The IEEE 802.3 protocol standards define the physical layer and MAC sublayer of the data link layer of wired Ethernet. IEEE 802.3 uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access at various speeds over various physical media. The IEEE 802.3 standard covers 10 Mbps Ethernet. Extensions to the IEEE 802.3 standard specify implementations for 40-Gigabit Ethernet and 100-Gigabit Ethernet.

Under the International Standards Organization’s Open Systems Interconnection (OSI) model, Ethernet is fundamentally a Layer 2 protocol. 10-Gigabit Ethernet uses the IEEE 802.3 Ethernet MAC protocol, the IEEE 802.3 Ethernet frame format, and the minimum and maximum IEEE 802.3 frame size. 10-Gbps Ethernet conforms to the IEEE 802.3ae protocol standards.

Just as 1000BASE-X and 1000BASE-T (Gigabit Ethernet) remained true to the Ethernet model, 10-Gigabit Ethernet continues the natural evolution of Ethernet in speed and distance. Because it is a full-duplex only and fiber-only technology, it does not need the carrier-sensing multiple-access with the CSMA/CD protocol that defines slower, half-duplex Ethernet technologies. In every other respect, 10-Gigabit Ethernet remains true to the original Ethernet model.

IEEE 802.3ba is supported on the Cisco 1-Port 100-Gigabit Ethernet PLIM beginning in Cisco IOS XR 7.0.11.

On the router, a trunk interface can be either a Layer 2 or Layer 3 interface. A Layer 2 interface is configured using the interface command with the l2transport keyword. When the l2transport keyword is not used, the interface is a Layer 3 interface. Subinterfaces are configured as Layer 2 or Layer 3 subinterface in the same way.

A Layer 3 trunk interface or subinterface is a routed interface and can be assigned an IP address. Traffic sent on that interface is routed.

A Layer 2 trunk interface or subinterface is a switched interface and cannot be assigned an IP address. A Layer 2 interface must be connected to an L2VPN component. Once it is connected, it is called an access connection.

Subinterfaces can only be created under a Layer 3 trunk interface. Subinterfaces cannot be created under a Layer 2 trunk interface.

A Layer 3 trunk interface can have any combination of Layer 2 and Layer 3 interfaces.

The following example shows an attempt to configure a subinterface under an Layer 2 trunk and the commit errors that occur. It also shows an attempt to change the Layer 2 trunk interface to an Layer 3 interface and the errors that occur because the interface already had an IP address assigned to it.

RP/0/RP0/CPU0:router# config
Mon Sep 21 12:05:33.142 EDT
RP/0/RP0/CPU0:router(config)# interface HundredGigE0/5/0/0
RP/0/RP0/CPU0:router(config-if)# ipv4 address 10.0.0.1/24
RP/0/RP0/CPU0:router(config-if)# commit
RP/0/RP0/CPU0:Sep 21 12:05:57.824 : config[65794]: %MGBL-CONFIG-6-DB_COMMIT : Configuration committed by user 'root'. Use 'show configuration commit changes 1000000160' to view the changes.
RP/0/RP0/CPU0:router(config-if)# end
RP/0/RP0/CPU0:Sep 21 12:06:01.890 : config[65794]: %MGBL-SYS-5-CONFIG_I : Configured from console by root
RP/0/RP0/CPU0:router# show run | begin HundredGigE0/5/0/0
Mon Sep 21 12:06:19.535 EDT
Building configuration...
interface HundredGigE0/5/0/0
 ipv4 address 10.0.0.1 255.255.255.0
 negotiation auto
!
interface HundredGigE0/5/0/1
 shutdown
!
RP/0/RP0/CPU0:router#
RP/0/RP0/CPU0:router#
RP/0/RP0/CPU0:router# conf
Mon Sep 21 12:08:07.426 EDT
RP/0/RP0/CPU0:router(config)# interface HundredGigE0/5/0/0 l2transport
RP/0/RP0/CPU0:router(config-if-l2)# commit

