANs, system and network administrators can control traffic patterns and react
quickly to relocations and keep up with constant changes in the network due to moving requirements and node relocation just
by changing the VLAN member list in the router configuration. They can add, remove, or move devices or make other changes
to network configuration using software to make the changes.
Issues regarding creating VLANs should have been addressed when you developed your network design. Issues to consider include
the following:
Scalability
Performance improvements
Security
Network additions, moves, and changes
Communication Between VLANs
Cisco IOS software provides full-feature routing at Layer 3 and translation at Layer 2 between VLANs. Five different protocols
are available for routing between VLANs:
All five of these technologies are based on OSI Layer 2 bridge multiplexing mechanisms.
Inter-Switch Link Protocol
The Inter-Switch Link (ISL) protocol is used to interconnect two VLAN-capable Ethernet, Fast Ethernet, or Gigabit Ethernet
devices, such as the Catalyst 3000 or 5000 switches and Cisco 7500 routers. The ISL protocol is a packet-tagging protocol
that contains a standard Ethernet frame and the VLAN information associated with that frame. The packets on the ISL link contain
a standard Ethernet, FDDI, or Token Ring frame and the VLAN information associated with that frame. ISL is currently supported
only over Fast Ethernet links, but a single ISL link, or trunk, can carry different protocols from multiple VLANs.
Procedures for configuring ISL and Token Ring ISL (TRISL) features are provided in the Configuring Routing Between VLANs
with Inter-Switch Link Encapsulation section.
IEEE 802.10 Protocol
The IEEE 802.10 protocol provides connectivity between VLANs. Originally developed to address the growing need for security
within shared LAN/MAN environments, it incorporates authentication and encryption techniques to ensure data confidentiality
and integrity throughout the network. Additionally, by functioning at Layer 2, it is well suited to high-throughput, low-latency
switching environments. The IEEE 802.10 protocol can run over any LAN or HDLC serial interface.
Procedures for configuring routing between VLANs with IEEE 802.10 encapsulation are provided in the Configuring Routing Between
VLANs with IEEE 802.10 section.
IEEE 802.1Q Protocol
The IEEE 802.1Q protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. Cisco currently
supports IEEE 802.1Q for Fast Ethernet and Gigabit Ethernet interfaces.
Note
Cisco does not support IEEE 802.1Q encapsulation for Ethernet interfaces.
Procedures for configuring routing between VLANs with IEEE 802.1Q encapsulation are provided in the Configuring Routing Between
VLANs with IEEE 802.1Q Encapsulation.
ATM LANE Protocol
The ATM LAN Emulation (LANE) protocol provides a way for legacy LAN users to take advantage of ATM benefits without requiring
modifications to end-station hardware or software. LANE emulates a broadcast environment like IEEE 802.3 Ethernet on top of
an ATM network that is a point-to-point environment.
LANE makes ATM function like a LAN. LANE allows standard LAN drivers like NDIS and ODI to be used. The virtual LAN is transparent
to applications. Applications can use normal LAN functions without the underlying complexities of the ATM implementation.
For example, a station can send broadcasts and multicasts, even though ATM is defined as a point-to-point technology and does
not support any-to-any services.
To accomplish this, special low-level software is implemented on an ATM client workstation, called the LAN Emulation Client
(LEC). The client software communicates with a central control point called a LAN Emulation Server (LES). A broadcast and
unknown server (BUS) acts as a central point to distribute broadcasts and multicasts. The LAN Emulation Configuration Server
(LECS) holds a database of LECs and the ELANs they belong to. The database is maintained by a network administrator.
These protocols are described in detail in the
Cisco Internetwork Design Guide .
ATM LANE Fast Simple Server Replication Protocol
To improve the ATM LANE Simple Server Replication Protocol (SSRP), Cisco introduced the ATM LANE Fast Simple Server Replication
Protocol (FSSRP). FSSRP differs from LANE SSRP in that all configured LANE servers of an ELAN are always active. FSSRP-enabled
LANE clients have virtual circuits (VCs) established to a maximum of four LANE servers and BUSs at one time. If a single LANE
server goes down, the LANE client quickly switches over to the next LANE server and BUS, resulting in no data or LE ARP table
entry loss and no extraneous signalling.
The FSSRP feature improves upon SSRP such that LANE server and BUS switchover for LANE clients is immediate. With SSRP, a
LANE server would go down, and depending on the network load, it may have taken considerable time for the LANE client to come
back up joined to the correct LANE server and BUS. In addition to going down with SSRP, the LANE client would do the following:
Clear out its data direct VCs
Clear out its LE ARP entries
Cause substantial signalling activity and data loss
FSSRP was designed to alleviate these problems with the LANE client. With FSSRP, each LANE client is simultaneously joined
to up to four LANE servers and BUSs. The concept of the master LANE server and BUS is maintained; the LANE client uses the
master LANE server when it needs LANE server BUS services. However, the difference between SSRP and FSSRP is that if and when
the master LANE server goes down, the LANE client is already connected to multiple backup LANE servers and BUSs. The LANE
client simply uses the next backup LANE server and BUS as the master LANE server and BUS.
VLAN Interoperability
Cisco IOS features bring added benefits to the VLAN technology. Enhancements to ISL, IEEE 802.10, and ATM LANE implementations
enable routing of all major protocols between VLANs. These enhancements allow users to create more robust networks incorporating
VLAN configurations by providing communications capabilities between VLANs.
Inter-VLAN Communications
The Cisco IOS supports full routing of several protocols over ISL and
ATM LANE VLANs. IP, Novell IPX, and AppleTalk routing are supported over IEEE
802.10 VLANs. Standard routing attributes such as network advertisements,
secondaries, and help addresses are applicable, and VLAN routing is fast
switched. The table below shows protocols supported for each VLAN encapsulation
format and corresponding Cisco IOS software releases in which support was
introduced.
Table 1. Inter-VLAN Routing Protocol Support
Protocol
ISL
ATM LANE
IEEE 802.10
IP
Release 11.1
Release 10.3
Release 11.1
Novell IPX (default encapsulation)
Release 11.1
Release 10.3
Release 11.1
Novell IPX (configurable encapsulation)
Release 11.3
Release 10.3
Release 11.3
AppleTalk Phase II
Release 11.3
Release 10.3
--
DECnet
Release 11.3
Release 11.0
--
Banyan VINES
Release 11.3
Release 11.2
--
XNS
Release 11.3
Release 11.2
--
CLNS
Release 12.1
--
--
IS-IS
Release 12.1
--
--
VLAN Translation
VLAN translation refers to the ability of the Cisco IOS software to translate between different VLANs or between VLAN and
non-VLAN encapsulating interfaces at Layer 2. Translation is typically used for selective inter-VLAN switching of nonroutable
protocols and to extend a single VLAN topology across hybrid switching environments. It is also possible to bridge VLANs on
the main interface; the VLAN encapsulating header is preserved. Topology changes in one VLAN domain do not affect a different
VLAN.
Designing Switched VLANs
By the time you are ready to configure routing between VLANs, you will have already defined them through the switches in
your network. Issues related to network design and VLAN definition should be addressed during your network design. See the
Cisco Internetwork Design Guide and the appropriate switch documentation for information on these topics:
Sharing resources between VLANs
Load balancing
Redundant links
Addressing
Segmenting networks with VLANs--Segmenting the network into broadcast groups improves network security. Use router access
lists based on station addresses, application types, and protocol types.
Routers and their role in switched networks--In switched networks, routers perform broadcast management, route processing,
and distribution, and provide communication between VLANs. Routers provide VLAN access to shared resources and connect to
other parts of the network that are either logically segmented with the more traditional subnet approach or require access
to remote sites across wide-area links.
Frame Tagging in ISL
ISL is a Cisco protocol for interconnecting multiple switches and
maintaining VLAN information as traffic goes between switches. ISL provides
VLAN capabilities while maintaining full wire speed performance on Fast
Ethernet links in full- or half-duplex mode. ISL operates in a point-to-point
environment and will support up to 1000 VLANs. You can define virtually as many
logical networks as are necessary for your environment.
