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Table Of Contents
Multicast Source Discovery Protocol
Supported Standards, MIBs, and RFCs
Requesting Source Information from an MSDP Peer
Controlling Source Information Your Router Originates
Filtering Source-Active Request Messages
Controlling Source Information Your Router Forwards
Using TTL to Limit the Multicast Data Sent in SA Messages
Controlling Source Information Your Router Receives
Configuring a Default MSDP Peer
Configuring an MSDP Mesh Group
Including a Bordering PIM Dense-Mode Region in MSDP
Configuring an Originating Address Other Than the RP Address
Monitoring and Maintaining MSDP
Multicast Source Discovery Protocol
This feature module describes the Multicast Source Discovery Protocol feature. It includes information on the benefits of the new feature, supported platforms, related documents, and so forth.
This document includes the following sections:
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Supported Standards, MIBs, and RFCs
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Feature Overview
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparse-mode (SM) domains. MSDP allows multicast sources for a group to be known to all rendezvous point(s) (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains. An RP runs MSDP over TCP to discover multicast sources in other domains.
An RP in a PIM-SM domain has an MSDP peering relationship with MSDP-enabled routers in another domain. The peering relationship occurs over a TCP connection, where primarily a list of sources sending to multicast groups is exchanged. The TCP connections between RPs are achieved by the underlying routing system. The receiving RP uses the source lists to establish a source path.
The purpose of this topology is to have domains discover multicast sources in other domains. If the multicast sources are of interest to a domain that has receivers, multicast data is delivered over the normal, source-tree building mechanism in PIM-SM.
MSDP is also used to announce sources sending to a group. These announcements must originate at the domain's RP.
MSDP depends heavily on (M)BGP for interdomain operation. It is recommended that you run MSDP in RPs in your domain that are RPs for sources sending to global groups to be announced to the internet.
How MSDP Works
illustrates MSDP operating between two MSDP peers. PIM uses MSDP as the standard mechanism to register a source with the RP of a domain.
When MSDP is configured, the following sequence occurs. When a source's first data packet is registered by the first-hop router, that same data packet is decapsulated by the RP and forwarded down the shared tree. That packet is also re-encapsulated in a Source-Active (SA) message that is immediately forwarded to all MSDP peers. The SA message identifies the source, the group the source is sending to, and the RP's own address or the originator ID, if configured. If the peer is an RP and has a member of that multicast group, the data packet is decapsulated and forwarded down the shared-tree in the remote domain.
The PIM designated router (DR) directly connected to the source sends the data encapsulated in a PIM Register message to the RP in the domain.
Note
Each MSDP peer receives and forwards the SA message away from the originating RP to achieve "peer-RPF flooding." The concept of peer-RPF flooding is with respect to forwarding SA messages. The router examines the BGP or MBGP routing table to determine which peer is the next hop toward the originating RP of the SA message. Such a peer is called an "RPF peer" (Reverse-Path Forwarding peer). The router forwards the message to all MSDP peers other than the RPF peer.
If the MSDP peer receives the same SA message from a non-RPF peer toward the originating RP, it drops the message. Otherwise, it forwards the message on to all its MSDP peers.
When an RP for a domain receives an SA message from an MSDP peer, it determines if it has any group members interested in the group the SA message describes. If the (*,G) entry exists with a nonempty outgoing interface list, the domain is interested in the group, and the RP triggers an (S,G) join toward the source.
Figure 1 MSDP Running Between RP Peers
Benefits
MSDP has the following benefits:
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Supported Platforms
MSDP operates on all Cisco IOS platforms that run Cisco IOS Release 11.1 CC, 12.0(5)S, or 12.0(7)T.
Prerequisites
Before configuring MSDP, the addresses of all MSDP peers must be known in BGP or MBGP. If that does not occur, you must configure MSDP default peering when you configure MSDP.
Supported Standards, MIBs, and RFCs
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
None
Standards
This feature supports Internet Engineering Task Force draft Multicast Source Discovery Protocol (MSDP).
Configuration Tasks
To configure an MSDP peer and various MSDP options, perform the following tasks. The first task is required; the remaining are optional.
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Configuring an MSDP Peer
You enable MSDP by configuring an MSDP peer to the local router.
Note
To configure an MSDP peer, use the following commands in global configuration mode. The second command is optional.
Caching Source-Active State
By default, the router does not cache source/group pairs from received SA messages. Once the router forwards the MSDP Source-Active information, it does not store it in memory. Therefore, if a member joins a group soon after a Source-Active message is received by the local RP, that member will have to wait until the next SA message to hear about the source. This delay is known as join latency.
