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RIP Timers The Cisco implementation of RIP uses four timers: Update Invalid Flush Holddown RIP sends its full routing table out all configured interfaces. The table is sent periodically as a broadcast (255.255.255.255) for Ver.1 and multicast (224.0.0.9) for Ver.2 to all hosts. Update Timer The update timer specifies the frequency of the periodic broadcasts. By default, the update timer is set to 30 seconds. Each route has a timeout value associated with it. The timeout gets reset every time the router receives a routing update containing the route. Invalid Timer When the timeout value expires, the route is marked as unreachable because it is marked invalid. The router marks the route invalid by setting the metric to 16. The route is retained in the routing table. By default, the invalid timer is 180 seconds, or six updates periods (30 x 6 = 180). Flush Timer A route entry marked as invalid is retained in the routing table until the flush timer expires. By default, the flush timer is 2

Where IPv4 has ARP, IPv6 has NDP, the neighbour discovery protocol. For simple purposes, NDP and ARP are very similar: one node sends out a request packet (called a neighbour solicitation in NDP), and the node it was looking for sends back a reply (neighbour advertisement) giving its link-layer address. NDP is part of ICMPv6, unlike ARP, which doesn't even run over IP. NDP also uses multicast rather than broadcast packets, and that deserves a little more explanation. For each unicast address it responds to, each host listens on a solicited-node multicast address. The solicited-node multicast address for a given unicast address is constructed by taking the last three octets of the unicast address and prepending FF02::1:FF00:0000/104. Thus, the solicited-node multicast address of 2001:630:200:8100:02C0:4FFF:FE68:12CB is FF02::1:FF68:12CB. It's the solicited-node multicast address that a node uses as the destination of a neighbour solicitation packet. This use of multicast means t