IP Addresses and Services Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 7.2.x
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The Network Stack IPv4
and IPv6 features are used to configure and monitor Internet Protocol Version 4
(IPv4) and Internet Protocol Version 6 (IPv6).
Restrictions
In any Cisco IOS XR
software release with IPv6 support, multiple IPv6 global addresses can be
configured on an interface. However, multiple IPv6 link-local addresses on an
interface are not supported.
Implementing Fallback VRF
Virtual Routing and Forwarding (VRF) is an IP technology that allows multiple instances of a routing table to coexist simultaneously
on the same router. Because the routing instances are independent, the same IP addresses can be used without conflict.
If the destination prefix of a data packet does not match any route in the configured VRF, a default route is identified from
the global routing table. However, using a default route needs an explicit next hop and that may not be efficient. A better
option is to configure a fallback VRF route. If the destination does not have a match in the VRF table, the fallback VRF table
is used. The fallback VRF can either be the global routing table or a non-global VRF table.
Restrictions
The following restrictions apply if you configure a fallback VRF route:
You can configure only one fallback VRF route for each address family of each primary VRF.
Ping, traceroute, or any slow path application is not supported on fallback VRF because there is no support for LPTS receive
trap.
Only 255 VRFs and 1 global table are supported ion the router.
If you configure a static default route to a VRF, the static default route takes precedence over the fallback VRF. If you
configure the default route for a VRF, the global routing table is used for a route lookup. The default route is always directed
to the configured next hop.
If a route lookup for a packet fails in the primary VRF, the packet is recycled to do route lookup in the fallback VRF. Therefore,
the routing performance of the packet goes down by up to 50 percent.
If you configure both ACL-based forwarding (ABF) VRF redirect and VRF fallback for a packet, then the packet is recycled twice.
Therefore, the routing performance of the packet goes down by up to 33 percent.
If a route for a packet is found in the fallback VRF, only the Glean IPv4 and Glean IPv6 adjacency packets are punted successfully.
In a looped configuration, if the route for a packet is not found in both the primary and fallback VRF, the packet loops in
the recycle path. Eventually, the packet is dropped in the recycle egress queue. The recycle queue is of highest priority.
Therefore, if there is a high rate of looped traffic, other good recycled packets may be dropped.
Network Stack IPv4
and IPv6 Exceptions
The Network Stack
feature in the
Cisco IOS XR software has the following exceptions:
In
Cisco IOS XR software, the
clear ipv6
neighbors and
show ipv6
neighbors
commands include the
locationnode-id keyword. If a location is specified, only the neighbor
entries in the specified location are displayed.
The
ipv6 nd
scavenge-timeout command sets the lifetime for neighbor entries in the stale
state. When the scavenge-timer for a neighbor entry expires, the entry is
cleared.
In
Cisco IOS XR software, the
show ipv4
interface and
show ipv6
interface
commands include the
locationnode-id keyword. If a location is specified, only the interface
entries in the specified location are displayed.
Cisco IOS XR software allows conflicting IP address entries at the time of configuration. If an IP address conflict exists between two interfaces
that are active, Cisco IOS XR software brings down the interface according to the configured conflict policy, the default
policy being to bring down the higher interface instance.
For example, if HundredGigE 0/0/0/1 conflicts with HundredGigE 0/0/0/2, then the IPv4 protocol on HundredGigE 0/0/0/2, is brought down and IPv4 remains active on HundredGigE 0/0/0/1.
IPv4 and IPv6
Functionality
When
Cisco IOS XR software is configured with both an IPv4 and an IPv6 address, the interface
can send and receive data on both IPv4 and IPv6 networks.
The architecture of
IPv6 has been designed to allow existing IPv4 users to make the transition
easily to IPv6 while providing services such as end-to-end security, quality of
service (QoS), and globally unique addresses. The larger IPv6 address space
allows networks to scale and provide global reachability. The simplified IPv6
packet header format handles packets more efficiently. IPv6 prefix aggregation,
simplified network renumbering, and IPv6 site multihoming capabilities provide
an IPv6 addressing hierarchy that allows for more efficient routing. IPv6
supports widely deployed routing protocols such as Open Shortest Path First
(OSPF), and multiprotocol Border Gateway Protocol (BGP).
The IPv6 neighbor
discovery (nd) process uses Internet Control Message Protocol (ICMP) messages
and solicited-node multicast addresses to determine the link-layer address of a
neighbor on the same network (local link), verify the reachability of a
neighbor, and keep track of neighboring routers.
IPv6 for Cisco IOS XR Software
IPv6, formerly named IPng (next generation) is the latest version of the Internet Protocol (IP). IP is a packet-based protocol
used to exchange data, voice, and video traffic over digital networks. IPv6 was proposed when it became clear that the 32-bit
addressing scheme of IP version 4 (IPv4) was inadequate to meet the demands of Internet growth. After extensive discussion,
it was decided to base IPng on IP but add a much larger address space and improvements such as a simplified main header and
extension headers. IPv6 is described initially in RFC 2460, Internet Protocol, Version 6 (IPv6) Specification issued by the Internet Engineering Task Force (IETF). Further RFCs describe the architecture and services supported by IPv6.
How to Implement Network Stack IPv4 and IPv6
This section contains the following procedures:
Configuring IPv4
Addressing
A basic and required
task for configuring IP is to assign IPv4 addresses to network interfaces.
Doing so enables the interfaces and allows communication with hosts on those
interfaces using IPv4. An IP address identifies a location to which IP
datagrams can be sent. An interface can have one primary IP address and
multiple secondary addresses. Packets generated by the software always use the
primary IPv4 address. Therefore, all networking devices on a segment should
share the same primary network number.
Associated with this
task are decisions about subnetting and masking the IP addresses. 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
subnet mask.
Note
Cisco supports only network masks that use contiguous bits that are flush left against the network field.
Configuration
Example
An IPv4 address of 192.168.1.27 and a network mask of "/8" is assigned to the interface HundredGigE 0/0/0/1.