If you want to sacrifice some memory in exchange for reducing the latency of the source information, you can configure the router to cache Source-Active messages. To have the router cache source/group pairs, use the following command in global configuration mode
ip msdp cache-sa-state [list access-list-number]
Creates SA state (cache source/group pairs). Those pairs that pass the access list are cached.
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An alternative to caching the source-active state is to request source information from a peer, which is described in the section "Requesting Source Information from an MSDP Peer." If you cache the information, you don't need to trigger a request for it.
Requesting Source Information from an MSDP Peer
Local RPs can send Source-Active Requests and get immediate response for all active sources for a given group. By default, the router does not send any Source-Active Request messages to its MSDP peers when a new member joins a group and wants to receive multicast traffic. The new member just waits to receive the next periodic Source-Active message.
If you want a new member of a group to learn the current, active multicast sources in a connected PIM sparse-mode domain that are sending to a group, configure the router to send Source-Active Request messages to the specified MSDP peer when a new member joins a group. Doing so reduces join latency, but requires some memory.
Note that information can be requested only from caching peers.
To configure this feature, use the following command in global configuration mode
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Repeat the preceding command for each MSDP peer that you want to supply you with Source-Active messages.
An alternative to requesting source information is to cache the source-active state, which is described in the earlier section "Caching Source-Active State." If you cache the information, you don't need to trigger a request for it.
Controlling Source Information Your Router Originates
There are two ways to control the multicast source information that originates with your router. You can control the following:
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To control which sources you will advertise, see the section "Redistributing Sources" later in this document. To control whom you will provide source information to, see the section "Controlling Source Information Your Router Forwards."
Redistributing Sources
Source-Active messages are originated on RPs to which sources have registered. By default, any source that registers with an RP will be advertised. The "A flag" is set in the RP when a source is registered. This means the source will be advertised in an SA unless it is filtered with the command below.
To further restrict which registered sources are advertised, use the following command in global configuration mode. The access list or autonomous system path access list determines which (S,G) pairs are advertised
ip msdp redistribute [list access-list-name] [asn aspath-access-list-number] [route-map map]
Advertises (S,G) pairs that pass the access list or route map to other domains.
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Note
Filtering Source-Active Request Messages
By default, only routers that are caching Source-Active information can respond to Source-Active Reuqests. By default, such a router honors all Source-Active Request messages from its MSDP peers. That is, it will supply the IP addresses of the sources that are active.
However, you can configure the router to ignore all Source-Active Requests from an MSDP peer. Or, you can honor only those Source-Active Request messages from a peer for groups described by a standard access list. If the access list passes, Source-Active Request messages will be accepted. All other such messages from the peer for other groups will be ignored.
To configure one of these options, use the appropriate command in global configuration mode
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Controlling Source Information Your Router Forwards
By default, the router forwards all Source-Active messages it receives to all of its MSDP peers. However, you can prevent outgoing messages from being forwarded to a peer by using a filter or by setting a time to live (TTL). These methods are described in the following sections.
Using a Filter
By creating a filter, you can do one of the following:
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To apply a filter, use one of the following commands in global configuration mode
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Using TTL to Limit the Multicast Data Sent in SA Messages
You can use TTL to control what data will be encapsulated in the first SA message for every source. For example, you could limit internal traffic to a TTL of 8. If you want other groups to go to external locations, you would have to send those packets with a TTL greater than 8.
To establish a TTL threshold, use the following command in global configuration mode:
ip msdp ttl-threshold {ip-address | name} ttl
Limits which multicast data will be encapsulated in the first Source-Active message to the specified MSDP peer.
Controlling Source Information Your Router Receives
By default, the router receives all Source-Active messages its MSDP Reverse-Path Forwarding peers send to it. However, you can control the source information you receive from MSDP peers by filtering incoming Source-Active messages. In other words, you can configure the router not to accept them.
You can do one of the following:
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To apply a filter, use one of the following commands in global configuration mode
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Configuring a Default MSDP Peer
An MSDP peer of the local router is probably a BGP peer also. However, if you do not want to have or cannot have a BGP peer, you could define a default MSDP peer from which to accept all SA messages. The default MSDP peer must be a previously configured MSDP peer. Perform this task when you are not BGP- or MBGP-peering with an MSDP peer. If a single MSDP peer is configured, a router will always accept all SA messages sent to it from that peer.
illustrates a scenario where default MSDP peers might be used. In the figure, a customer who owns Router B is connected to the internet via two Internet Service Providers (ISPs), one who owns Router A and the other who owns Router C. They are not running BGP or MBGP between them. In order for the customer to learn about sources in the ISP's domain or in other domains, Router B identifies Router A as its default MSDP peer. Router B advertises SA messages to both Router A and Router C, but accepts SA messages either from Router A only or Router C only. If Router A is first in the configuration file, it will be used if it is up and running. If Router A isn't running, then and only then will Router B accept SA messages from Router C.
