IPv6 Routing: Route Redistribution

IPv6 route redistribution allows routes to be specified by prefix, using a route-map prefix list, or by tag, using the route-map "match tag" function.

Information About IPv6 Route Redistribution

RIP for IPv6

IPv6 RIP functions the same and offers the same benefits as RIP in IPv4. RIP enhancements for IPv6, detailed in RFC 2080, include support for IPv6 addresses and prefixes, and the use of the all-RIP-devices multicast group address FF02::9 as the destination address for RIP update messages.

In the Cisco software implementation of IPv6 RIP, each IPv6 RIP process maintains a local routing table, referred to as a Routing Information Database (RIB). The IPv6 RIP RIB contains a set of best-cost IPv6 RIP routes learned from all its neighboring networking devices. If IPv6 RIP learns the same route from two different neighbors, but with different costs, it will store only the lowest cost route in the local RIB. The RIB also stores any expired routes that the RIP process is advertising to its neighbors running RIP. IPv6 RIP will try to insert every non-expired route from its local RIB into the primary IPv6 RIB. If the same route has been learned from a different routing protocol with a better administrative distance than IPv6 RIP, the RIP route will not be added to the IPv6 RIB but the RIP route will still exist in the IPv6 RIP RIB.

How to Configure IPv6 Route Redistribution

Redistributing Routes into an IPv6 RIP Routing Process

The maximum metric that RIP can advertise is 16, and a metric of 16 denotes a route that is unreachable. Therefore, if you are redistributing routes with metrics greater than or equal to 16, then by default RIP will advertise them as unreachable. These routes will not be used by neighboring routers. The user must configure a redistribution metric of less than 15 for these routes.


Note

You must to advertise a route with metric of 15 or less. A RIP router always adds an interface cost--the default is 1--onto the metric of a received route. If you advertise a route with metric 15, your neighbor will add 1 to it, making a metric of 16. Because a metric of 16 is unreachable, your neighbor will not install the route in the routing table.

If no metric is specified, then the current metric of the route is used. To find the current metric of the route, enter the show ipv6 route command.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ipv6 rip word enable
  5. redistribute protocol [process-id ] {level-1 | level-1-2 | level-2 } [metric metric-value ] [metric-type {internal | external }] [route-map map-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

interface type number

Example:


Router(config)# interface gigabitethernet 0/0/0

Specifies the interface type and number, and enters interface configuration mode.

Step 4

ipv6 rip word enable

Example:


Router(config-if)# ipv6 router one enable

Enables an IPv6 Routing Information Protocol (RIP) routing process on an interface.

Step 5

redistribute protocol [process-id ] {level-1 | level-1-2 | level-2 } [metric metric-value ] [metric-type {internal | external }] [route-map map-name ]

Example:


Router(config-router)# redistribute bgp 65001 route-map bgp-to-rip

Redistributes the specified routes into the IPv6 RIP routing process.

  • The protocol argument can be one of the following keywords: bgp , connected , isis , rip , or static .

  • The rip keyword and process-id argument specify an IPv6 RIP routing process.

Note

 

The connected keyword refers to routes that are established automatically by assigning IPv6 addresses to an interface.

Configuring Route Tags for IPv6 RIP Routes

When performing route redistribution, you can associate a numeric tag with a route. The tag is advertised with the route by RIP and will be installed along with the route in neighboring router’s routing table.

If you redistribute a tagged route (for example, a route in the IPv6 routing table that already has a tag) into RIP, then RIP will automatically advertise the tag with the route. If you use a redistribution route map to specify a tag, then RIP will use the route map tag in preference to the routing table tag.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. route-map map-tag [permit | deny ] [sequence-number ]
  4. match ipv6 address {prefix-list prefix-list-name | access-list-name
  5. set tag tag-value

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

route-map map-tag [permit | deny ] [sequence-number ]

Example:


Router(config)# route-map bgp-to-rip permit 10

Defines a route map, and enters route-map configuration mode.

  • Follow this step with a match command.

