In this software
release, because BGP and MBGP are not supported, you cannot configure an MSDP
peer on the local switch by using the
ip msdp peer
global configuration command. Instead, you define a default MSDP peer (by using
default-peer global configuration command) from which to accept
all SA messages for the switch. The default MSDP peer must be a previously
configured MSDP peer. Configure a default MSDP peer when the switch is not BGP-
or MBGP-peering with an MSDP peer. If a single MSDP peer is configured, the
switch always accepts all SA messages from that peer.
This figure shows a
network in which default MSDP peers might be used. A customer who owns Switch B
is connected to the Internet through two Internet service providers (ISPs), one
owning Router A and the other owning Router C. They are not running BGP or MBGP
between them. To learn about sources in the ISP’s domain or in other domains,
Switch B at the customer site identifies Router A as its default MSDP peer.
Switch B advertises SA messages to both Router A and Router C but accepts SA
messages only from Router A or only from Router C. If Router A is first in the
configuration file, it is used if it is running. If Router A is not running,
only then does Switch B accept SA messages from Router C. This is the default
behavior without a prefix list.
If you specify a
prefix list, the peer is a default peer only for the prefixes in the list. You
can have multiple active default peers when you have a prefix list associated
with each. When you do not have any prefix lists, you can configure multiple
default peers, but only the first one is the active default peer as long as the
router has connectivity to this peer and the peer is alive. If the first
configured peer fails or the connectivity to this peer fails, the second
configured peer becomes the active default, and so on.
The ISP probably
uses a prefix list to define which prefixes it accepts from the customer’s