Note
The network mask
can be a four-part dotted decimal address. For example, 255.0.0.0 indicates
that each bit equal to 1 means the corresponding address bit belongs to the
network address. The network mask can be indicated as a slash (/) and a number-
a prefix length. The prefix length is a decimal value that indicates how many
of the high-order contiguous bits of the address comprise the prefix (the
network portion of the address). A slash must precede the decimal value, and
there is no space between the IP address and the slash.
Verify that the
HundredGigE interface is active and IPv4 is enabled.
Router# show ipv4 interface HundredGigE0/0/0/1
interface HundredGigE0/0/0/1 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.168.1.27/8
MTU is 1514 (1500 is available to IP)
Helper address is not set
Multicast reserved groups joined: 224.0.0.2 224.0.0.1
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000
Associated
Commands
ipv4 address
show ipv4 interface
Configuring IPv6
Addressing
IPv6 addresses are configured to
individual router interfaces in order to enable the forwarding of IPv6 traffic
globally on the router. By default, IPv6 addresses are not configured.
Note
The
ipv6-prefix
argument in the
ipv6 address command must be in the form documented in RFC 2373 in which
the address is specified in hexadecimal using 16-bit values between colons.
The /prefix-length argument in the
ipv6 address command is a decimal value that indicates how many of the
high-order contiguous bits of the address comprise the prefix (the network
portion of the address) A slash must precede the decimal value.
The
ipv6-address argument in the
ipv6 address link-local command must be in the form documented in RFC 2373 where the
address is specified in hexadecimal using 16-bit values between colons.
IPv6 Multicast
Groups
An IPv6 address must
be configured on an interface for the interface to forward IPv6 traffic.
Configuring a global IPv6 address on an interface automatically configures a
link-local address and activates IPv6 for that interface.
Additionally, the
configured interface automatically joins the following required multicast
groups for that link:
Solicited-node
multicast group FF02:0:0:0:0:1:FF00::/104 for each unicast address assigned to
the interface
All-nodes
link-local multicast group FF02::1
All-routers
link-local multicast group FF02::2
Note
The
solicited-node multicast address is used in the neighbor discovery process.
Configuration
Example
An IPv6 address of 2001:0DB8:0:1::1/64 is assigned to the interface HundredGigE 0/0/0/1:
Verify that the
HundredGigE interface is active and IPv6 is enabled.
Router#show ipv6 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::c672:95ff:fea6:1c75
Global unicast address(es):
2001:db8:0:1::1, subnet is 2001:db8:0:1::/64
Joined group address(es): ff02::1:ff00:1 ff02::1:ffa6:1c75 ff02::2
ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
Associated
Commands
ipv6 address
interface
show ipv6 interface
Configuration
Example
An IPv6 address of 2001:0DB8:0:1::/64 is assigned to the interface HundredGigE 0/0/0/1. The eui-64 keyword configures site-local and global IPv6 addresses with an interface identifier (ID) in the low-order 64 bits of the
IPv6 address. Only the 64-bit network prefix for the address needs to be specified; the last 64 bits are automatically computed
from the interface ID.
Verify that the HundredGigE interface is active and IPv6 is enabled.
Router#show ipv6 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::c672:95ff:fea6:1c75
Global unicast address(es):
2001:db8:0:1:c672:95ff:fea6:1c75, subnet is 2001:db8:0:1::/64
Joined group address(es): ff02::1:ffa6:1c75 ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
Associated
Commands
ipv6 address
interface
show ipv6 interface
Configuration
Example
An IPv6 address of FE80::260:3EFF:FE11:6770 is assigned to the interface HundredGigE 0/0/0/1. The link-local keyword configures a link-local address on the interface that is used instead of the link-local address that
is automatically configured when IPv6 is enabled on the interface.
Verify that the
HundredGigE interface is active and IPv6 is enabled with link-local address.
Router#show ipv6 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::260:3eff:fe11:6770
Global unicast address(es):
2001:db8:0:1:260:3eff:fe11:6770, subnet is 2001:db8:0:1::/64
Joined group address(es): ff02::1:ff11:6770 ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
Associated
Commands
ipv6 address
interface
show ipv6 interface
Configuration
Example
Enable IPv6 processing on the interface HundredGigE 0/0/0/1; that has not been configured with an explicit IPv6 address.
Verify that the HundredGigE interface is active and IPv6 is enabled.
Router#show ipv6 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::c672:95ff:fea6:1c75
No global unicast address is configured
Joined group address(es): ff02::1:ffa6:1c75 ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
Associated
Commands
ipv6 enable
interface
show ipv6 interface
Configure Fallback VRF
You can configure a fallback VRF for a destination route that does not match any routes in the configured VRF.
The following example shows how to configure the fallback-vrf command for a destination that does not match any routes in the configured VRF.
To verify the fallback VRF details, use the showcefvrfvrf-nameipv4-prefix/ipv6-prefixhardwareegresslocationline-card-location command:
Router# show cef vrf vrf100 192.0.2.1 hardware egress location 0/1/CPU0
0.0.0.0/0, version 0, proxy default, internal 0x1200011 0x0 (ptr 0x8983f534) [1], 0x0 (0x894fa728), 0x0 (0x0)
Updated Mar 21 14:01:43.765
Prefix Len 0, traffic index 0, precedence n/a, priority 15
via 0.0.0.0/32, 0 dependencies, weight 0, class 0 [flags 0x0]
path-idx 0 NHID 0x0 [0x8871b168 0x0]
next hop VRF - 'vrf200', table - 0xe0000008
next hop 0.0.0.0/32
LEAF - HAL pd context :
sub-type : IPV4, ecd_marked:0, has_collapsed_ldi:0
collapse_bwalk_required:0, ecdv2_marked:0,
HW Walk:
Assigning Multiple
IP Addresses to Network Interfaces
The
Cisco IOS XR software supports multiple IP addresses (secondary addresses) per interface.
You can specify an unlimited number of secondary addresses. Secondary IP
addresses can be used in a variety of situations. The following are the most
common applications:
There might not be
enough host addresses for a particular network segment. For example, suppose
your subnetting allows up to 254 hosts per logical subnet, but on one physical
subnet you must have 300 host addresses. Using secondary IP addresses on the
routers or access servers allows you to have two logical subnets using one
physical subnet.