The ISP will also likely use a prefix list to define which prefixes it will accept from the customer's router. The customer will define multiple default peers, each having one or more prefixes associated with it.
The customer has two ISPs to use. He 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.
Figure 2 Default MSDP Peer Scenario
Router B advertises SAs to Router A and Router C, but uses only Router A or Router C to accept SA messages. If Router A is first in the configuration file, it will be used if it is up and running. If Router A isn't running, then, and only then, will Router B accept SAs from Router 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 router 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.
To specify a default MSDP peer, use the following command in global configuration mode
ip msdp default-peer ip-address | name [prefix-list list]
Defines a default MSDP peer.
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See the section "Default MSDP Peer" for a sample configuration.
Configuring an MSDP Mesh Group
An MSDP mesh group is a group of MSDP speakers that have fully meshed MSDP connectivity between one another. Any SA messages received from a peer in a mesh group are not forwarded to other peers in the same mesh group. Thus, you reduce SA message flooding and simplify peer-RPF flooding. The command below is used when there are multiple RPs within a domain. It is especially used to transit SA messages across a domain.
You can configure multiple mesh groups (with different names) in a single router.
To create a mesh group, use the following command in global configuration mode for each MSDP peer in the group:
ip msdp mesh-group name {ip-address | name}
Configures an MSDP mesh group and indicates that an MSDP peer belongs to that mesh group.
Shutting Down an MSDP Peer
If you want to configure many MSDP commands for the same peer and you do not want the peer to go active, you can shut down the peer, configure it, and later bring it up.
You might also want to shut down an MSDP session without losing configuration information for the peer.
When in shutdown mode, the TCP connection is terminated and not restarted.
To shut down a peer, use the following command in global configuration mode:
ip msdp shutdown {peer-name | peer address}
Administratively shuts down the specified MSDP peer.
Including a Bordering PIM Dense-Mode Region in MSDP
You might have a router that borders a PIM sparse-mode region with a dense-mode region. By default, sources in the dense-mode region are not included in MSDP. You could configure this border router to send SA messages for sources active in the dense-mode region. If you do so, it is very important to also configure the ip msdp redistribute command to apply to only local sources. This can result in (S, G) state remaining long after a source in the dense-mode domain has stopped sending.
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To configure the border router to send SA messages for sources active in the dense-mode region, use the following command in global configuration mode
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Configuring an Originating Address Other Than the RP Address
If you want to change the Originator ID for any reason, use the ip msdp originator-id command in this section. For example, you might change the Originator ID in one of these cases:
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To allow an MSDP speaker that originates a Source-Active message to use its interface's IP address as the RP address in the SA message, use the following command in global configuration mode
ip msdp originator-id type number
Configures the RP address in SA messages to be the address of the originating router's interface.
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Monitoring and Maintaining MSDP
To monitor MSDP Source-Active messages, peers, state, or peer status, use the following commands in EXEC mode:
To clear MSDP connections, statistics, or SA cache entries, use the following commands in EXEC mode:
Configuration Examples
This section contains the following MSDP configurations examples:
Default MSDP Peer
The following example is a partial configuration of Router A and Router C in . Each of these ISPs may have more than one customer like the customer in the figure who use default peering (no BGP or MBGP). In that case, they may have similar configurations. That is, they will only accept SAs from a default peer if the SA is permited by the corresponding prefix list.
Router A
ip msdp default-peer 10.1.1.1ip msdp default-peer 10.1.1.1 prefix-list site-a ge 32ip prefix-list site-b permit 10.0.0.0/8Router C
ip msdp default-peer 10.1.1.1 prefix-list site-a ge 32ip prefix-list site-b permit 10.0.0.0/8Logical RP
The following example configures a logical RP using an MSDP mesh-group. The four routers that are logical RPs are RouterA, RouterB, RouterC, and RouterD. RouterE is an MSDP border router that is not an RP. illustrates the logical RP environment in this example; the configurations for routers A, B and E follow the figure.
It is important to note the use of the loopback interface and how those host routes are advertised in OSPF. It is also important to carefully choose the OSPF router ID loopback so the ID does not use the logical RP address.