% Failed to commit one or more configuration items during a pseudo-atomic operation. All changes made have been reverted. Please issue 'show configuration failed' from this session to view the errors
RP/0/RP0/CPU0:router(config-if-l2)# no ipv4 address
RP/0/RP0/CPU0:router(config-if)# commit
RP/0/RP0/CPU0:Sep 21 12:08:33.686 : config[65794]: %MGBL-CONFIG-6-DB_COMMIT : Configuration committed by user 'root'. Use 'show configuration commit changes 1000000161' to view the changes.
RP/0/RP0/CPU0:router(config-if)# end
RP/0/RP0/CPU0:Sep 21 12:08:38.726 : config[65794]: %MGBL-SYS-5-CONFIG_I : Configured from console by root
RP/0/RP0/CPU0:router#
RP/0/RP0/CPU0:router# show run interface HundredGigE0/5/0/0
Mon Sep 21 12:09:02.471 EDT
interface HundredGigE0/5/0/0
 negotiation auto
 l2transport
 !
!
RP/0/RP0/CPU0:router#
RP/0/RP0/CPU0:router# conf
Mon Sep 21 12:09:08.658 EDT
RP/0/RP0/CPU0:router(config)# interface HundredGigE0/5/0/0.0
                                                  ^
RP/0/RP0/CPU0:router(config)# interface HundredGigE0/5/0/0.0
RP/0/RP0/CPU0:router(config-subif)# commit

% Failed to commit one or more configuration items during a pseudo-atomic operation. All changes made have been reverted. Please issue 'show configuration failed' from this session to view the errors
RP/0/RP0/CPU0:router(config-subif)#
RP/0/RP0/CPU0:router(config-subif)# interface HundredGigE0/5/0/0
RP/0/RP0/CPU0:router(config-if)# no l2transport
RP/0/RP0/CPU0:router(config-if)# interface HundredGigE0/5/0/0.0
RP/0/RP0/CPU0:router(config-subif)# encapsulation dot1q 99
RP/0/RP0/CPU0:router(config-subif)# ipv4 address 11.0.0.1/24
RP/0/RP0/CPU0:router(config-subif)# interface HundredGigE0/5/0/0.1 l2transport
RP/0/RP0/CPU0:router(config-subif)# encapsulation dot1q 700
RP/0/RP0/CPU0:router(config-subif)# commit
RP/0/RP0/CPU0:Sep 21 12:11:45.896 : config[65794]: %MGBL-CONFIG-6-DB_COMMIT : Configuration committed by user 'root'. Use 'show configuration commit changes 1000000162' to view the changes.
RP/0/RP0/CPU0:router(config-subif)# end
RP/0/RP0/CPU0:Sep 21 12:11:50.133 : config[65794]: %MGBL-SYS-5-CONFIG_I : Configured from console by root
RP/0/RP0/CPU0:router#
RP/0/RP0/CPU0:router# show run | b HundredGigE0/5/0/0
Mon Sep 21 12:12:00.248 EDT
Building configuration...
interface HundredGigE0/5/0/0
 negotiation auto
!
interface HundredGigE0/5/0/0.0
 ipv4 address 11.0.0.1 255.255.255.0
 encapsulation dot1q 99
!
interface HundredGigE0/5/0/0.1 l2transport
 encapsulation dot1q 700
!
interface HundredGigE0/5/0/1
 shutdown
!

All subinterfaces must have unique encapsulation statements, so that the router can send incoming packets and frames to the correct subinterface. If a subinterface does not have an encapsulation statement, the router will not send any traffic to it.

In Cisco IOS XR, an Ethernet Flow Point (EFP) is implemented as a Layer 2 subinterface, and consequently, a Layer 2 subinterface is often called an EFP.

A Layer 2 trunk interface can be used as an access connection. However, a Layer 2 trunk interface is not an EFP because an EFP, by definition, is a substream of an overall stream of traffic.