Many older
networks were built using Level 2 bridges, and were not subnetted. The
judicious use of secondary addresses can aid in the transition to a subnetted,
router-based network. Routers on an older, bridged segment can easily be made
aware that many subnets are on that segment.
Two subnets of a
single network might otherwise be separated by another network. You can create
a single network from subnets that are physically separated by another network
by using a secondary address. In these instances, the first network is
extended, or layered on top of the second network. Note
that a subnet cannot appear on more than one active interface of the router at
a time.
Note
If any router on a
network segment uses a secondary IPv4 address, all other routers on that same
segment must also use a secondary address from the same network or subnet.
Caution
Inconsistent use of
secondary addresses on a network segment can quickly cause routing loops.
Configuration
Example
A secondary IPv4
address of 192.168.1.27 is assigned to the Hundredgige interface-0/0/0/1.
Note: For IPv6, an
interface can have multiple IPv6 addresses without specifying the
secondary
keyword.
Router#show ipv4 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is unassigned
Secondary address 192.168.1.27/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Multicast reserved groups joined: 224.0.0.2 224.0.0.1
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000
Associated
Commands
ipv4 address
show ipv4 interface
Configuring IPv4 and
IPv6 Protocol Stacks
This task configures
an interface in a Cisco networking device to support both the IPv4 and IPv6
protocol stacks.
When an interface in a
Cisco networking device is configured with both an IPv4 and an IPv6 address,
the interface forwards both IPv4 and IPv6 traffic—the interface can send and
receive data on both IPv4 and IPv6 networks.
Configuration
Example
An IPv4 address of 192.168.99.1 and an IPv6 address of 2001:0DB8:c18:1::3/64 is configured on the interface HundredGigE 0/0/0/1.
Verify that the
HundredGigE interface is active and IPv4 and IPv6 are enabled.
Router#show ipv4 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.168.99.1/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Multicast reserved groups joined: 224.0.0.2 224.0.0.1
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000
Router#show ipv6 interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::c672:95ff:fea6:1c75
Global unicast address(es):
2001:db8:c18:1::3, subnet is 2001:db8:c18:1::/64
Joined group address(es): ff02::1:ff00:3 ff02::1:ffa6:1c75 ff02::2
ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
Associated
Commands
ipv4 address
ipv6 address
show ipv4 interface
show ipv6 interface
Enabling IPv4 Processing on an Unnumbered Interface
This section describes the process of enabling an IPv4 point-to-point
interface without assigning an explicit IP address to the interface. Whenever
the unnumbered interface generates a packet (for example, for a routing
update), it uses the address of the interface you specified as the source
address of the IP packet. It also uses the specified interface address in
determining which routing processes are sending updates over the unnumbered
interface. Restrictions are as follows:
Interfaces using High-Level Data Link Control (HDLC), PPP, and Frame
Relay encapsulations can be unnumbered. Serial interfaces using Frame Relay
encapsulation can also be unnumbered, but the interface must be a
point-to-point sub-interface.
You cannot use the
ping EXEC command to determine whether the interface is up,
because the interface has no IP address. The Simple Network Management Protocol
(SNMP) can be used to remotely monitor interface status.
You cannot support IP security options on an unnumbered interface.
If you are configuring Intermediate System-to-Intermediate System
(IS-IS) across a serial line, you should configure the serial interfaces as
unnumbered, which allows you to conform with RFC 1195, which states that IP
addresses are not required on each interface.
Configuration Example
Enables an IPv4 point-to-point interface without assigning an
explicit IP address to the interface.
Router#show interface HundredGigE0/0/0/1HundredGigE0/0/0/1 is up, line protocol is up
Interface state transitions: 5
Hardware is Hundredgige, address is 00e2.2a33.445b (bia 00e2.2a33.445b)
Layer 1 Transport Mode is LAN
Internet address is 10.0.0.2/32
MTU 1514 bytes, BW 10000000 Kbit (Max: 10000000 Kbit)
reliability 255/255, txload 194/255, rxload 0/255
Encapsulation ARPA,
Full-duplex, 10000Mb/s, link type is force-up
output flow control is off, input flow control is off
Carrier delay (up) is 10 msec
loopback not set,
Last link flapped 01:38:49
ARP type ARPA, ARP timeout 04:00:00
Last input 00:00:00, output 00:00:00
Last clearing of "show interface" counters 02:34:16
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 7647051000 bits/sec, 12254894 packets/sec
1061401410 packets input, 82789675614 bytes, 0 total input drops
0 drops for unrecognized upper-level protocol
Received 5 broadcast packets, 19429 multicast packets
0 runts, 0 giants, 0 throttles, 0 parity
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
76895885948 packets output, 6192569128048 bytes, 0 total output drops
Output 7 broadcast packets, 18916 multicast packets
0 output errors, 0 underruns, 0 applique, 0 resets
0 output buffer failures, 0 output buffers swapped out
2 carrier transitions
Router #show run int lo 0 interface Loopback0
ipv4 address 10.0.0.2 255.255.255.255
Associated Commands
ipv4 unnumbered
show interfaces
IPv4 ICMP Rate
Limiting
The IPv4 ICMP rate
limiting feature limits the rate that IPv4 ICMP destination unreachable
messages are generated. The Cisco IOS XR software maintains two timers: one for
general destination unreachable messages and one for DF destination unreachable
messages. Both share the same time limits and defaults. If the DF keyword is
not configured, the icmp ipv4 rate-limit unreachable command sets the time
values for DF destination unreachable messages. If the DF keyword is
configured, its time values remain independent from those of general
destination unreachable messages.
Configuration
Example
Limits the rate
that IPv4 ICMP destination unreachable messages are generated every 1000
millisecond.
The
DF keyword,
which is optional limits the rate at which ICMP destination unreachable
messages are sent when code 4 fragmentation is needed and Don't Fragment (DF)
is set, as specified in the IP header of the ICMP destination unreachable
message.
