Use of Outgoing Filter Lists in MSDP
By default, an MSDP-enabled device forwards all SA messages it receives to all of its MSDP peers. However,
you can prevent SA messages from being forwarded to MSDP peers by creating outgoing filter lists. Outgoing
filter lists apply to all SA messages, whether locally originated or received from another MSDP peer, whereas
SA origination filters apply only to locally originated SA messages. For more information about enabling a
filter for MSDP SA messages originated by the local device, see the
Controlling SA Messages Originated by
an RP for Local Sources, on page 195
section.
By creating an outgoing filter list, you can control the SA messages that a device forwards to a peer as follows:
•
You can filter all outgoing SA messages forwarded to a specified MSDP peer by configuring the device
to stop forwarding its SA messages to the MSDP peer.
•
You can filter a subset of outgoing SA messages forwarded to a specified MSDP peer based on (S, G)
pairs defined in an extended access list by configuring the device to only forward SA messages to the
MSDP peer that match the (S, G) pairs permitted in an extended access list. The forwarding of all other
SA messages to the MSDP peer will be stopped.
•
You can filter a subset of outgoing SA messages forwarded to a specified MSDP peer based on match
criteria defined in a route map by configuring the device to only forward SA messages that match the
criteria defined in the route map. The forwarding of all other SA messages to the MSDP peer will be
stopped.
•
You can filter a subset of outgoing SA messages from a specified peer based on the announcing RP
address contained in the SA message by configuring the device to filter outgoing SA messages based
on their origin, even after an SA message has been transmitted across one or more MSDP peers. The
forwarding of all other SA messages to the MSDP peer will be stopped.
•
You can configure an outgoing filter list that includes an extended access list, a route map, and either
an RP access list or an RP route map. In this case, all conditions must be true for the MSDP peer to
forward the outgoing SA message.
Arbitrary filtering of SA messages can result in downstream MSDP peers being starved of SA messages
for legitimate active sources. Care, therefore, should be taken when using these sorts of filters. Normally,
outgoing filter lists are used only to reject undesirable sources, such as sources using private addresses.
Caution
Use of Incoming Filter Lists in MSDP
By default, an MSDP-enabled device receives all SA messages sent to it from its MSDP peers. However, you
can control the source information that a device receives from its MSDP peers by creating incoming filter
lists.
By creating incoming filter lists, you can control the incoming SA messages that a device receives from its
peers as follows:
•
You can filter all incoming SA messages from a specified MSDP peer by configuring the device to
ignore all SA messages sent to it from the specified MSDP peer.
•
You can filter a subset of incoming SA messages from a specified peer based on (S, G) pairs defined in
an extended access list by configuring the device to only receive SA messages from the MSDP peer that
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
182
OL-29890-01
Configuring MSDP
Use of Outgoing Filter Lists in MSDP