With ISL, an Ethernet frame is encapsulated with a header that
transports VLAN IDs between switches and routers. A 26-byte header that
contains a 10-bit VLAN ID is propounded to the Ethernet frame.
A VLAN ID is added to the frame only when the frame is prepended for a
nonlocal network. The figure below shows VLAN packets traversing the shared
backbone. Each VLAN packet carries the VLAN ID within the packet header.
Figure 6. VLAN Packets Traversing the Shared Backbone
You can configure routing between any number of VLANs in your network.
This section documents the configuration tasks for each protocol supported with
ISL encapsulation. The basic process is the same, regardless of the protocol
being routed. It involves the following tasks:
Enabling the protocol on
the router
Enabling the protocol on
the interface
Defining the encapsulation
format as ISL or TRISL
Customizing the protocol
according to the requirements for your environment
IEEE 802.1Q-in-Q VLAN Tag
Termination on Subinterfaces
IEEE 802.1Q-in-Q VLAN
Tag Termination simply adds another layer of IEEE 802.1Q tag (called “metro
tag” or “PE-VLAN”) to the 802.1Q tagged packets that enter the network. The
purpose is to expand the VLAN space by tagging the tagged packets, thus
producing a “double-tagged” frame. The expanded VLAN space allows the service
provider to provide certain services, such as Internet access on specific VLANs
for specific customers, and yet still allows the service provider to provide
other types of services for their other customers on other VLANs.
Generally the service
provider’s customers require a range of VLANs to handle multiple applications.
Service providers can allow their customers to use this feature to safely
assign their own VLAN IDs on subinterfaces because these subinterface VLAN IDs
are encapsulated within a service-provider designated VLAN ID for that
customer. Therefore there is no overlap of VLAN IDs among customers, nor does
traffic from different customers become mixed. The double-tagged frame is
“terminated” or assigned on a subinterface with an expanded
encapsulation dot1q command that specifies the two VLAN ID tags
(outer VLAN ID and inner VLAN ID) terminated on the subinterface. See the
figure below.
IEEE 802.1Q-in-Q VLAN
Tag Termination is generally supported on whichever Cisco IOS features or
protocols are supported on the subinterface; the exception is that Cisco 10000
series Internet router only supports PPPoE. For example if you can run PPPoE on
the subinterface, you can configure a double-tagged frame for PPPoE. The only
restriction is whether you assign ambiguous or unambiguous subinterfaces for
the inner VLAN ID. See the figure below.
Note
The Cisco 10000
series Internet router only supports Point-to-Point Protocol over Ethernet
(PPPoE) and IP packets that are double-tagged for Q-in-Q VLAN tag termination.
Specifically PPPoEoQ-in-Q and IPoQ-in-Q are supported.
The primary benefit
for the service provider is reduced number of VLANs supported for the same
number of customers. Other benefits of this feature include:
PPPoE
scalability. By expanding the available VLAN space from 4096 to approximately
16.8 million (4096 times 4096), the number of PPPoE sessions that can be
terminated on a given interface is multiplied.
When deploying
Gigabyte Ethernet DSL Access Multiplexer (DSLAM) in wholesale model, you can
assign the inner VLAN ID to represent the end-customer virtual circuit (VC) and
assign the outer VLAN ID to represent the service provider ID.
The Q-in-Q VLAN tag
termination feature is simpler than the IEEE 802.1Q tunneling feature deployed
for the Catalyst 6500 series switches or the Catalyst 3550 and Catalyst 3750
switches. Whereas switches require IEEE 802.1Q tunnels on interfaces to carry
double-tagged traffic, routers need only encapsulate Q-in-Q VLAN tags within
another level of 802.1Q tags in order for the packets to arrive at the correct
destination as shown in figure below.
Figure 7. Untagged, 802.1Q-Tagged, and
Double-Tagged Ethernet Frames
Cisco 10000 Series Internet
Router Application
For the emerging
broadband Ethernet-based DSLAM market, the Cisco 10000 series Internet router
supports Q-in-Q encapsulation. With the Ethernet-based DSLAM model shown in the
figure below, customers typically get their own VLAN and all these VLANs are
aggregated on a DSLAM.
VLAN aggregation on a
DSLAM will result in a lot of aggregate VLANs that at some point need to be
terminated on the broadband remote access servers (BRAS). Although the model
could connect the DSLAMs directly to the BRAS, a more common model uses the
existing Ethernet-switched network where each DSLAM VLAN ID is tagged with a
second tag (Q-in-Q) as it connects into the Ethernet-switched network.
The only model that
is supported is PPPoE over Q-in-Q (PPPoEoQinQ). This can either be a PPP
terminated session or as a L2TP LAC session.
The Cisco 10000
series Internet router already supports plain PPPoE and PPP over 802.1Q
encapsulation. Supporting PPP over Q-in-Q encapsulation is new. PPP over Q-in-Q
encapsulation processing is an extension to 802.1q encapsulation processing. A
Q-in-Q frame looks like a VLAN 802.1Q frame, only it has two 802.1Q tags
instead of one.
PPP over Q-in-Q
encapsulation supports configurable outer tag Ethertype. The configurable
Ethertype field values are 0x8100 (default), 0x9100, and 0x9200. See the figure
below.
Security ACL Application on the Cisco 10000 Series Internet Router
The IEEE 802.1Q-in-Q VLAN Tag Termination feature provides limited security access control list (ACL) support for the Cisco
10000 series Internet router.
If you apply an ACL to PPPoE traffic on a Q-in-Q subinterface in a VLAN, apply the ACL directly on the PPPoE session, using
virtual access interfaces (VAIs) or RADIUS attribute 11 or 242.
You can apply ACLs to virtual access interfaces by configuring them under virtual template interfaces. You can also configure
ACLs by using RADIUS attribute 11 or 242. When you use attribute 242, a maximum of 30,000 sessions can have ACLs.
ACLs that are applied to the VLAN Q-in-Q subinterface have no effect and are silently ignored. In the following example, ACL
1 that is applied to the VLAN Q-in-Q subinterface level will be ignored:
The
encapsulation dot1q command is used to configure Q-in-Q termination on a subinterface. The command accepts an Outer VLAN ID and one or more Inner
VLAN IDs. The outer VLAN ID always has a specific value, while inner VLAN ID can either be a specific value or a range of
values.
A subinterface that is configured with a single Inner VLAN ID is called an unambiguous Q-in-Q subinterface. In the following
example, Q-in-Q traffic with an Outer VLAN ID of 101 and an Inner VLAN ID of 1001 is mapped to the Gigabit Ethernet 1/0.100
subinterface:
A subinterface that is configured with multiple Inner VLAN IDs is called an ambiguous Q-in-Q subinterface. By allowing multiple
Inner VLAN IDs to be grouped together, ambiguous Q-in-Q subinterfaces allow for a smaller configuration, improved memory usage
and better scalability.
In the following example, Q-in-Q traffic with an Outer VLAN ID of 101 and Inner VLAN IDs anywhere in the 2001-2100 and 3001-3100
range is mapped to the Gigabit Ethernet 1/0.101 subinterface.:
Ambiguous subinterfaces can also use the
any keyword to specify the inner VLAN ID.
See the Monitoring and Maintaining VLAN Subinterfaces section for an example of how VLAN IDs are assigned to subinterfaces,
and for a detailed example of how the
any keyword is used on ambiguous subinterfaces.
Only PPPoE is supported on ambiguous subinterfaces. Standard IP routing is not supported on ambiguous subinterfaces.
Note
On the Cisco 10000 series Internet router, Modular QoS services are only supported on unambiguous subinterfaces.
How to Configure Routing Between VLANS
Configuring a VLAN Range
Using the VLAN Range feature, you can group VLAN subinterfaces together so that any command entered in a group applies to
every subinterface within the group. This capability simplifies configurations and reduces command parsing.
The VLAN Range feature provides the following benefits:
Simultaneous Configurations: Identical commands can be entered once for a range of subinterfaces, rather than being entered
separately for each subinterface.
