RIPng Overview

So, the eggheads of the networking industry couldn't bear an IP protocol without RIP and so we get RIPng for our IPv6 networks. The "ng" stands for Next Generation, but it is sometimes referred to as RIPv6 or IPv6 RIP.

Below are listed some of the facts of RIPng. The below summary is based on the defaults of Cisco's implementation of RIPng and there are only few differences compared to RIPv2 for IPv4.

• Defined in RFC 2080
• Runs on port UDP/521 (not 520 to avoid clashing with IPv4 RIP configurations)
• Sends updates to multicast address FF02::9
• Metric is still based on hop count with 15 being the maximum and 16 being infinity (unreachable)
• Unlike RIPv2, the sending router does not increment the hop count in advertised routes before sending it out to its neighbors. Instead, it does the most logical thing and advertises what it has in its routing table. The receiving router is responsible for incrementing the entries before entering it into its own routing table
• Default administrative distance is 120
• It is driven mainly by timers
• Update timer: 30 sec.
• sends out the entire routing table every 30 sec. on RIP enabled interfaces (routes affected by the split horizon rule are excluded from the update)
• Triggered updates occur when a route change occurs and an update, including only the changed route, is sent out. Regular updates are unaffected by this and are still sent per the update timer interval
• Cisco uses a jitter variable to avoid update synchronization, just like in RIPv2, but I am unclear on the specific details - I can only assume they function the same way.
• Expiration timer: 180 sec.
• Similar to RIPv2 invalid timer. The expiration timer tracks the validity of a specific route. It resets to 0 whenever a route is received in an update and a route is considered invalid if the route is not received within 180 seconds.
• After the expiration timer expires the route is advertised with a metric of 16 (unreachable) until it is purged from the routing table
• Holddown timer: 0 sec.
• Cisco defaults to not using the holddown timer in RIPng
• Garbage collection timer: 120 sec.
• Unlike RIPv1 and v2, RIPng garbage collection timer starts counting after the specific routes expiration timer is exceeded
• The route is advertised with a metric of 16 (unreachable) for 120 seconds - after which the route is purged from the routing table
• An update message can contain as many entries as the MTU size allows (unlike RIPv1 and v2, which only allows for 25 entries per update message)
• Does not natively support authentication
• It uses IPv6 built-in authentication features (I will find the time to do a post on that on a later date)
• The ring is able to tag routes being redistributed into the routing process
• Unlike RIPv1 and v2, RIPng supports multiple instances running on the same router
• Cisco uses named instances, where instance names are locally significant and do not have to match between routers
• Use the global configuration command ipv6 router rip <instance name> to enter the general process configuration mode
• Use the interface sub-command ipv6 rip <instance name> enable to enable RIPng on a specific interface

Below is a packet capture of a RIPng update message (also known as a response) sent from the IPv6 link-local address of FE80::13:3 to the IPv6 multicast address of FF02::9.

RIPng response message, including two prefixes