Cisco IOS XR also has other restrictions on what can be configured as a Layer 2 or Layer 3 interface. Certain configuration blocks only accept Layer 3 and not Layer 2. For example, OSPF only accepts Layer 3 trunks and subinterface. Refer to the appropriate Cisco IOS XR configuration guide for other restrictions.

Beginning in Cisco IOS XR Release 7.2.12, the router adds support for basic counters for performance monitoring on Layer 2 subinterfaces. This section provides a summary of the new support for Layer 2 interface counters.

The interface basic-counters keyword has been added to support a new entity for performance statistics collection and display on Layer 2 interfaces in the following commands:

• performance-mgmt statistics interface basic-counters

• performance-mgmt threshold interface basic-counters

• performance-mgmt apply statistics interface basic-counters

• performance-mgmt apply threshold interface basic-counters

• performance-mgmt apply monitor interface basic-counters

• show performance-mgmt monitor interface basic-counters

• show performance-mgmt statistics interface basic-counters

The performance-mgmt threshold interface basic-counters command supports the following attribute values for Layer 2 statistics, which also appear in the show performance-mgmt statistics interface basic-counters and show performance-mgmt monitor interface basic-counters command:

The following additional performance management enhancements are included in Cisco IOS XR Release 7.0.11:

• You can retain performance management history statistics across a process restart or route processor (RP) failover using the new history-persistent keyword option for the performance-mgmt statistics interface command.

• You can save performance management statistics to a local file using the performance-mgmt resources dump local command.

• You can filter performance management instances by defining a regular expression group (performance-mgmt regular-expression command), which includes multiple regular expression indices that specify strings to match. You apply a defined regular expression group to one or more statistics or threshold templates in the performance-mgmt statistics interface or performance-mgmt thresholds interface commands.

LLDP frames use the IEEE 802.3 format, which consists of the following fields:

• Destination address (6 bytes)—Uses a multicast address of 01-80-C2-00-00-0E.

• Source address (6 bytes)—MAC address of the sending device or port.

• LLDP Ethertype (2 bytes)—Uses 88-CC.

• LLDP PDU (1500 bytes)—LLDP payload consisting of TLVs.

• FCS (4 bytes)—Cyclic Redundancy Check (CRC) for error checking.

LLDP TLVs carry the information about neighboring devices within the LLDP PDU using the following basic format:

• TLV Header (16 bits), which includes the following fields:

  • TLV Type (7 bits)

  • TLV Information String Length (9 bits)

• TLV Information String (0 to 511 bytes)

LLDP is a one-way protocol. The basic operation of LLDP consists of a device enabled for transmit of LLDP information sending periodic advertisements of information in LLDP frames to a receiving device.

Devices are identified using a combination of the Chassis ID and Port ID TLVs to create an MSAP (MAC Service Access Point). The receiving device saves the information about a neighbor in a remote lldp cache for a certain amount of time as specified in the TTL TLV received from the neighbor, before aging and removing the information.

LLDP supports the following additional operational characteristics:

• LLDP can operate independently in transmit or receive modes. On global lldp enablement, the default mode is to operate in both transmit and receive modes.

• LLDP operates as a slow protocol with transmission speeds not greater than one frame per five seconds.

• LLDP packets are sent when the following occurs:

  • The packet update frequency specified by the lldp timer command is reached. The default is 30 seconds.

  • When a change in the values of the managed objects occurs from the local system’s LLDP MIB.

  • When LLDP is activated on an interface (3 frames are sent upon activation similar to CDP).

• When an LLDP frame is received, the LLDP remote services and PTOPO MIBs are updated with the information in the TLVs.

• LLDP supports the following actions on these TLV characteristics:

  • Interprets a neighbor TTL value of 0 as a request to automatically purge the information of the transmitting device. These shutdown LLDPDUs are typically sent prior to a port becoming inoperable.

  • An LLDP frame with a malformed mandatory TLV is dropped.

  • A TLV with an invalid value is ignored.

  • A copy of an unknown organizationally-specific TLV is maintained if the TTL is non-zero, for later access through network management.