Router#show running-config | in icmp
Building configuration...
icmp ipv4 rate-limit unreachable DF 1000
icmp ipv4 rate-limit unreachable 1000
Verification
Router#show ipv4 interface HundredGigE0/0/0/2HundredGigE0/0/0/2 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.85.1.1/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Multicast reserved groups joined: 224.0.0.2 224.0.0.1 224.0.0.2
224.0.0.5 224.0.0.6
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000
The number of ICMP unreachable messages that were we sent or received
can be identified using the
show ipv4 traffic command.
Router# show ipv4 traffic
ICMP statistics:
Sent: 0 admin unreachable, 5 network unreachable
0 host unreachable, 0 protocol unreachable
0 port unreachable, 0 fragment unreachable
0 time to live exceeded, 0 reassembly ttl exceeded
0 echo request, 0 echo reply
0 mask request, 0 mask reply
0 parameter error, 0 redirects
5 total
Rcvd: 0 admin unreachable, 0 network unreachable
0 host unreachable, 0 protocol unreachable
0 port unreachable, 0 fragment unreachable
0 time to live exceeded, 0 reassembly ttl exceeded
0 echo request, 0 echo reply
0 mask request, 0 mask reply
0 redirect, 0 parameter error
0 source quench, 0 timestamp, 0 timestamp reply
0 router advertisement, 0 router solicitation
0 total, 0 checksum errors, 0 unknown
Associated
Commands
icmp ipv4 rate-limit unreachable
show ipv4 traffic
IPv6 ICMP Rate
Limiting
The IPv6 ICMP rate
limiting feature implements a token bucket algorithm for limiting the rate at
which IPv6 ICMP error messages are sent out on the network. The initial
implementation of IPv6 ICMP rate limiting defined a fixed interval between
error messages, but some applications, such as traceroute, often require
replies to a group of requests sent in rapid succession. The fixed interval
between error messages is not flexible enough to work with applications such as
traceroute and can cause the application to fail. Implementing a token bucket
scheme allows a number of tokens-representing the ability to send one error
message each-to be stored in a virtual bucket. The maximum number of tokens
allowed in the bucket can be specified, and for every error message to be sent,
one token is removed from the bucket. If a series of error messages is
generated, error messages can be sent until the bucket is empty. When the
bucket is empty of tokens, IPv6 ICMP error messages are not sent until a new
token is placed in the bucket. The token bucket algorithm does not increase the
average rate limiting time interval, and it is more flexible than the fixed
time interval scheme.
Configuration
Example
Configure the
interval for 50 milliseconds and the bucket size for 20 tokens, for IPv6 ICMP
error messages.
The milliseconds
argument specifies the interval between tokens being added to the bucket.
The optional
bucketsize argument defines the maximum number of tokens stored in the bucket.
Router#show running-config | in source rfc
Building configuration...
icmp ipv4 source rfc
Associated
Commands
Configuring IPARM
Conflict Resolution
This task sets the IP Address
Repository Manager (IPARM) address conflict resolution parameters:
Static Policy Resolution
Longest Prefix Address Conflict Resolution
Highest IP Address Conflict Resolution
Route-Tag Support for Connected Routes
Static Policy
Resolution
The static policy
resolution configuration prevents new address configurations from affecting
interfaces that are currently running.
Configuration
Example
Sets the conflict
policy to static, that is, prevents new interface addresses from affecting the
currently running interface.
Router#configure
Router(config)#ipv4 conflict-policy static*/For IPv6, use the ipv6 conflict-policy static command/*
Router(config)#commit
Running
Configuration
Router#show running-config | in ipv4 config
Building configuration...
!! IOS XR Configuration version = 6.0.0.26I
!! Last configuration change at Mon Dec 14 21:57:27 2015 by root
!
hostname sample-83
logging console debugging
username root
group root-lr
group test
secret 5 $1$d2NC$RbAdqdU7kw/eKJpMo/GJI1
!
cdp
ipv4 conflict-policy static
interface Loopback0
ipv4 address 1.1.1.1 255.255.255.255
!
…..
Verification
Router#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Te0/0/0/19 192.85.1.2/24 HundredGigE0/0/0/1 192.85.1.1/24 default
Forced down interface Up interface VRF
Associated
Commands
ipv4 conflict-policy
ipv6 conflict-policy
Longest Prefix
Address Conflict Resolution
This conflict
resolution policy attempts to give highest precedence to the IP address that
has the longest prefix length, that is, all addresses within the conflict-set
that do not conflict with the longest prefix address of the currently running
interface are allowed to run as well.
Router# configure
Router(config)# ipv4 conflict-policy longest-prefix*/For IPv6, use the ipv6 conflict-policy command*/
Router(config)# commit
Running
Configuration
Router# show running-config | in longest-prefix
Building configuration...
ipv4 conflict-policy longest-prefix
Verification
Router#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Te0/0/0/19 192.85.1.2/24 HundredGigE0/0/0/1 192.85.1.1/24 default
Forced down interface Up interface VRF
Highest IP Address
Conflict Resolution
This conflict
resolution policy attempts to give highest precedence to the IP address that
has the highest value, that is, the IP address with the highest value gets
precedence.
Configuration
Configures highest
IP address conflict resolution.
Router# configure
Router(config)#ipv4 conflict-policy highest-ip*/For IPv6, use the ipv6 conflict-policy highest-ip command/*
Router(config)#commit
Running
Configuration
Router#show running-config | in highest-ip
Building configuration...
ipv4 conflict-policy highest-ip
Verification
Router#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Te0/0/0/19 192.85.1.2/24 HundredGigE0/0/0/1 192.85.1.1/24 default
Forced down interface Up interface VRF
Route-Tag Support
for Connected Routes
Configuration
Example
The Route-Tag
Support for Connected Routes feature attaches a tag with all IPv4 and IPv6
addresses of an interface. The tag is propagated from the IPv4 and IPv6
management agents (MA) to the IPv4 and IPv6 address repository managers (ARM)
to routing protocols, thus enabling the user to control the redistribution of
connected routes by looking at the route tags, by using routing policy language
(RPL) scripts. This prevents the redistribution of some interfaces, by checking
for route tags in a route policy. The route tag feature is already available
for static routes and connected routes (interfaces) wherein the route tags are
matched to policies and redistribution can be prevented.
