Default MSDP Peers
A stub autonomous system also might want to have MSDP peerings with more than one RP for the sake of
redundancy. For example, SA messages cannot just be accepted from multiple default peers, because there is
no RPF check mechanism. Instead, SA messages are accepted from only one peer. If that peer fails, SA
messages are then accepted from the other peer. The underlying assumption here, of course, is that both default
peers are sending the same SA messages.
The figure illustrates a scenario where default MSDP peers might be used. In the figure, a customer that owns
Device B is connected to the Internet through two Internet service providers (ISPs), one that owns Device A
and the other that owns Device C. They are not running BGP or MBGP between them. In order for the customer
to learn about sources in the ISP domain or in other domains, Device B identifies Device A as its default
MSDP peer. Device B advertises SA messages to both Device A and Device C, but accepts SA messages
either from Device A only or Device C only. If Device A is the first default peer in the configuration, it will
be used if it is up and running. Only if Device A is not running will Device B accept SA messages from Device
C.
The ISP will also likely use a prefix list to define which prefixes it will accept from the customer device. The
customer will define multiple default peers, each having one or more prefixes associated with it.
The customer has two ISPs to use. The customer defines both ISPs as default peers. As long as the first default
peer identified in the configuration is up and running, it will be the default peer and the customer will accept
all SA messages it receives from that peer.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
OL-32598-01 205
Configuring MSDP
Default MSDP Peers
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