Step 4

match ipv6 address {prefix-list prefix-list-name | access-list-name

Example:


Router(config-route-map)# match ipv6 address prefix-list bgp-to-rip-flt

Specifies a list of IPv6 prefixes to be matched.

Step 5

set tag tag-value

Example:


Router(config-route-map)# set tag 4

Sets the tag value to associate with the redistributed routes.

Filtering IPv6 RIP Routing Updates

Route filtering using distribute lists provides control over the routes RIP receives and advertises. This control may be exercised globally or per interface.

Filtering is controlled by distribute lists. Input distribute lists control route reception, and input filtering is applied to advertisements received from neighbors. Only those routes that pass input filtering will be inserted in the RIP local routing table and become candidates for insertion into the IPv6 routing table.

Output distribute lists control route advertisement; Output filtering is applied to route advertisements sent to neighbors. Only those routes passing output filtering will be advertised.

Global distribute lists (which are distribute lists that do not apply to a specified interface) apply to all interfaces. If a distribute list specifies an interface, then that distribute list applies only to that interface.

An interface distribute list always takes precedence. For example, for a route received at an interface, with the interface filter set to deny, and the global filter set to permit, the route is blocked, the interface filter is passed, the global filter is blocked, and the route is passed.

IPv6 prefix lists are used to specify certain prefixes or a range of prefixes that must be matched before a permit or deny statement can be applied. Two operand keywords can be used to designate a range of prefix lengths to be matched. A prefix length of less than, or equal to, a value is configured with the le keyword. A prefix length greater than, or equal to, a value is specified using the ge keyword. The ge and le keywords can be used to specify the range of the prefix length to be matched in more detail than the usual ipv6-prefix / prefix-length argument. For a candidate prefix to match against a prefix list entry three conditions can exist:

  • The candidate prefix must match the specified prefix list and prefix length entry.

  • The value of the optional le keyword specifies the range of allowed prefix lengths from the prefix-length argument up to, and including, the value of the le keyword.

  • The value of the optional ge keyword specifies the range of allowed prefix lengths from the value of the ge keyword up to, and including, 128.


Note

Note that the first condition must match before the other conditions take effect.

An exact match is assumed when the ge or le keywords are not specified. If only one keyword operand is specified then the condition for that keyword is applied, and the other condition is not applied. The prefix-length value must be less than the ge value. The ge value must be less than, or equal to, the le value. The le value must be less than or equal to 128.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ipv6 prefix list prefix-list-name seq seq-number ] {deny ipv6-prefix /prefix-length | description text } [ge ge-value ] [le le-value
  4. ipv6 prefix list prefix-list-name seq seq-number ] {deny ipv6-prefix /prefix-length | description text } [ge ge-value ] [le le-value
  5. Repeat Steps 3 and 4 as many times as necessary to build the prefix list.
  6. ipv6 router rip name
  7. distribute-list prefix-list prefix-list-name in | out } [interface-type interface-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

ipv6 prefix list prefix-list-name seq seq-number ] {deny ipv6-prefix /prefix-length | description text } [ge ge-value ] [le le-value

Example:


Router(config)# ipv6 prefix-list abc permit 2001:DB8::/16

Creates an entry in the IPv6 prefix list.

Step 4

ipv6 prefix list prefix-list-name seq seq-number ] {deny ipv6-prefix /prefix-length | description text } [ge ge-value ] [le le-value

Example:


Router(config)# ipv6 prefix-list abc deny ::/0

Creates an entry in the IPv6 prefix list.

Step 5

Repeat Steps 3 and 4 as many times as necessary to build the prefix list.

--

Step 6

ipv6 router rip name

Example:


Router(config)# ipv6 router rip process1

Configures an IPv6 RIP routing process.

Step 7

distribute-list prefix-list prefix-list-name in | out } [interface-type interface-number

Example:


Router(config-rtr-rip)# distribute-list prefix-list process1 in gigabitethernet 0/0/0

Applies a prefix list to IPv6 RIP routing updates that are received or sent on an interface.