The router supports the following LLDP functions:

• IPv4 and IPv6 management addresses—In general, both IPv4 and IPv6 addresses will be advertised if they are available, and preference is given to the address that is configured on the transmitting interface.

  If the transmitting interface does not have a configured address, then the system populates the TLV with an address from another interface. The advertised LLDP IP address is implemented according to the following priority order of IP addresses for interfaces on the router:

  • Locally configured address on the transmitting interface

  • MgmtEth0/RSP0RP0/CPU0/0

  • MgmtEth0/RSP0RP0/CPU0/1

  • MgmtEth0/RSP1RP1/CPU0/0

  • MgmtEth0/RSP1RP1/CPU0/1

  • Loopback interfaces

    There are some differences between IPv4 and IPv6 address management in LLDP:

• For IPv4, as long as the IPv4 address is configured on an interface, it can be used as an LLDP management address.

• For IPv6, after the IPv6 address is configured on an interface, the interface status must be Up and pass the DAD (Duplicate Address Detection) process before it is can be used as an LLDP management address.

• LLDP is supported for the nearest physically attached, non-tunneled neighbors.

• LLDP is supported for Ethernet interfaces, L3 subinterfaces, bundle interfaces, and L3 bundle subinterfaces.

• LLDP snoop is supported on L2 interfaces, when the incoming (RX) traffic is enabled and outgoing (TX) traffic is disabled.

The following LLDP functions are not supported on the router:

• LLDP-MED organizationally unique extension—However, interoperability still exists between other devices that do support this extension.

• Tunneled neighbors, or neighbors more than one hop away.

• LLDP TLVs cannot be disabled on a per-interface basis; However, certain optional TLVs can be disabled globally.

• LLDP SNMP trap lldpRemTablesChange.

This table shows the values of the LLDP default configuration on the router. To change the default settings, use the LLDP global configuration and LLDP interface configuration commands.

RP/0/RSP0/CPU0:ios(config)# int HundredGigE 0/2/0/0
RP/0/RSP0/CPU0:ios(config-if)# no sh
RP/0/RSP0/CPU0:ios(config-if)#commit
RP/0/RSP0/CPU0:ios(config-if)#lldp ?
RP/0/RSP0/CPU0:ios(config-if)#lldp enable
RP/0/RSP0/CPU0:ios(config-if)#commit

Running configuration

RP/0/RSP0/CPU0:ios#sh running-config  
Wed Jun 27 12:40:21.274 IST
Building configuration...
!! IOS XR Configuration 0.0.0
!! Last configuration change at Wed Jun 27 00:59:29 2018 by UNKNOWN
!
interface HundredGigE0/1/0/0
 shutdown
!
interface HundredGigE0/1/0/1
 shutdown
!
interface HundredGigE0/1/0/2
 shutdown
!
interface HundredGigE0/2/0/0
 Shutdown
!
interface HundredGigE0/2/0/1
 shutdown
!
interface HundredGigE0/2/0/2
 shutdown
!
end

Verification

Verifying the config
==================
RP/0/RSP0/CPU0:ios#sh lldp interface <===== LLDP enabled only on GigEth0/2/0/0
Wed Jun 27 12:43:26.252 IST


HundredGigE0/2/0/0:
        Tx: enabled
        Rx: enabled
        Tx state: IDLE
        Rx state: WAIT FOR FRAME
RP/0/RSP0/CPU0:ios# 

RP/0/RSP0/CPU0:ios# show lldp neighbors 
Wed Jun 27 12:44:38.977 IST
Capability codes:
        (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device
        (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other

Device ID       Local Intf          Hold-time  Capability     Port ID
ios             Gi0/2/0/0           120        R               Gi0/2/0/0       <====== LLDP enabled only on GigEth0/2/0/0 and neighborship seen for the same.

Total entries displayed: 1

RP/0/RSP0/CPU0:ios#

This section describes how you can verify the LLDP configuration both globally and for a particular interface.