Narbik/IPExpert RIPv2 Notes

General Notes

• passive-interface default is recommended, due to the network statement being classful
• don’t forget to consider switch-based solutions like vlan access-maps and port access-lists (blocking udp/520) to prevent updates from propagating between routers if the task restricts your configuration options on the routers themselves.
• CCIE Links page updated with RIPv2 links

Timers

• default basic timers are 30/120/120/240 (update, invalid, hold down, flush)
• periodic updates can be delayed after a triggered update with the sleep parameter at the end of the timers basic router command.
• the “hold down” timer is Cisco-proprietary. Set it to 0 if you need to retain full compatibility with RFC 2453.

Distribute Lists

• distribute-list uses a separate ip prefix-list for defining the gateway and the routes

Default Originate

• the route-map option to default-information originate causes the 0/0 route to only be injected into RIP if the route-map is satisfied (e.g. if a route exists)

Multicast / Broadcast / Unicast

• RIPv2 defaults to sending updates via multicast (224.0.0.9)
• The passive-interface and neighbor router commands change it to unicast
• The ip rip v2-broadcast interface command changes it to broadcast
• A very tricky way to force unicast updates without using the neighbor command:

  ip nat outside udp X.X.X.X 520 224.0.0.9 520

  int se0/0/0

    ip nat outside

  This converts the inbound multicast updates to unicast, which will create a NAT table entry and translate all outbound RIP updates to unicast as well (NAT is bidirectional)

Authentication

• IOS 12.4 supposedly requires a valid send-lifetime configured for a key before it will work.
• RIP will always use the first valid key when sending updates out an interface.

Route Filtering

• The three methods to kill a route:
  • distribute-list with an ACL
  • offset-list pushing the metric beyond 16
  • distance command setting the AD to 255