Specifies an IPv4 address 10.0.54.2/30 that has a route tag of 20 to the interface HundredGigE 0/0/0/1.
Router#show route 10.0.54.2
Routing entry for 10.0.54.2/32
Known via "local", distance 0, metric 0 (connected)
Tag 1899
Routing Descriptor Blocks
directly connected, via HundredGigE0/0/0/1
Route metric is 0
No advertising protos.
Associated
Commands
route-tag
Larger IPv6 Address
Space
The primary motivation for IPv6 is
the need to meet the anticipated future demand for globally unique IP
addresses. Applications such as mobile Internet-enabled devices (such as
personal digital assistants [PDAs], telephones, and cars), home-area networks
(HANs), and wireless data services are driving the demand for globally unique
IP addresses. IPv6 quadruples the number of network address bits from 32 bits
(in IPv4) to 128 bits, which provides more than enough globally unique IP
addresses for every networked device on the planet. By being globally unique,
IPv6 addresses inherently enable global reachability and end-to-end security
for networked devices, functionality that is crucial to the applications and
services that are driving the demand for the addresses. Additionally, the
flexibility of the IPv6 address space reduces the need for private addresses
and the use of Network Address Translation (NAT); therefore, IPv6 enables new
application protocols that do not require special processing by border routers
at the edge of networks.
IPv6 Address
Formats
IPv6 addresses are
represented as a series of 16-bit hexadecimal fields separated by colons (:) in
the format: x:x:x:x:x:x:x:x. Following are two examples of IPv6 addresses:
2001:0DB8:7654:3210:FEDC:BA98:7654:3210
2001:0DB8:0:0:8:800:200C:417A
It is common for IPv6
addresses to contain successive hexadecimal fields of zeros. To make IPv6
addresses less cumbersome, two colons (::) can be used to compress successive
hexadecimal fields of zeros at the beginning, middle, or end of an IPv6
address. (The colons represent successive hexadecimal fields of zeros.)
Table 1
lists compressed IPv6 address formats.
A double colon may be
used as part of the
ipv6-address argument when consecutive 16-bit values are denoted as zero. You
can configure multiple IPv6 addresses per interfaces, but only one link-local
address.
Note
Two colons (::) can
be used only once in an IPv6 address to represent the longest successive
hexadecimal fields of zeros.
The hexadecimal
letters in IPv6 addresses are not case-sensitive.
Table 1. Compressed IPv6
Address Formats
IPv6 Address
Type
Preferred
Format
Compressed
Format
Unicast
2001:0:0:0:0DB8:800:200C:417A
1080::0DB8:800:200C:417A
Multicast
FF01:0:0:0:0:0:0:101
FF01::101
Loopback
0:0:0:0:0:0:0:1
::1
Unspecified
0:0:0:0:0:0:0:0
::
The loopback address
listed in
Table 1
may be used by a node to send an IPv6 packet to itself. The loopback address in
IPv6 functions the same as the loopback address in IPv4 (127.0.0.1).
Note
The IPv6 loopback
address cannot be assigned to a physical interface. A packet that has the IPv6
loopback address as its source or destination address must remain within the
node that created the packet. IPv6 routers do not forward packets that have the
IPv6 loopback address as their source or destination address.
The unspecified
address listed in
Table 1
indicates the absence of an IPv6 address. For example, a newly initialized node
on an IPv6 network may use the unspecified address as the source address in its
packets until it receives its IPv6 address.
Note
The IPv6 unspecified
address cannot be assigned to an interface. The unspecified IPv6 addresses must
not be used as destination addresses in IPv6 packets or the IPv6 routing
header.
An IPv6 address
prefix, in the format
ipv6-prefix/prefix-length, can be used to represent bit-wise contiguous blocks of the
entire address space. The
ipv6-prefix argument must be in the form documented in RFC 2373, in which
the address is specified in hexadecimal using 16-bit values between colons. The
prefix length is a decimal value that indicates how many of the high-order
contiguous bits of the address compose the prefix (the network portion of the
address). For example, 2001:0DB8:8086:6502::/32 is a valid IPv6 prefix.
IPv6 Address Type:
Unicast
An IPv6 unicast address is an identifier for a single interface, on a
single node. A packet that is sent to a unicast address is delivered to the
interface identified by that address.
Cisco IOS XR software supports the following IPv6 unicast address types:
Global aggregatable address
Site-local address (proposal to remove by IETF)
Link-local address
IPv4-compatible IPv6 address
Aggregatable Global Address
An aggregatable global address is an IPv6 address from the aggregatable
global unicast prefix. The structure of aggregatable global unicast addresses
enables strict aggregation of routing prefixes that limits the number of
routing table entries in the global routing table. Aggregatable global
addresses are used on links that are aggregated upward through organizations,
and eventually to the Internet service providers (ISPs).
Aggregatable global IPv6 addresses are defined by a global routing
prefix, a subnet ID, and an interface ID. Except for addresses that start with
binary 000, all global unicast addresses have a 64-bit interface ID. The
current global unicast address allocation uses the range of addresses that
start with binary value 001 (2000::/3). This figure below shows the structure
of an aggregatable global address.
Addresses with a prefix of 2000::/3 (001) through E000::/3 (111) are
required to have 64-bit interface identifiers in the extended universal
identifier (EUI)-64 format. The Internet Assigned Numbers Authority (IANA)
allocates the IPv6 address space in the range of 2000::/16 to regional
registries.
The aggregatable global address typically consists of a 48-bit global
routing prefix and a 16-bit subnet ID or Site-Level Aggregator (SLA). In the
IPv6 aggregatable global unicast address format document (RFC 2374), the global
routing prefix included two other hierarchically structured fields named
Top-Level Aggregator (TLA) and Next-Level Aggregator (NLA).The IETF decided to
remove the TLS and NLA fields from the RFCs, because these fields are
policy-based. Some existing IPv6 networks deployed before the change might
still be using networks based on the older architecture.
A 16-bit subnet field called the subnet ID could be used by individual
organizations to create their own local addressing hierarchy and to identify
subnets. A subnet ID is similar to a subnet in IPv4, except that an
organization with an IPv6 subnet ID can support up to 65,535 individual
subnets.