Overlapping Range Configurations: Overlapping ranges of subinterfaces can be configured.
Customized Subinterfaces: Individual subinterfaces within a range can be customized or deleted.
Restrictions
Each command you enter while you are in interface configuration mode with the interface range command is executed as it is entered. The commands are not batched together for execution after you exit interface configuration
mode. If you exit interface configuration mode while the commands are being executed, some commands might not be executed
on some interfaces in the range. Wait until the command prompt reappears before exiting interface configuration mode.
The no interface range command is not supported. You must delete individual subinterfaces to delete a range.
Configuring a Range of VLAN Subinterfaces
Use the following commands to configure a range of VLAN subinterfaces.
Router(config)# interface range fastethernet5/1.1 - fastethernet5/1.4
Selects the range of subinterfaces to be configured.
Note
The spaces around the dash are required. For example, the command interface range fastethernet 1 - 5 is valid; the command interface range fastethernet 1-5 is not valid.
Step 4
encapsulation dot1Q vlan-id
Example:
Router(config-if)# encapsulation dot1Q 301
Applies a unique VLAN ID to each subinterface within the range.
vlan-id--Virtual LAN identifier. The allowed range is from 1 to 4095.
The VLAN ID specified by the vlan-id argument is applied to the first subinterface in the range. Each subsequent interface is assigned a VLAN ID, which is the
specified vlan-id plus the subinterface number minus the first subinterface number (VLAN ID + subinterface number - first subinterface number).
Step 5
no shutdown
Example:
Router(config-if)# no shutdown
Activates the interface.
This command is required only if you shut down the interface.
Step 6
exit
Example:
Router(config-if)# exit
Returns to privileged EXEC mode.
Step 7
show running-config
Example:
Router# show running-config
Verifies subinterface configuration.
Step 8
show interfaces
Example:
Router# show interfaces
Verifies that subinterfaces have been created.
Configuring Routing Between VLANs with Inter-Switch Link Encapsulation
This section describes the Inter-Switch Link (ISL) protocol and provides guidelines for configuring ISL and Token Ring ISL
(TRISL) features. This section contains the following:
Configuring AppleTalk Routing over ISL
AppleTalk can be routed over VLAN subinterfaces using the ISL and IEEE 802.10 VLAN encapsulation protocols. The AppleTalk
Routing over ISL and IEEE 802.10 Virtual LANs feature provides full-feature Cisco IOS software AppleTalk support on a per-VLAN
basis, allowing standard AppleTalk capabilities to be configured on VLANs.
To route AppleTalk over ISL or IEEE 802.10 between VLANs, you need to customize the subinterface to create the environment
in which it will be used. Perform the steps in the order in which they appear.
SUMMARY STEPS
enable
configure terminal
appletalk routing [eigrp router-number]
interface typeslot/ port. subinterface-number
encapsulation isl vlan-identifier
appletalk cable-range cable-range [network. node]
appletalk zone zone-name
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
appletalk routing [eigrp router-number]
Example:
Router(config)# appletalk routing
Enables AppleTalk routing globally on either ISL or 802.10 interfaces.
Step 4
interface typeslot/ port. subinterface-number
Example:
Router(config)# interface Fddi 1/0.100
Specifies the subinterface the VLAN will use.
Step 5
encapsulation isl vlan-identifier
Example:
Example:
or
Example:
encapsulation sde said
Example:
Router(config-if)# encapsulation sde 100
Defines the encapsulation format as either ISL (isl ) or IEEE 802.10 (sde ), and specifies the VLAN identifier or security association identifier, respectively.
Assigns the AppleTalk cable range and zone for the subinterface.
Step 7
appletalk zone zone-name
Example:
Router(config-if)# appletalk zone 100
Assigns the AppleTalk zone for the subinterface.
Configuring Banyan VINES Routing over ISL
Banyan VINES can be routed over VLAN subinterfaces using the ISL encapsulation protocol. The Banyan VINES Routing over ISL
Virtual LANs feature provides full-feature Cisco IOS software Banyan VINES support on a per-VLAN basis, allowing standard
Banyan VINES capabilities to be configured on VLANs.
To route Banyan VINES over ISL between VLANs, you need to configure ISL encapsulation on the subinterface. Perform the steps
in the following task in the order in which they appear:
SUMMARY STEPS
enable
configure terminal
vines routing [address]
interface typeslot/ port. subinterface-number
encapsulation isl vlan-identifier
vines metric [whole [fraction]]
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
vines routing [address]
Example:
Router(config)# vines routing
Enables Banyan VINES routing globally.
Step 4
interface typeslot/ port. subinterface-number
Example:
Router(config)# interface fastethernet 1/0.1
Specifies the subinterface on which ISL will be used.
Step 5
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 200
Defines the encapsulation format as ISL (isl ), and specifies the VLAN identifier.
Step 6
vines metric [whole [fraction]]
Example:
Router(config-if)#vines metric 2
Enables VINES routing metric on an interface.
Configuring DECnet Routing over ISL
DECnet can be routed over VLAN subinterfaces using the ISL VLAN encapsulation protocols. The DECnet Routing over ISL Virtual
LANs feature provides full-feature Cisco IOS software DECnet support on a per-VLAN basis, allowing standard DECnet capabilities
to be configured on VLANs.
To route DECnet over ISL VLANs, you need to configure ISL encapsulation on the subinterface. Perform the steps described in
the following task in the order in which they appear.
Specifies the subinterface on which ISL will be used.
Step 5
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 200
Defines the encapsulation format as ISL (isl ), and specifies the VLAN identifier.
Step 6
decnet cost [cost-value]
Example:
Router(config-if)# decnet cost 4
Enables DECnet cost metric on an interface.
Configuring the Hot Standby Router Protocol over ISL
The Hot Standby Router Protocol (HSRP) provides fault tolerance and enhanced routing performance for IP networks. HSRP allows
Cisco IOS routers to monitor each other’s operational status and very quickly assume packet forwarding responsibility in the
event the current forwarding device in the HSRP group fails or is taken down for maintenance. The standby mechanism remains
transparent to the attached hosts and can be deployed on any LAN type. With multiple Hot Standby groups, routers can simultaneously
provide redundant backup and perform loadsharing across different IP subnets.
The figure below illustrates HSRP in use with ISL providing routing between several VLANs.
Figure 8. Hot Standby Router Protocol in VLAN Configurations
A separate HSRP group is configured for each VLAN subnet so that Cisco IOS router A can be the primary and forwarding router
for VLANs 10 and 20. At the same time, it acts as backup for VLANs 30 and 40. Conversely, Router B acts as the primary and
forwarding router for ISL VLANs 30 and 40, as well as the secondary and backup router for distributed VLAN subnets 10 and
20.
Running HSRP over ISL allows users to configure redundancy between multiple routers that are configured as front ends for
VLAN IP subnets. By configuring HSRP over ISLs, users can eliminate situations in which a single point of failure causes traffic
interruptions. This feature inherently provides some improvement in overall networking resilience by providing load balancing
and redundancy capabilities between subnets and VLANs.
To configure HSRP over ISLs between VLANs, you need to create the environment in which it will be used. Perform the tasks
described in the following sections in the order in which they appear.
Configures the time between hello packets and the hold time before other routers declare the active router to be down.
Step 8
standby [group-number]
priority priority
Example:
Router(config-if)# standby 1 priority 105
Sets the Hot Standby priority used to choose the active router.
Step 9
standby [group-number]
preempt
Example:
Router(config-if)# standby 1 priority 105
Specifies that if the local router has priority over the current active router, the local router should attempt to take its
place as the active router.
Configures the interface to track other interfaces, so that if one of the other interfaces goes down, the Hot Standby priority
for the device is lowered.
The DRiP database is automatically enabled when TRISL encapsulation is configured, and at least one TrBRF is defined, and
the interface is configured for SRB or for routing with RIF.
Step 6
ip address ip-address mask
Example:
Router(config-if# ip address 10.5.5.1 255.255.255.0
Sets a primary IP address for an interface.
