Extreme Networks ExtremeWare XOS 11.3, Manual

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BGP Features
ExtremeWare XOS 11.3 Concepts Guide
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Changes made to the parameters of a peer group are applied to all neighbors in the peer group.
Modifying the following parameters will automatically disable and enable the neighbors before changes
take effect:
●
remote-as
●
timer
●
source-interface
●
soft-in-reset
●
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 <remoteaddr> peer-group <peer-group-name> {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 | <remoteaddr>] peer-group [<peer-group-name> | 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