An interface ID is used to identify interfaces on a link. The interface
ID must be unique to the link. It may also be unique over a broader scope. In
many cases, an interface ID is the same as or based on the link-layer address
of an interface. Interface IDs used in aggregatable global unicast and other
IPv6 address types must be 64 bits long and constructed in the modified EUI-64
format.
Interface IDs are constructed in the modified EUI-64 format in one of
the following ways:
For all IEEE 802 interface types (for example, Ethernet interfaces
and FDDI interfaces), the first three octets (24 bits) are taken from the
Organizationally Unique Identifier (OUI) of the 48-bit link-layer address (MAC
address) of the interface, the fourth and fifth octets (16 bits) are a fixed
hexadecimal value of FFFE, and the last three octets (24 bits) are taken from
the last three octets of the MAC address. The construction of the interface ID
is completed by setting the Universal/Local (U/L) bit—the seventh bit of the
first octet—to a value of 0 or 1. A value of 0 indicates a locally administered
identifier; a value of 1 indicates a globally unique IPv6 interface identifier.
For tunnel interface types that are used with IPv6 overlay tunnels,
the interface ID is the IPv4 address assigned to the tunnel interface with all
zeros in the high-order 32 bits of the identifier.
Note
For interfaces using Point-to-Point Protocol (PPP), given that the
interfaces at both ends of the connection might have the same MAC address, the
interface identifiers used at both ends of the connection are negotiated
(picked randomly and, if necessary, reconstructed) until both identifiers are
unique. The first MAC address in the router is used to construct the identifier
for interfaces using PPP.
If no IEEE 802 interface types are in the router, link-local IPv6
addresses are generated on the interfaces in the router in the following
sequence:
The router is queried for MAC addresses (from the pool of MAC
addresses in the router).
If no MAC address is available, the serial number of the Route
Processor (RP) or line card (LC) is used to form the link-local address.
Link-Local
Address
A link-local address is an IPv6 unicast address that can be
automatically configured on any interface using the link-local prefix FE80::/10
(1111 1110 10) and the interface identifier in the modified EUI-64 format.
Link-local addresses are used in the neighbor discovery protocol and the
stateless autoconfiguration process. Nodes on a local link can use link-local
addresses to communicate; the nodes do not need site-local or globally unique
addresses to communicate. This figure below shows the structure of a link-local
address.
IPv6 routers must not forward packets that have link-local source or
destination addresses to other links.
IPv4-Compatible IPv6
Address
An IPv4-compatible IPv6 address is an IPv6 unicast address that has
zeros in the high-order 96 bits of the address and an IPv4 address in the
low-order 32 bits of the address. The format of an IPv4-compatible IPv6 address
is 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D. The entire 128-bit IPv4-compatible IPv6
address is used as the IPv6 address of a node and the IPv4 address embedded in
the low-order 32 bits is used as the IPv4 address of the node. IPv4-compatible
IPv6 addresses are assigned to nodes that support both the IPv4 and IPv6
protocol stacks and are used in automatic tunnels. This figure below shows the
structure of an IPv4-compatible IPv6 address and a few acceptable formats for
the address.
Simplified IPv6
Packet Header
The basic IPv4 packet
header has 12 fields with a total size of 20 octets (160 bits). The 12 fields
may be followed by an Options field, which is followed by a data portion that
is usually the transport-layer packet. The variable length of the Options field
adds to the total size of the IPv4 packet header. The shaded fields of the IPv4
packet header are not included in the IPv6 packet header.
The basic IPv6 packet
header has 8 fields with a total size of 40 octets (320 bits). Fields were
removed from the IPv6 header because, in IPv6, fragmentation is not handled by
routers and checksums at the network layer are not used. Instead, fragmentation
in IPv6 is handled by the source of a packet and checksums at the data link
layer and transport layer are used. (In IPv4, the User Datagram Protocol (UDP)
transport layer uses an optional checksum. In IPv6, use of the UDP checksum is
required to check the integrity of the inner packet.) Additionally, the basic
IPv6 packet header and Options field are aligned to 64 bits, which can
facilitate the processing of IPv6 packets.
This table lists the
fields in the basic IPv6 packet header.
Table 2. Basic IPv6 Packet
Header Fields
Field
Description
Version
Similar to the
Version field in the IPv4 packet header, except that the field lists number 6
for IPv6 instead of number 4 for IPv4.
Traffic Class
Similar to the
Type of Service field in the IPv4 packet header. The Traffic Class field tags
packets with a traffic class that is used in differentiated services.
Flow Label
A new field in
the IPv6 packet header. The Flow Label field tags packets with a specific flow
that differentiates the packets at the network layer.
Payload Length
Similar to the
Total Length field in the IPv4 packet header. The Payload Length field
indicates the total length of the data portion of the packet.
Next Header
Similar to the
Protocol field in the IPv4 packet header. The value of the Next Header field
determines the type of information following the basic IPv6 header. The type of
information following the basic IPv6 header can be a transport-layer packet,
for example, a TCP or UDP packet, or an Extension Header.
Hop Limit
Similar to the
Time to Live field in the IPv4 packet header. The value of the Hop Limit field
specifies the maximum number of routers that an IPv6 packet can pass through
before the packet is considered invalid. Each router decrements the value by
one. Because no checksum is in the IPv6 header, the router can decrement the
value without needing to recalculate the checksum, which saves processing
resources.
Source Address
Similar to the
Source Address field in the IPv4 packet header, except that the field contains
a 128-bit source address for IPv6 instead of a 32-bit source address for IPv4.
Destination
Address
Similar to the
Destination Address field in the IPv4 packet header, except that the field
contains a 128-bit destination address for IPv6 instead of a 32-bit destination
address for IPv4.
Following the eight
fields of the basic IPv6 packet header are optional extension headers and the
data portion of the packet. If present, each extension header is aligned to 64
bits. There is no fixed number of extension headers in an IPv6 packet.