A mask identifies the bits that denote the network number in an IP address. When you use the mask to subnet a network, the
mask is then referred to as a subnetmask.
Note
TRISL encapsulation must be specified for a subinterface before an IP address can be assigned to that subinterface.
Configuring IPX Routing on 802.10 VLANs over ISL
The IPX Encapsulation for 802.10 VLAN feature provides configurable IPX (Novell-FDDI, SAP, SNAP) encapsulation over 802.10
VLAN on router FDDI interfaces to connect the Catalyst 5000 VLAN switch. This feature extends Novell NetWare routing capabilities
to include support for routing all standard IPX encapsulations for Ethernet frame types in VLAN configurations. Users with
Novell NetWare environments can now configure any one of the three IPX Ethernet encapsulations to be routed using Secure Data
Exchange (SDE) encapsulation across VLAN boundaries. IPX encapsulation options now supported for VLAN traffic include the
following:
Novell-FDDI (IPX FDDI RAW to 802.10 on FDDI)
SAP (IEEE 802.2 SAP to 802.10 on FDDI)
SNAP (IEEE 802.2 SNAP to 802.10 on FDDI)
NetWare users can now configure consolidated VLAN routing over a single VLAN trunking FDDI interface. Not all IPX encapsulations
are currently supported for SDE VLAN. The IPX interior encapsulation support can be achieved by messaging the IPX header before
encapsulating in the SDE format. Fast switching will also support all IPX interior encapsulations on non-MCI platforms (for
example non-AGS+ and non-7000). With configurable Ethernet encapsulation protocols, users have the flexibility of using VLANs
regardless of their NetWare Ethernet encapsulation. Configuring Novell IPX encapsulations on a per-VLAN basis facilitates
migration between versions of Netware. NetWare traffic can now be routed across VLAN boundaries with standard encapsulation
options (arpa ,
sap , and
snap ) previously unavailable. Encapsulation types and corresponding framing types are described in the “Configuring Novell IPX
” module of the
Cisco IOS Novell IPX Configuration Guide .
Note
Only one type of IPX encapsulation can be configured per VLAN (subinterface). The IPX encapsulation used must be the same
within any particular subnet; a single encapsulation must be used by all NetWare systems that belong to the same VLAN.
To configure Cisco IOS software on a router with connected VLANs to exchange different IPX framing protocols, perform the
steps described in the following task in the order in which they are appear.
Router(config-if)# ipx network 20 encapsulation sap
Specifies the IPX encapsulation among Novell-FDDI, SAP, or SNAP.
Configuring IPX Routing over TRISL
The IPX Routing over ISL VLANs feature extends Novell NetWare routing capabilities to include support for routing all standard
IPX encapsulations for Ethernet frame types in VLAN configurations. Users with Novell NetWare environments can configure either
SAP or SNAP encapsulations to be routed using the TRISL encapsulation across VLAN boundaries. The SAP (Novell Ethernet_802.2)
IPX encapsulation is supported for VLAN traffic.
NetWare users can now configure consolidated VLAN routing over a single VLAN trunking interface. With configurable Ethernet
encapsulation protocols, users have the flexibility of using VLANs regardless of their NetWare Ethernet encapsulation. Configuring
Novell IPX encapsulations on a per-VLAN basis facilitates migration between versions of Netware. NetWare traffic can now be
routed across VLAN boundaries with standard encapsulation options (sap and
snap ) previously unavailable. Encapsulation types and corresponding framing types are described in the “Configuring Novell IPX
” module of the
Cisco IOS Novell IPX Configuration Guide .
Note
Only one type of IPX encapsulation can be configured per VLAN (subinterface). The IPX encapsulation used must be the same
within any particular subnet: A single encapsulation must be used by all NetWare systems that belong to the same LANs.
To configure Cisco IOS software to exchange different IPX framing protocols on a router with connected VLANs, perform the
steps in the following task in the order in which they are appear.
Router(config-if)# ipx network 100 encapsulation sap
Specifies the IPX encapsulation on the subinterface by specifying the NetWare network number (if necessary) and the encapsulation
type.
What to do next
Note
The default IPX encapsulation format for Cisco IOS routers is “novell-ether” (Novell Ethernet_802.3). If you are running
Novell Netware 3.12 or 4.0, the new Novell default encapsulation format is Novell Ethernet_802.2 and you should configure
the Cisco router with the IPX encapsulation format “sap.”
Configuring VIP Distributed Switching over ISL
With the introduction of the VIP distributed ISL feature, ISL
encapsulated IP packets can be switched on Versatile Interface Processor (VIP)
controllers installed on Cisco 7500 series routers.
The second generation VIP2 provides distributed switching of IP
encapsulated in ISL in VLAN configurations. Where an aggregation route performs
inter-VLAN routing for multiple VLANs, traffic can be switched autonomously
on-card or between cards rather than through the central Route Switch Processor
(RSP). The figure below shows the VIP distributed architecture of the Cisco
7500 series router.
Figure 9. Cisco 7500 Distributed Architecture
This distributed architecture allows incremental capacity increases
by installation of additional VIP cards. Using VIP cards for switching the
majority of IP VLAN traffic in multiprotocol environments substantially
increases routing performance for the other protocols because the RSP offloads
IP and can then be dedicated to switching the non-IP protocols.
VIP distributed switching offloads switching of ISL VLAN IP traffic
to the VIP card, removing involvement from the main CPU. Offloading ISL traffic
to the VIP card substantially improves networking performance. Because you can
install multiple VIP cards in a router, VLAN routing capacity is increased
linearly according to the number of VIP cards installed in the router.
To configure distributed switching on the VIP, you must first
configure the router for IP routing. Perform the tasks described below in the
order in which they appear.
SUMMARY STEPS
enable
configure terminal
ip routing
interface typeslot/ port-adapter/ port
ip route-cache distributed
encapsulation isl vlan-identifier
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password
if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
ip routing
Example:
Router(config)# ip routing
Enables IP routing on the router.
For more information
about configuring IP routing, see the appropriate Cisco IOS
IP Routing Configuration Guide for the version of Cisco
IOS you are using.
Step 4
interface typeslot/ port-adapter/ port
Example:
Router(config)# interface FastEthernet1/0/0
Specifies the interface and enters interface configuration mode.
Step 5
ip route-cache distributed
Example:
Router(config-if)# ip route-cache distributed
Enables VIP distributed switching of IP packets on the interface.
Step 6
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 1
Defines the encapsulation format as ISL, and specifies the VLAN
identifier.
Configuring XNS Routing over ISL
XNS can be routed over VLAN subinterfaces using the ISL VLAN encapsulation protocol. The XNS Routing over ISL Virtual LANs
feature provides full-feature Cisco IOS software XNS support on a per-VLAN basis, allowing standard XNS capabilities to be
configured on VLANs.
To route XNS over ISL VLANs, you need to configure ISL encapsulation on the subinterface. Perform the steps described in the
following task in the order in which they appear.
SUMMARY STEPS
enable
configure terminal
xns routing [address]
interface typeslot/ port. subinterface-number
encapsulation isl vlan-identifier
xns network [number]
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
xns routing [address]
Example:
Router(config)# xns routing 0123.4567.adcb
Enables XNS routing globally.
Step 4
interface typeslot/ port. subinterface-number
Example:
Router(config)# interface fastethernet 1/0.1
Specifies the subinterface on which ISL will be used and enters interface configuration mode.
Step 5
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 100
Defines the encapsulation format as ISL (isl ), and specifies the VLAN identifier.
Step 6
xns network [number]
Example:
Router(config-if)# xns network 20
Enables XNS routing on the subinterface.
Configuring CLNS Routing over ISL
CLNS can be routed over VLAN subinterfaces using the ISL VLAN encapsulation protocol. The CLNS Routing over ISL Virtual LANs
feature provides full-feature Cisco IOS software CLNS support on a per-VLAN basis, allowing standard CLNS capabilities to
be configured on VLANs.
