A robust network can withstand outages and keep applications running smoothly. Router redundancy on LAN segments is required to maintain communication in the event of a router failure. Hosts on the IPv4 LAN, however, are very likely to rely on a single default router to communicate to hosts on a remote segment. If the default router fails, the host is not informed, and therefore sends traffic to a black hole. Router redundancy protocols, such as the Virtual Router Redundancy..
As noted in Figure 10-1, if a DR is elected, the election occurs after the routers have become neighbors, but before they send DD packets and reach the ExStart neighbor state. When an OSPF router reaches the 2-way state with the first neighbor on an interface, it has already received at least one Hello from that neighbor. If the Hello messages state a DR of 0.0.0.0—meaning none has been elected—the router waits before attempting to elect a DR. This typically occurs after ..
All the options for IP forwarding (routing) in this chapter had one thing in common: The destination IP address in the packet header was the only thing in the packet that was used to determine how the packet was forwarded. Policy routing allows a router to make routing decisions based on information besides the destination IP address. Policy routing’s logic begins with the ip policy command on an interface. This command tells IOS to process incoming packets with different l..
GP/MPLS Graceful Restart Operation
This section describes the operation of the BGP with an MPLS graceful restart mechanism using the network shown in Figure 7-11. The following discussion assumes that LSR1 and LSR2 are capable of both BGP with MPLS graceful restart and NSF. The following sequence of steps does not necessarily indicate the processing steps of a specific implementation. This description is intended to provide a functional view. • During BGP session establishment, LSR1 and LS..
Setting the Router As the NTP Master for the Network
There is no need for a dedicated NTP server; you can pick one or two routers to act as authoritative NTP servers for the whole network. (The router should have a calendar function): Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#clock timezone EST 5 Router(config)#clock summer-time EDT recurring Router(config)#clock calendar-valid Router(config)#ntp master 8 Router(config)#end Router# When no authoritative time s..