Together, the extension headers form a chain of headers. Each extension header
is identified by the Next Header field of the previous header. Typically, the
final extension header has a Next Header field of a transport-layer protocol,
such as TCP or UDP. This figure below shows the IPv6 extension header format.
This table lists the
extension header types and their Next Header field values.
Table 3. IPv6 Extension
Header Types
Header Type
Next Header
Value
Description
Hop-by-hop
options header
0
This header is
processed by all hops in the path of a packet. When present, the hop-by-hop
options header always follows immediately after the basic IPv6 packet header.
Destination
options header
60
The
destination options header can follow any hop-by-hop options header, in which
case the destination options header is processed at the final destination and
also at each visited address specified by a routing header. Alternatively, the
destination options header can follow any Encapsulating Security Payload (ESP)
header, in which case the destination options header is processed only at the
final destination.
Routing header
43
The routing
header is used for source routing.
Fragment
header
44
The fragment
header is used when a source must fragment a packet that is larger than the
maximum transmission unit (MTU) for the path between itself and a destination.
The Fragment header is used in each fragmented packet.
Authentication
header
and
ESP header
51
50
The
Authentication header and the ESP header are used within IP Security Protocol
(IPSec) to provide authentication, integrity, and confidentiality of a packet.
These headers are identical for both IPv4 and IPv6.
Upper-layer
header
6 (TCP)
17 (UDP)
The
upper-layer (transport) headers are the typical headers used inside a packet to
transport the data. The two main transport protocols are TCP and UDP.
Mobility
header
To be done
by IANA
Extension
headers used by mobile nodes, correspondent nodes, and home agents in all
messaging related to the creation and management of bindings.
Path MTU Discovery
for IPv6
As in IPv4, path MTU discovery in IPv6 allows a host to dynamically
discover and adjust to differences in the MTU size of every link along a given
data path. In IPv6, however, fragmentation is handled by the source of a packet
when the path MTU of one link along a given data path is not large enough to
accommodate the size of the packets. Having IPv6 hosts handle packet
fragmentation saves IPv6 router processing resources and helps IPv6 networks
run more efficiently.
In IPv4, the minimum link MTU is 68 octets, which means that the MTU
size of every link along a given data path must support an MTU size of at least
68 octets. In IPv6, the minimum link MTU is 1280 octets. We recommend using an
MTU value of 1500 octets for IPv6 links.
Note
Path MTU discovery is supported only for applications using TCP.
IPv6 Neighbor
Discovery
The IPv6 neighbor discovery (ND) process uses ICMP messages and solicited-node multicast addresses to determine the link-layer
address of a neighbor on the same network (local link), verify the reachability of a neighbor, and keep track of neighboring
routers.
As all incoming control traffic goes through LPTS policer, if the ND packets come in a burst they are policed according to
the configuration. For more details on LPTS, see LPTS Overview.
IPv6 Neighbor
Solicitation Message
A value of 135 in the Type field of the ICMP packet header identifies a
neighbor solicitation message. Neighbor solicitation messages are sent on the
local link when a node wants to determine the link-layer address of another
node on the same local link. When a node wants to determine the link-layer
address of another node, the source address in a neighbor solicitation message
is the IPv6 address of the node sending the neighbor solicitation message. The
destination address in the neighbor solicitation message is the solicited-node
multicast address that corresponds to the IPv6 address of the destination node.
The neighbor solicitation message also includes the link-layer address of the
source node.
After receiving the neighbor solicitation message, the destination node
replies by sending a neighbor advertisement message, which has a value of 136
in the Type field of the ICMP packet header, on the local link. The source
address in the neighbor advertisement message is the IPv6 address of the node
(more specifically, the IPv6 address of the node interface) sending the
neighbor advertisement message. The destination address in the neighbor
advertisement message is the IPv6 address of the node that sent the neighbor
solicitation message. The data portion of the neighbor advertisement message
includes the link-layer address of the node sending the neighbor advertisement
message.
After the source node receives the neighbor advertisement, the source
node and destination node can communicate.
Neighbor solicitation messages are also used to verify the reachability
of a neighbor after the link-layer address of a neighbor is identified. When a
node wants to verifying the reachability of a neighbor, the destination address
in a neighbor solicitation message is the unicast address of the neighbor.
Neighbor advertisement messages are also sent when there is a change in
the link-layer address of a node on a local link. When there is such a change,
the destination address for the neighbor advertisement is the all-nodes
multicast address.
Neighbor solicitation messages are also used to verify the reachability
of a neighbor after the link-layer address of a neighbor is identified.
Neighbor unreachability detection identifies the failure of a neighbor or the
failure of the forward path to the neighbor, and is used for all paths between
hosts and neighboring nodes (hosts or routers). Neighbor unreachability
detection is performed for neighbors to which only unicast packets are being
sent and is not performed for neighbors to which multicast packets are being
sent.
A neighbor is considered reachable when a positive acknowledgment is
returned from the neighbor (indicating that packets previously sent to the
neighbor have been received and processed). A positive acknowledgment—from an
upper-layer protocol (such as TCP)—indicates that a connection is making
forward progress (reaching its destination) or that a neighbor advertisement
message in response to a neighbor solicitation message has been received. If
packets are reaching the peer, they are also reaching the next-hop neighbor of
the source. Therefore, forward progress is also a confirmation that the
next-hop neighbor is reachable.
For destinations that are not on the local link, forward progress
implies that the first-hop router is reachable. When acknowledgments from an
upper-layer protocol are not available, a node probes the neighbor using
unicast neighbor solicitation messages to verify that the forward path is still
working. The return of a solicited neighbor advertisement message from the
neighbor is a positive acknowledgment that the forward path is still working.
(Neighbor advertisement messages that have the solicited flag set to a value of
1 are sent only in response to a neighbor solicitation message.) Unsolicited
messages confirm only the one-way path from the source to the destination node;
solicited neighbor advertisement messages indicate that a path is working in
both directions.
Note
A neighbor advertisement message that has the solicited flag set to a
value of 0 must not be considered as a positive acknowledgment that the forward
path is still working.