To route CLNS over ISL VLANs, you need to configure ISL encapsulation on the subinterface. Perform the steps described in
the following task in the order in which they appear.
SUMMARY STEPS
enable
configure terminal
clns routing
interface typeslot/ port. subinterface-number
encapsulation isl vlan-identifier
clns enable
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
clns routing
Example:
Router(config)# clns routing
Enables CLNS routing globally.
Step 4
interface typeslot/ port. subinterface-number
Example:
Router(config-if)# interface fastethernet 1/0.1
Specifies the subinterface on which ISL will be used and enters interface configuration mode.
Step 5
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 100
Defines the encapsulation format as ISL (isl ), and specifies the VLAN identifier.
Step 6
clns enable
Example:
Router(config-if)# clns enable
Enables CLNS routing on the subinterface.
Configuring IS-IS Routing over ISL
IS-IS routing can be enabled over VLAN subinterfaces using the ISL VLAN encapsulation protocol. The IS-IS Routing over ISL
Virtual LANs feature provides full-feature Cisco IOS software IS-IS support on a per-VLAN basis, allowing standard IS-IS capabilities
to be configured on VLANs.
To enable IS-IS over ISL VLANs, you need to configure ISL encapsulation on the subinterface. Perform the steps described in
the following task in the order in which they appear.
SUMMARY STEPS
enable
configure terminal
router isis [tag]
net network-entity-title
interface typeslot/ port. subinterface-number
encapsulation isl vlan-identifier
clns router isis network [tag]
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
router isis [tag]
Example:
Router(config)# isis routing test-proc2
Enables IS-IS routing, and enters router configuration mode.
Step 4
net network-entity-title
Example:
Router(config)# net 49.0001.0002.aaaa.aaaa.aaaa.00
Configures the NET for the routing process.
Step 5
interface typeslot/ port. subinterface-number
Example:
Router(config)# interface fastethernet 2.
Specifies the subinterface on which ISL will be used and enters interface configuration mode.
Step 6
encapsulation isl vlan-identifier
Example:
Router(config-if)# encapsulation isl 101
Defines the encapsulation format as ISL (isl ), and specifies the VLAN identifier.
Specifies the interfaces that should be actively routing IS-IS.
Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation
This section describes the required and optional tasks for configuring routing between VLANs with IEEE 802.1Q encapsulation.
The IEEE 802.1Q protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies.
Prerequisites
Configuring routing between VLANs with IEEE 802.1Q encapsulation assumes the presence of a single spanning tree and of an
explicit tagging scheme with one-level tagging.
You can configure routing between any number of VLANs in your network.
Restrictions
The IEEE 802.1Q standard is extremely restrictive to untagged frames. The standard provides only a per-port VLANs solution
for untagged frames. For example, assigning untagged frames to VLANs takes into consideration only the port from which they
have been received. Each port has a parameter called a permanent virtual identification
(Native VLAN) that specifies the VLAN assigned to receive untagged frames.
The main characteristics of the IEEE 802.1Q are that it assigns frames to VLANs by filtering and that the standard assumes
the presence of a single spanning tree and of an explicit tagging scheme with one-level tagging.
This section contains the configuration tasks for each protocol supported with IEEE 802.1Q encapsulation. The basic process
is the same, regardless of the protocol being routed. It involves the following tasks:
Enabling the protocol on the router
Enabling the protocol on the interface
Defining the encapsulation format as IEEE 802.1Q
Customizing the protocol according to the requirements for your environment
To configure IEEE 802.1Q on your network, perform the following tasks. One of the following tasks is required depending on
the protocol being used.
The following tasks are optional. Perform the following tasks to connect a network of hosts over a simple bridging-access
device to a remote access concentrator bridge between IEEE 802.1Q VLANs. The following sections contain configuration tasks
for the Integrated Routing and Bridging, Transparent Bridging, and PVST+ Between VLANs with IEEE 802.1Q Encapsulation:
AppleTalk can be routed over virtual LAN (VLAN) subinterfaces using the IEEE 802.1Q VLAN encapsulation protocol. AppleTalk
Routing provides full-feature Cisco IOS software AppleTalk support on a per-VLAN basis, allowing standard AppleTalk capabilities
to be configured on VLANs.
To route AppleTalk over IEEE 802.1Q between VLANs, you need to customize the subinterface to create the environment in which
it will be used. Perform the steps in the order in which they appear.
Use the following task to enable AppleTalk routing on IEEE 802.1Q interfaces.
Assigns the AppleTalk cable range and zone for the subinterface.
Step 7
appletalk zone zone-name
Example:
Router(config-if)# appletalk zone eng
Assigns the AppleTalk zone for the subinterface.
What to do next
Note
For more information on configuring AppleTalk, see the “Configuring AppleTalk” module in the
Cisco IOS AppleTalk Configuration Guide .
Configuring IP Routing over IEEE 802.1Q
IP routing over IEEE 802.1Q extends IP routing capabilities to include support for routing IP frame types in VLAN configurations
using the IEEE 802.1Q encapsulation.
To route IP over IEEE 802.1Q between VLANs, you need to customize the subinterface to create the environment in which it will
be used. Perform the tasks described in the following sections in the order in which they appear.
Specifies the subinterface on which IEEE 802.1Q will be used and enters interface configuration mode.
Step 5
encapsulation dot1q vlanid
Example:
Router(config-if)# encapsulation dot1q 101
Defines the encapsulation format at IEEE.802.1Q (dot1q) and specifies the VLAN identifier.
Step 6
ip address ip-addressmask
Example:
Router(config-if)# ip addr 10.0.0.11 255.0.0.0
Sets a primary IP address and mask for the interface.
What to do next
Once you have IP routing enabled on the router, you can customize the characteristics to suit your environment. See the appropriate
Cisco IOS IP Routing Configuration Guide
for the version of Cisco IOS you are using.
Configuring IPX Routing over IEEE 802.1Q
IPX routing over IEEE 802.1Q VLANs extends Novell NetWare routing capabilities to include support for routing Novell Ethernet_802.3
encapsulation frame types in VLAN configurations. Users with Novell NetWare environments can configure Novell Ethernet_802.3
encapsulation frames to be routed using IEEE 802.1Q encapsulation across VLAN boundaries.
To configure Cisco IOS software on a router with connected VLANs to exchange IPX Novell Ethernet_802.3 encapsulated frames,
perform the steps described in the following task in the order in which they appear.
Defines the encapsulation format at IEEE.802.1Q (dot1q ) and specifies the VLAN identifier. VLAN 20 is specified as the native VLAN.
Note
If there is no explicitly defined native VLAN, the default VLAN1 becomes the native VLAN.
Step 5
bridge-group bridge-group
Example:
Router(config-subif)# bridge-group 1
Assigns the bridge group to the interface.
What to do next
Note
If there is an explicitly defined native VLAN, VLAN1 will only be used to process CST.
Configuring IEEE 802.1Q-in-Q VLAN Tag Termination
Encapsulating IEEE 802.1Q VLAN tags within 802.1Q enables service providers to use a single VLAN to support customers who
have multiple VLANs. The IEEE 802.1Q-in-Q VLAN Tag Termination feature on the subinterface level preserves VLAN IDs and keeps
traffic in different customer VLANs segregated.
You must have checked Feature Navigator to verify that your Cisco device and software image support this feature.
You must be connected to an Ethernet device that supports double VLAN tag imposition/disposition or switching.
The following restrictions apply to the Cisco 10000 series Internet router for configuring IEEE 802.1Q-in-Q VLAN tag termination:
Supported on Ethernet, FastEthernet, or Gigabit Ethernet interfaces.
Supports only Point-to-Point Protocol over Ethernet (PPPoE) packets that are double-tagged for Q-in-Q VLAN tag termination.
IP and Multiprotocol Label Switching (MPLS) packets are not supported.
Modular QoS can be applied to unambiguous subinterfaces only.
Limited ACL support.
Perform these tasks to configure the main interface used for the Q-in-Q double tagging and to configure the subinterfaces.
