Netgear XCM8810 Chassis User Manual - Page 714

NETGEAR 8800 User Manual • password Adding Neighbors to a BGP Peer Group To create a new neighbor and add it to a BGP peer group, use the following command: create bgp neighbor peer-group {multi-hop} The new neighbor is created as part of the peer group and inherits all of the existing parameters of the peer group. The peer group must have remote AS configured. To add an existing neighbor to a peer group, use the following command: configure bgp neighbor [all | ] peer-group [ | none] {acquire-all} If you do not specify the acquire-all option, only the mandatory parameters are inherited from the peer group. If you specify the acquire-all option, all of the parameters of the peer group are inherited. This command disables the neighbor before adding it to the peer group. To remove a neighbor from a peer group, use the peer-group none option. When you remove a neighbor from a peer group, the neighbor retains the parameter settings of the group. The parameter values are not reset to those the neighbor had before it inherited the peer group values. BGP Route Flap Dampening Route flap dampening is a BGP feature designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when it is repeatedly available, then unavailable, then available, then unavailable, and so on. When a route becomes unavailable, a withdrawal message is sent to other connected routers, which in turn propagate the withdrawal message to other routers. As the route becomes available again, an advertisement message is sent and propagated throughout the network. As a route repeatedly changes from available to unavailable, large numbers of messages propagate throughout the network. This is a problem in an internetwork connected to the Internet because a route flap in the Internet backbone usually involves many routes. Minimizing the Route Flap The route flap dampening feature minimizes the flapping problem as follows. Suppose that the route to network 172.25.0.0 flaps. The router (in which route dampening is enabled) assigns network 172.25.0.0 a penalty of 1000 and moves it to a "history" state in which the penalty value is monitored. The router continues to advertise the status of the route to neighbors. The penalties are cumulative. When the route flaps so often that the penalty exceeds a configurable suppress limit, the router stops advertising the route to network 172.25.0.0, regardless of how many times it flaps. Thus, the route is dampened. 714 | Chapter 26. BGP