IPv6 Routing: Route Redistribution

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-routers 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 master 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.

RIP supports the use of a route map to select routes for redistribution. Routes may be specified by prefix, using a route-map prefix list, or by tag, using the route-map "match tag" function.

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.

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]

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

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 IPv6 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 lekeyword. 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	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.

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

In the following example, the IPv6 RIP process named process1 is enabled on the router and on Ethernet interface 0/0. The IPv6 default route (::/0) is advertised in addition to all other routes in router updates sent on Ethernet interface 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 Ethernet interface 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 Ethernet0/0
!
interface Ethernet0/0
 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:
    Ethernet0/0
  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
     Ethernet0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8::/16, metric 2 tag 4, installed
     Ethernet0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8:1::/16, metric 2 tag 4, installed
     Ethernet0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 2001:DB8:2::/16, metric 2 tag 4, installed
     Ethernet0/0/FE80::A8BB:CCFF:FE00:B00, expires in 13 secs
 ::/0, metric 2, installed
     Ethernet0/0/FE80::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/Ethernet0/0 [4 paths]