Neighbor solicitation messages are also used in the stateless
autoconfiguration process to verify the uniqueness of unicast IPv6 addresses
before the addresses are assigned to an interface. Duplicate address detection
is performed first on a new, link-local IPv6 address before the address is
assigned to an interface. (The new address remains in a tentative state while
duplicate address detection is performed.) Specifically, a node sends a
neighbor solicitation message with an unspecified source address and a
tentative link-local address in the body of the message. If another node is
already using that address, the node returns a neighbor advertisement message
that contains the tentative link-local address. If another node is
simultaneously verifying the uniqueness of the same address, that node also
returns a neighbor solicitation message. If no neighbor advertisement messages
are received in response to the neighbor solicitation message and no neighbor
solicitation messages are received from other nodes that are attempting to
verify the same tentative address, the node that sent the original neighbor
solicitation message considers the tentative link-local address to be unique
and assigns the address to the interface.
Every IPv6 unicast address (global or link-local) must be checked for
uniqueness on the link; however, until the uniqueness of the link-local address
is verified, duplicate address detection is not performed on any other IPv6
addresses associated with the link-local address. The Cisco implementation of
duplicate address detection in the Cisco IOS XR software does not check the
uniqueness of anycast or global addresses that are generated from 64-bit
interface identifiers.
IPv6 Router
Advertisement Message
Router advertisement (RA) messages, which have a value of 134 in the
Type field of the ICMP packet header, are periodically sent out each configured
interface of an IPv6 router. The router advertisement messages are sent to the
all-nodes multicast address.
Router advertisement messages typically include the following
information:
One or more onlink IPv6 prefixes that nodes on the local link can
use to automatically configure their IPv6 addresses
Lifetime information for each prefix included in the advertisement
Sets of flags that indicate the type of autoconfiguration (stateless
or statefull) that can be completed
Default router information (whether the router sending the
advertisement should be used as a default router and, if so, the amount of
time, in seconds, that the router should be used as a default router)
Additional information for hosts, such as the hop limit and MTU a
host should use in packets that it originates
Router advertisements are also sent in response to router solicitation
messages. Router solicitation messages, which have a value of 133 in the Type
field of the ICMP packet header, are sent by hosts at system startup so that
the host can immediately autoconfigure without needing to wait for the next
scheduled router advertisement message. Given that router solicitation messages
are usually sent by hosts at system startup (the host does not have a
configured unicast address), the source address in router solicitation messages
is usually the unspecified IPv6 address (0:0:0:0:0:0:0:0). If the host has a
configured unicast address, the unicast address of the interface sending the
router solicitation message is used as the source address in the message. The
destination address in router solicitation messages is the all-routers
multicast address with a scope of the link. When a router advertisement is sent
in response to a router solicitation, the destination address in the router
advertisement message is the unicast address of the source of the router
solicitation message.
The following router advertisement message parameters can be configured:
The time interval between periodic router advertisement messages
The “router lifetime” value, which indicates the usefulness of a
router as the default router (for use by all nodes on a given link)
The network prefixes in use on a given link
The time interval between neighbor solicitation message
retransmissions (on a given link)
The amount of time a node considers a neighbor reachable (for use by
all nodes on a given link)
The configured parameters are specific to an interface. The sending of
router advertisement messages (with default values) is automatically enabled on
Ethernet and FDDI interfaces. For other interface types, the sending of router
advertisement messages must be manually configured by using the
no ipv6 nd suppress-ra command in interface configuration mode. The sending of router
advertisement messages can be disabled on individual interfaces by using the
ipv6 nd suppress-ra command in interface configuration mode.
Note
For stateless autoconfiguration to work properly, the advertised
prefix length in router advertisement messages must always be 64 bits.
IPv6 Neighbor
Redirect Message
A value of 137 in the Type field of the ICMP packet header identifies an
IPv6 neighbor redirect message. Routers send neighbor redirect messages to
inform hosts of better first-hop nodes on the path to a destination.
Note
A router must be able to determine the link-local address for each of
its neighboring routers to ensure that the target address (the final
destination) in a redirect message identifies the neighbor router by its
link-local address. For static routing, the address of the next-hop router
should be specified using the link-local address of the router; for dynamic
routing, all IPv6 routing protocols must exchange the link-local addresses of
neighboring routers.
After forwarding a packet, a router should send a redirect message to
the source of the packet under the following circumstances:
The destination address of the packet is not a multicast address.
The packet was not addressed to the router.
The packet is about to be sent out the interface on which it was
received.
The router determines that a better first-hop node for the packet
resides on the same link as the source of the packet.
The source address of the packet is a global IPv6 address of a
neighbor on the same link, or a link-local address.
Use the
ipv6 icmp error-interval global configuration
command to limit the rate at which the router generates all IPv6 ICMP error
messages, including neighbor redirect messages, which ultimately reduces
link-layer congestion.
Note
A router must not update its routing tables after receiving a neighbor
redirect message, and hosts must not originate neighbor redirect messages.
Address Repository
Manager
IPv4 and IPv6 Address Repository Manager (IPARM) enforces the uniqueness
of global IP addresses configured in the system, and provides global IP address
information dissemination to processes on route processors (RPs) and line cards
(LCs) using the IP address consumer application program interfaces (APIs),
which includes unnumbered interface information.
Address Conflict
Resolution
There are two parts to conflict
resolution; the conflict database and the conflict set definition.
Conflict
Database
IPARM maintains a global conflict database. IP addresses that conflict
with each other are maintained in lists called conflict sets. These conflict
sets make up the global conflict database.
A set of IP addresses are said to be part of a conflict set if at least
one prefix in the set conflicts with every other IP address belonging to the
same set. For example, the following four addresses are part of a single
conflict set.
address 1: 10.1.1.1/16
address 2: 10.2.1.1/16
address 3: 10.3.1.1/16
address 4: 10.4.1.1/8
When a conflicting IP address is added to a conflict set, an algorithm
runs through the set to determine the highest precedence address within the
set.
This conflict policy algorithm is deterministic, that is, the user can
tell which addresses on the interface are enabled or disabled. The address on
the interface that is enabled is declared as the highest precedence ip address
for that conflict set.
The conflict policy algorithm determines the highest precedence ip
address within the set.