Configuration Examples for IPv6 Route Redistribution

Example: Enabling the RIP for IPv6 Process

In the following example, the IPv6 RIP process named process1 is enabled on the router and on Gigabit Ethernet interface 0/0/0. The IPv6 default route (::/0) is advertised in addition to all other routes in router updates sent on Gigabit Ethernet interface 0/0/0. Additionally, BGP routes are redistributed into the RIP process named process1 according to a route map where routes that match a prefix list are also tagged. The number of parallel paths is set to one to allow the route tagging, and the IPv6 RIP timers are adjusted. A prefix list named eth0/0-in-flt filters inbound routing updates on Gigabit Ethernet interface 0/0/0. 

ipv6 router rip process1
 maximum-paths 1
 redistribute bgp 65001 route-map bgp-to-rip
 distribute-list prefix-list eth0/0-in-flt in Gigabitethernet0/0/0
!
interface Gigabitethernet0/0/0
 ipv6 address 2001:DB8::/64 eui-64
 ipv6 rip process1 enable
 ipv6 rip process1 default-information originate
!
ipv6 prefix-list bgp-to-rip-flt seq 10 deny 2001:DB8:3::/16 le 128
ipv6 prefix-list bgp-to-rip-flt seq 20 permit 2001:DB8:1::/8 le 128
!
ipv6 prefix-list eth0/0-in-flt seq 10 deny ::/0
ipv6 prefix-list eth0/0-in-flt seq 15 permit ::/0 le 128
!
route-map bgp-to-rip permit 10
 match ipv6 address prefix-list bgp-to-rip-flt
 set tag 4

In the following example, output information about all current IPv6 RIP processes is displayed using the show ipv6 rip command: 

Device> show ipv6 rip

RIP process "process1", port 521, multicast-group FF02::9, pid 62
     Administrative distance is 120. Maximum paths is 1
     Updates every 5 seconds, expire after 15
     Holddown lasts 10 seconds, garbage collect after 30
     Split horizon is on; poison reverse is off
     Default routes are generated
     Periodic updates 223, trigger updates 1
  Interfaces:
    Gigabitethernet0/0/0
  Redistribution:
    Redistributing protocol bgp 65001 route-map bgp-to-rip

In the following example, output information about a specified IPv6 RIP process database is displayed using the show ipv6 rip command with the name argument and the database keyword. In the following output for the IPv6 RIP process named process1, timer information is displayed, and route 2001:DB8::16/64 has a route tag set: 

Device> show ipv6 rip process1 database

RIP process "process1", local RIB
 2001:DB8::/64, metric 2
     Gigabitethernet0/0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8::/16, metric 2 tag 4, installed
     Gigabitethernet0/0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8:1::/16, metric 2 tag 4, installed
     Gigabitethernet0/0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8:2::/16, metric 2 tag 4, installed
     Gigabitethernet0/0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 ::/0, metric 2, installed
     Gigabitethernet0/0/0FE80::A8BB:CCFF:FE00:B00, expires in 13 secs

In the following example, output information for a specified IPv6 RIP process is displayed using the show ipv6 rip command with the name argument and the next-hops keyword: 

Device> show ipv6 rip process1 next-hops

RIP process "process1", Next Hops
  FE80::A8BB:CCFF:FE00:A00/Gigabitethernet0/0/0 [4 paths]

Additional References

Related Documents

Related Topic

Document Title

IPv6 addressing and connectivity

IPv6 Configuration Guide

IPv6 commands

Cisco IOS IPv6 Command Reference

Cisco IOS IPv6 features

Cisco IOS IPv6 Feature Mapping

Standards and RFCs

Standard/RFC

Title

RFCs for IPv6

IPv6 RFCs

MIBs

MIB

MIBs Link

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for IPv6 Routing: Route Redistribution

Table 1. Feature Information for IPv6 Routing: Route Redistribution

Feature Name

Releases

Feature Information

IPv6 Routing: Route Redistribution

Cisco IOS XE Release 2.1

Routes may be specified by prefix, using a route-map prefix list, or by tag, using the route-map “match tag” function.

The following commands were introduced or modified: distribute-list prefix-list , ipv6 prefix list , ipv6 rip enable , ipv6 router rip , match ipv6 address , redistribute , route-map , set tag , show ipv6 rip .