Configuring EtherType Field for Outer VLAN Tag Termination
The following restrictions are applicable for the Cisco 10000 series Internet router:
PPPoE is already configured.
Virtual private dial-up network (VPDN) is enabled.
The first task is optional. A step in this task shows you how to configure the EtherType field to be 0x9100 for the outer
VLAN tag, if that is required.
After the subinterface is defined, the 802.1Q encapsulation is configured to use the double tagging.
To configure the EtherType field for Outer VLAN Tag Termination, use the following steps. This task is optional.
SUMMARY STEPS
enable
configure terminal
interface typenumber
dot1q tunneling ethertype ethertype
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
interface typenumber
Example:
Router(config)# interface gigabitethernet 1/0/0
Configures an interface and enters interface configuration mode.
Step 4 enables the 802.1Q encapsulation of traffic on a specified subinterface in a VLAN.
Use the
second-dot1q keyword and the
vlan-idargument to specify the VLAN tags to be terminated on the subinterface.
In the example, an ambiguous Q-in-Q subinterface is configured because a range of inner VLAN IDs is specified.
Q-in-Q frames with an outer VLAN ID of 100 and an inner VLAN ID in the range of 100 to 199 or 201 to 600 will be terminated.
Step 5 enables PPPoE sessions on the subinterface. The example specifies that the PPPoE profile, vpn1, will be used by PPPoE
sessions on the subinterface.
Note
Step 5 is required for the Cisco 10000 series Internet router because it only supports PPPoEoQinQ traffic.
Step 9
end
Example:
Router(config-subif)# end
Exits subinterface configuration mode and returns to privileged EXEC mode.
Verifying the IEEE 802.1Q-in-Q VLAN Tag Termination
Perform this optional task to verify the configuration of the IEEE 802.1Q-in-Q VLAN Tag Termination feature.
Enables privileged EXEC mode. Enter your password if prompted.
Example:
Router> enable
Step 2
show running-config
Use this command to show the currently running configuration on the device. You can use delimiting characters to display only
the relevant parts of the configuration.
The following shows the currently running configuration on a Cisco 7300 series router:
Use this command to show the statistics for all the 802.1Q VLAN IDs. In this example, only the outer VLAN ID is displayed.
Note
The show vlans dot1q command is not supported on the Cisco 10000 series Internet router.
Example:
Router# show vlans dot1q
Total statistics for 802.1Q VLAN 1:
441 packets, 85825 bytes input
1028 packets, 69082 bytes output
Total statistics for 802.1Q VLAN 101:
5173 packets, 510384 bytes input
3042 packets, 369567 bytes output
Total statistics for 802.1Q VLAN 201:
1012 packets, 119254 bytes input
1018 packets, 120393 bytes output
Total statistics for 802.1Q VLAN 301:
3163 packets, 265272 bytes input
1011 packets, 120750 bytes output
Total statistics for 802.1Q VLAN 401:
1012 packets, 119254 bytes input
1010 packets, 119108 bytes output
Monitoring and Maintaining VLAN Subinterfaces
Use the following task to determine whether a VLAN is a native VLAN.
SUMMARY STEPS
enable
show vlans
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
show vlans
Example:
Router# show vlans
Displays VLAN subinterfaces.
Monitoring and Maintaining VLAN Subinterfaces Example
The following is sample output from the show vlans command indicating a native VLAN and a bridged group:
Router# show vlans
Virtual LAN ID: 1 (IEEE 802.1Q Encapsulation)
vLAN Trunk Interface: FastEthernet1/0/2
This is configured as native Vlan for the following interface(s) :
FastEthernet1/0/2
Protocols Configured: Address: Received: Transmitted:
Virtual LAN ID: 100 (IEEE 802.1Q Encapsulation)
vLAN Trunk Interface: FastEthernet1/0/2.1
Protocols Configured: Address: Received: Transmitted:
Bridging Bridge Group 1 0 0
The following is sample output from the show vlans command that shows the traffic count on Fast Ethernet subinterfaces:
Router# show vlans
Virtual LAN ID: 2 (IEEE 802.1Q Encapsulation)
vLAN Trunk Interface: FastEthernet5/0.1
Protocols Configured: Address: Received: Transmitted:
IP 172.16.0.3 16 92129
Virtual LAN ID: 3 (IEEE 802.1Q Encapsulation)
vLAN Trunk Interface: Ethernet6/0/1.1
Protocols Configured: Address: Received: Transmitted:
IP 172.20.0.3 1558 1521
Virtual LAN ID: 4 (Inter Switch Link Encapsulation)
vLAN Trunk Interface: FastEthernet5/0.2
Protocols Configured: Address: Received: Transmitted:
IP 172.30.0.3 0 7
Configuration Examples for Configuring Routing Between VLANs
Single Range Configuration Example
The following example configures the Fast Ethernet subinterfaces within the range 5/1.1 and 5/1.4 and applies the following
VLAN IDs to those subinterfaces:
Fast Ethernet5/1.1 = VLAN ID 301 (vlan-id)
Fast Ethernet5/1.2 = VLAN ID 302 (vlan-id = 301 + 2 - 1 = 302)
Fast Ethernet5/1.3 = VLAN ID 303 (vlan-id = 301 + 3 - 1 = 303)
Fast Ethernet5/1.4 = VLAN ID 304 (vlan-id = 301 + 4 - 1 = 304)
Router(config)# interface range fastethernet5/1.1 - fastethernet5/1.4
Router(config-if)# encapsulation dot1Q 301
Router(config-if)# no shutdown
Router(config-if)#
*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.1, changed state to up
*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.2, changed state to up
*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.3, changed state to up
*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1.4, changed state to up
*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.1, changed state to up
*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.2, changed state to up
*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.3, changed state to up
*Oct 6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/1.4, changed state to up
ISL Encapsulation Configuration Examples
This section provides the following configuration examples for each of the protocols described in this module:
AppleTalk Routing over ISL Configuration Example
The configuration example illustrated in the figure below shows
AppleTalk being routed between different ISL and IEEE 802.10 VLAN encapsulating
subinterfaces.
Figure 10. Routing AppleTalk over VLAN Encapsulations
As shown in the figure above, AppleTalk traffic is routed to and from
switched VLAN domains 3, 4, 100, and 200 to any other AppleTalk routing
interface. This example shows a sample configuration file for the Cisco 7500
series router with the commands entered to configure the network shown in the
figure above.
Banyan VINES Routing over ISL Configuration Example
To configure routing of the Banyan VINES protocol over ISL trunks, you need to define ISL as the encapsulation type. This
example shows Banyan VINES configured to be routed over an ISL trunk:
To configure routing the DECnet protocol over ISL trunks, you need to define ISL as the encapsulation type. This example shows
DECnet configured to be routed over an ISL trunk:
The configuration example shown in the figure below shows HSRP being
used on two VLAN routers sending traffic to and from ISL VLANs through a
Catalyst 5000 switch. Each router forwards its own traffic and acts as a
standby for the other.
Figure 11. Hot Standby Router Protocol Sample Configuration
The topology shown in the figure above shows a Catalyst VLAN switch
supporting Fast Ethernet connections to two routers running HSRP. Both routers
are configured to route HSRP over ISLs.
The standby conditions are determined by the standby commands used in
the configuration. Traffic from Host 1 is forwarded through Router A. Because
the priority for the group is higher, Router A is the active router for Host 1.
Because the priority for the group serviced by Host 2 is higher in Router B,
traffic from Host 2 is forwarded through Router B, making Router B its active
router.
In the configuration shown in the figure above, if the active router
becomes unavailable, the standby router assumes active status for the
additional traffic and automatically routes the traffic normally handled by the
router that has become unavailable.
Host 1 Configuration
interface Ethernet 1/2
ip address 10.1.1.25 255.255.255.0
ip route 0.0.0.0 0.0.0.0 10.1.1.101
Host 2 Configuration
interface Ethernet 1/2
ip address 10.1.1.27 255.255.255.0
ip route 0.0.0.0 0.0.0.0 10.1.1.102
!
