Cisco Catalyst 3850 series Configuration Manual page 261

Configuring MSDP
Although the following illustration and example uses routers in the configuration, any device (router or
Note
switch) can be used.
Figure 12: Default MSDP Peer Scenario
Device B advertises SAs to Device A and Device C, but uses only Device A or Device C to accept SA messages.
If Device A is first in the configuration file, it will be used if it is up and running. Only when Device A is not
running will Device B accept SAs from Device C. This is the behavior without a prefix list.
If you specify a prefix list, the peer will be 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 device
has connectivity to this peer and the peer is alive. If the first configured peer goes down or the connectivity
to this peer goes down, the second configured peer becomes the active default, and so on.
The following example shows a partial configuration of Device A and Device C in the figure. Each of these
ISPs may have more than one customer using default peering, like the customer in the figure. In that case,
they may have similar configurations. That is, they will only accept SAs from a default peer if the SA is
permitted by the corresponding prefix list.
Device A Configuration
ip msdp default-peer 10.1.1.1
ip msdp default-peer 10.1.1.1 prefix-list site-b ge 32
ip prefix-list site-b permit 10.0.0.0/8
OL-32598-01
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
Example: Configuring a Default MSDP Peer
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