Router A Configuration
interface FastEthernet 1/1.110
encapsulation isl 110
ip address 10.1.1.2 255.255.255.0
standby 1 ip 10.1.1.101
standby 1 preempt
standby 1 priority 105
standby 2 ip 10.1.1.102
standby 2 preempt
!
end
!
set vlan 110 5/4
set vlan 110 5/3
set trunk 2/8 110
set trunk 2/9 110
IP Routing with RIF Between TrBRF VLANs Example
The figure below shows IP routing with RIF between two TrBRF VLANs.
Figure 12. IP Routing with RIF Between TrBRF VLANs
The following is the configuration for the router:
interface FastEthernet4/0.1
ip address 10.5.5.1 255.255.255.0
encapsulation tr-isl trbrf-vlan 999 bridge-num 14
multiring trcrf-vlan 200 ring 100
multiring all
!
interface FastEthernet4/0.2
ip address 10.4.4.1 255.255.255.0
encapsulation tr-isl trbrf-vlan 998 bridge-num 13
multiring trcrf-vlan 300 ring 101
multiring all
The following is the configuration for the Catalyst 5000 switch with
the Token Ring switch module in slot 5. In this configuration, the Token Ring
port 102 is assigned with TrCRF VLAN 40 and the Token Ring port 103 is assigned
with TrCRF VLAN 50:
#vtp
set vtp domain trisl
set vtp mode server
set vtp v2 enable
#drip
set set tokenring reduction enable
set tokenring distrib-crf disable
#vlans
set vlan 999 name trbrf type trbrf bridge 0xe stp ieee
set vlan 200 name trcrf200 type trcrf parent 999 ring 0x64 mode srb
set vlan 40 name trcrf40 type trcrf parent 999 ring 0x66 mode srb
set vlan 998 name trbrf type trbrf bridge 0xd stp ieee
set vlan 300 name trcrf300 type trcrf parent 998 ring 0x65 mode srb
set vlan 50 name trcrf50 type trcrf parent 998 ring 0x67 mode srb
#add token port to trcrf 40
set vlan 40 5/1
#add token port to trcrf 50
set vlan 50 5/2
set trunk 1/2 on
IP Routing Between a TRISL VLAN and an Ethernet ISL VLAN Example
The figure below shows IP routing between a TRISL VLAN and an
Ethernet ISL VLAN.
Figure 13. IP Routing Between a TRISL VLAN and an Ethernet ISL
VLAN
The following is the configuration for the router:
interface FastEthernet4/0.1
ip address 10.5.5.1 255.255.255.0
encapsulation tr-isl trbrf-vlan 999 bridge-num 14
multiring trcrf-vlan 20 ring 100
multiring all
!
interface FastEthernet4/0.2
ip address 10.4.4.1 255.255.255.0
encapsulation isl 12
IPX Routing over ISL Configuration Example
The figure below shows IPX interior encapsulations configured over
ISL encapsulation in VLAN configurations. Note that three different IPX
encapsulation formats are used. VLAN 20 uses SAP encapsulation, VLAN 30 uses
ARPA, and VLAN 70 uses novell-ether encapsulation. Prior to the introduction of
this feature, only the default encapsulation format, “novell-ether,” was
available for routing IPX over ISL links in VLANs.
Figure 14. Configurable IPX Encapsulations Routed over ISL in VLAN
Configurations
VLAN 20 Configuration
ipx routing
interface FastEthernet 2/0
no shutdown
interface FastEthernet 2/0.20
encapsulation isl 20
ipx network 20 encapsulation sap
The following example enables IPX routing on FDDI interfaces 0.2 and 0.3 with SDE. On FDDI interface 0.2, the encapsulation
type is SNAP. On FDDI interface 0.3, the encapsulation type is Novell’s FDDI_RAW.
The following is the configuration for the Catalyst 5000 switch with
the Token Ring switch module in slot 5. In this configuration, the Token Ring
port 1 is assigned to the TrCRF VLAN 40:
#vtp
set vtp domain trisl
set vtp mode server
set vtp v2 enable
#drip
set set tokenring reduction enable
set tokenring distrib-crf disable
#vlans
set vlan 999 name trbrf type trbrf bridge 0xe stp ieee
set vlan 200 name trcrf200 type trcrf parent 999 ring 0x64 mode srt
set vlan 40 name trcrf40 type trcrf parent 999 ring 0x1 mode srt
#add token port to trcrf 40
set vlan 40 5/1
set trunk 1/2 on
VIP Distributed Switching over ISL Configuration Example
The figure below shows a topology in which Catalyst VLAN switches are
connected to routers forwarding traffic from a number of ISL VLANs. With the
VIP distributed ISL capability in the Cisco 7500 series router, each VIP card
can route ISL-encapsulated VLAN IP traffic. The inter-VLAN routing capacity is
increased linearly by the packet-forwarding capability of each VIP card.
Figure 16. VIP Distributed ISL VLAN Traffic
In the figure above, the VIP cards forward the traffic between ISL
VLANs or any other routing interface. Traffic from any VLAN can be routed to
any of the other VLANs, regardless of which VIP card receives the traffic.
These commands show the configuration for each of the VLANs shown in
the figure above:
interface FastEthernet1/0/0
ip address 10.1.1.1 255.255.255.0
ip route-cache distributed
full-duplex
interface FastEthernet1/0/0.1
ip address 10.1.1.1 255.255.255.0
encapsulation isl 1
interface FastEthernet1/0/0.2
ip address 10.1.2.1 255.255.255.0
encapsulation isl 2
interface FastEthernet1/0/0.3
ip address 10.1.3.1 255.255.255.0
encapsulation isl 3
interface FastEthernet1/1/0
ip route-cache distributed
full-duplex
interface FastEthernet1/1/0.1
ip address 172.16.1.1 255.255.255.0
encapsulation isl 4
interface Fast Ethernet 2/0/0
ip address 10.1.1.1 255.255.255.0
ip route-cache distributed
full-duplex
interface FastEthernet2/0/0.5
ip address 10.2.1.1 255.255.255.0
encapsulation isl 5
interface FastEthernet2/1/0
ip address 10.3.1.1 255.255.255.0
ip route-cache distributed
full-duplex
interface FastEthernet2/1/0.6
ip address 10.4.6.1 255.255.255.0
encapsulation isl 6
interface FastEthernet2/1/0.7
ip address 10.4.7.1 255.255.255.0
encapsulation isl 7
XNS Routing over ISL Configuration Example
To configure routing of the XNS protocol over ISL trunks, you need to define ISL as the encapsulation type. This example shows
XNS configured to be routed over an ISL trunk:
To configure routing of the CLNS protocol over ISL trunks, you need to define ISL as the encapsulation type. This example
shows CLNS configured to be routed over an ISL trunk:
The figure below shows AppleTalk being routed between different ISL
and IEEE 802.10 VLAN encapsulating subinterfaces.
Figure 17. Routing AppleTalk over VLAN encapsulations
As shown in the figure above, AppleTalk traffic is routed to and from
switched VLAN domains 3, 4, 100, and 200 to any other AppleTalk routing
interface. This example shows a sample configuration file for the Cisco 7500
series router with the commands entered to configure the network shown in the
figure above.
The following example configures VLAN ISL or IEEE 802.10 routing:
ipx routing
appletalk routing
!
interface Ethernet 1
ip address 10.1.1.1 255.255.255.0
appletalk cable-range 1-1 1.1
appletalk zone 1
ipx network 10 encapsulation snap
!
router igrp 1
network 10.1.0.0
!
end
!
#Catalyst5000
!
set VLAN 110 2/1
set VLAN 120 2/2
!
set trunk 1/1 110,120
# if 802.1Q, set trunk 1/1 nonegotiate 110, 120
!
end
!
ipx routing
appletalk routing
!
interface FastEthernet 1/1.110
encapsulation isl 110
!if 802.1Q, encapsulation dot1Q 110
ip address 10.1.1.2 255.255.255.0
appletalk cable-range 1.1 1.2
appletalk zone 1
ipx network 110 encapsulation snap
!
interface FastEthernet 1/1.120
encapsulation isl 120
!if 802.1Q, encapsulation dot1Q 120
ip address 10.2.1.2 255.255.255.0
appletalk cable-range 2-2 2.2
appletalk zone 2
ipx network 120 encapsulation snap
!
router igrp 1
network 10.1.0.0
network 10.2.1.0.0
!
end
!
ipx routing
appletalk routing
!
interface Ethernet 1
ip address 10.2.1.3 255.255.255.0
appletalk cable-range 2-2 2.3
appletalk zone 2
ipx network 120 encapsulation snap
!
router igrp 1
network 10.2.0.0
!
end
VLAN IEEE 802.1Q Bridging Example
The following examples configures IEEE 802.1Q bridging:
interface FastEthernet4/0
no ip address
no ip route-cache
half-duplex
!
interface FastEthernet4/0.100
encapsulation dot1Q 100
no ip route-cache
bridge-group 1
!
interface FastEthernet4/0.200
encapsulation dot1Q 200 native
no ip route-cache
bridge-group 2
!
interface FastEthernet4/0.300
encapsulation dot1Q 1
no ip route-cache
bridge-group 3
!
interface FastEthernet10/0
no ip address
no ip route-cache
half-duplex
!
interface FastEthernet10/0.100
encapsulation dot1Q 100
no ip route-cache
bridge-group 1
!
interface Ethernet11/3
no ip address
no ip route-cache
bridge-group 2
!
interface Ethernet11/4
no ip address
no ip route-cache
bridge-group 3
!
bridge 1 protocol ieee
bridge 2 protocol ieee
bridge 3 protocol ieee
VLAN IEEE 802.1Q IRB Example
The following examples configures IEEE 802.1Q integrated routing and bridging:
ip cef
appletalk routing
ipx routing 0060.2f27.5980
!
bridge irb
!
interface TokenRing3/1
no ip address
ring-speed 16
bridge-group 2
!
interface FastEthernet4/0
no ip address
half-duplex
!
interface FastEthernet4/0.100
encapsulation dot1Q 100
bridge-group 1
!
interface FastEthernet4/0.200
encapsulation dot1Q 200
bridge-group 2
!
interface FastEthernet10/0
ip address 10.3.1.10 255.255.255.0
half-duplex
appletalk cable-range 200-200 200.10
appletalk zone irb
ipx network 200
!
interface Ethernet11/3
no ip address
bridge-group 1
!
interface BVI 1
ip address 10.1.1.11 255.255.255.0
appletalk cable-range 100-100 100.11
appletalk zone bridging
ipx network 100
!
router rip
network 10.0.0.0
network 10.3.0.0
!
bridge 1 protocol ieee
bridge 1 route appletalk
bridge 1 route ip
bridge 1 route ipx
bridge 2 protocol ieee
!
Configuring IEEE 802.1Q-in-Q VLAN Tag Termination Example
Some ambiguous subinterfaces can use the
any keyword for the inner VLAN ID
specification. The
any keyword represents any inner VLAN ID that
is not explicitly configured on any other interface. In the following example,
seven subinterfaces are configured with various outer and inner VLAN IDs.
Note
The
any keyword can be configured on only one
subinterface of a specified physical interface and outer VLAN ID.
The table below shows which subinterfaces are mapped to different
values of the outer and inner VLAN ID on Q-in-Q frames that come in on Gigabit
Ethernet interface 1/0/0.
Table 2. Subinterfaces Mapped to Outer and Inner VLAN IDs for GE Interface
1/0/0
The table below shows the changes made to the table for the outer
VLAN ID of 200. Notice that subinterface 1/0/0.7 configured with the
any keyword now has new inner VLAN ID
mappings.
Table 3. Subinterfaces Mapped to Outer and Inner VLAN IDs for GE Interface
1/0/0--Changes Resulting from Configuring GE Subinterface 1/0/0.8
Outer VLAN ID
Inner VLAN ID
Subinterface mapped to
200
1 through 49
GigabitEthernet1/0/0.7
200
50
GigabitEthernet1/0/0.5
200
51 through 199
GigabitEthernet1/0/0.7
200
200 through 600
GigabitEthernet1/0/0.8
200
601 through 899
GigabitEthernet1/0/0.7
200
900 through 999
GigabitEthernet1/0/0.8
200
1000 through 2000
GigabitEthernet1/0/0.6
200
2001 through 2999
GigabitEthernet1/0/0.7
200
3000 through 4000
GigabitEthernet1/0/0.6
200
4001 through 4095
GigabitEthernet1/0/0.7
Additional References
The following sections provide references related to the Managed LAN Switch feature.
Related Documents
Related Topic
Document Title
IP LAN switching commands: complete command syntax, command mode, defaults, usage guidelines, and examples
No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.
--
Technical Assistance
Description
Link
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and
resolving technical issues with Cisco products and technologies.
To receive security and technical information about your products, you can subscribe to various services, such as the Product
Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.
Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 4. Feature Information for Routing Between VLANs
Encapsulating IEEE 802.1Q VLAN tags within 802.1Q enables service providers to use a single VLAN to support customers who
have multiple VLANs. The IEEE 802.1Q-in-Q VLAN Tag Termination feature on the subinterface level preserves VLAN IDs and keeps
traffic in different customer VLANs segregated.
Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation
The IEEE 802.1Q protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. The IEEE
802.1Q standard is extremely restrictive to untagged frames. The standard provides only a per-port VLANs solution for untagged
frames. For example, assigning untagged frames to VLANs takes into consideration only the port from which they have been received.
Each port has a parameter called a
permanent virtual identification (Native VLAN) that specifies the VLAN assigned to receive untagged frames.
In Cisco IOS XE Release 3.8(S), support was added for the Cisco ISR 4400 Series Routers.
In Cisco IOS XE Release 3.9(S), support was added for the Cisco CSR 1000V Series Routers.
Configuring Routing Between VLANs with Inter-Switch Link Encapsulation
ISL is a Cisco protocol for interconnecting multiple switches and maintaining VLAN information as traffic goes between switches.
ISL provides VLAN capabilities while maintaining full wire speed performance on Fast Ethernet links in full- or half-duplex
mode. ISL operates in a point-to-point environment and will support up to 1000 VLANs. You can define virtually as many logical
networks as are necessary for your environment.
Configuring Routing Between VLANs with IEEE 802.10 Encapsulation
AppleTalk can be routed over VLAN subinterfaces using the ISL or IEEE 802.10 VLANs feature that provides full-feature Cisco
IOS software AppleTalk support on a per-VLAN basis, allowing standard AppleTalk capabilities to be configured on VLANs.
Using the VLAN Range feature, you can group VLAN subinterfaces together so that any command entered in a group applies to
every subinterface within the group. This capability simplifies configurations and reduces command parsing.
In Cisco IOS Release 12.0(7)XE, the
interface range command was introduced.
The
interface range command was integrated into Cisco IOS Release 12.1(5)T.
In Cisco IOS Release 12.2(2)DD, the
interface range command was expanded to enable configuration of subinterfaces.
Theinterface range command was integrated into Cisco IOS Release 12.2(4)B.
The VLAN Range feature was integrated into Cisco IOS Release 12.2(8)T.
This VLAN Range feature was integrated into Cisco IOS Release 12.2(13)T.
256+ VLANS
12.1(2)E, 12.2(8)T
Cisco IOS XE 3.8(S)
Cisco IOS XE 3.9(S)
The 256+ VLAN feature enables a device to route
more than 256 VLAN interfaces. This feature requires the
MSFC2. The routed VLAN interfaces can be chosen from any of the
VLANs supported on the device. Catalyst switches can support up to
4096 VLANs.
If MSFC is used, up
to 256 VLANs can be routed, but this can be selected from any
VLANs supported on the device.
In Cisco IOS XE Release 3.8(S), support was added for the Cisco ISR 4400 Series Routers.
In Cisco IOS XE Release 3.9(S), support was added for the Cisco CSR 1000V Series Routers.
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