In this example, all the logical RPs are on the same LAN, but this is not typical. The host-route for the RP address is advertised throughout the domain and each PIM DR in the domain joins to the closest RP. The RPs each share (S,G) information with each other by sending SA messages. Each logical RP must use a separate Originator-ID.
Note there are two MSDP mesh-groups on RouterA. The routes for the loopback interfaces are in OSPF. Loopback 0 is the Router ID and is used as the connect-source/update-source for MBGP/MSDP. Loopback 10 is the same on all routers in the example.
All networks are 171.69.0.0. The RP address is 10.10.10.10 on Loopback 10 on all RPs. BGP connections are 192.168.1.x on Loopback 0. Loopback 0 is put into BGP with network 192.168.1.3 mask 255.255.255.255 nlri unicast multicast.
Figure 3 Logical RP using MSDP
RouterA
!hostname RouterA!ip routing!ip subnet-zeroip multicast-routing!!interface Loopback0ip address 192.168.1.2 255.255.255.255no shutdown!interface Loopback10ip address 10.10.10.10 255.255.255.255no ip directed-broadcastip pim sparse-dense-modeno shutdown!interface Ethernet1/2description LANethernet2ip address 171.69.2.2 255.255.255.0ip pim sparse-dense-modeno shutdown!interface Ethernet4/0/0description LANethernet3ip address 171.69.3.2 255.255.255.0ip pim sparse-dense-modeno shutdown!router ospf 10network 171.69.0.0 0.0.255.255 area 0network 10.10.10.10 0.0.0.0 area 0network 192.168.1.2 0.0.0.0 area 0!router bgp 1no synchronizationnetwork 171.69.0.0 nlri unicast multicastnetwork 192.168.1.2 mask 255.255.255.255 nlri unicast multicastneighbor 192.168.1.3 remote-as 1 nlri unicast multicastneighbor description routerBneighbor 192.168.1.3 next-hop-selfneighbor 192.168.1.3 update-source loopback0neighbor 192.168.1.4 remote-as 1 nlri unicast multicastneighbor description routerCneighbor 192.168.1.4 update-source loopback0neighbor 192.168.1.5 remote-as 1 nlri unicast multicastneighbor description routerDneighbor 192.168.1.5 next-hop-selfneighbor 192.168.1.5 update-source loopback0neighbor 192.168.1.6 remote-as 1 nlri unicast multicastneighbor description routerEneighbor 192.168.1.6 update-source Loopback0neighbor 192.168.1.6 next-hop-self!!ip msdp peer 192.168.1.3 connect-source loopback 0ip msdp peer 192.168.1.5 connect-source loopback 0ip msdp peer 192.168.1.4 connect-source loopback 0ip msdp peer 192.168.1.6 connect-source Loopback0ip msdp mesh-group inside-test 192.168.1.3ip msdp mesh-group inside-test 192.168.1.4ip msdp mesh-group inside-test 192.168.1.5ip msdp mesh-group outside-test 192.168.1.6ip msdp originator-id loopback0!ip classlessip pim send-rp-disc scope 10ip pim send-rp-anno loopback 10 scope 10!RouterB
!hostname RouterB!ip routing!ip multicast-routingip dvmrp route-limit 20000!interface Loopback0ip address 192.168.1.3 255.255.255.255no shutdown!interface Loopback10ip address 10.10.10.10 255.255.255.255ip pim sparse-dense-modeno shutdown!interface Ethernet2description LANethernet 0ip address 171.69.0.3 255.255.255.0ip pim sparse-dense-modeno shutdown!interface Ethernet3description LANethernet 2ip address 171.69.2.3 255.255.255.0ip pim sparse-dense!router ospf 10network 171.69.0.0 0.0.255.255 area 0network 10.10.10.10 0.0.0.0 area 0network 192.168.1.3 0.0.0.0 area 0!router bgp 1no synchronizationnetwork 171.69.0.0 nlri unicast multicastnetwork 192.168.1.3 mask 255.255.255.255 nlri unicast multicastneighbor 192.168.1.2 remote-as 1 nlri unicast multicastneighbor description routerAneighbor 192.168.1.2 update-source loopback0neighbor 192.168.1.4 remote-as 1 nlri unicast multicastneighbor description routerCneighbor 192.168.1.4 update-source loopback0neighbor 192.168.1.5 remote-as 1 nlri unicast multicastneighbor description routerDneighbor 192.168.1.5 update-source loopback0neighbor 192.168.1.5 soft-recon in!ip msdp peer 192.168.1.2 connect-source loopback 0ip msdp peer 192.168.1.5 connect-source loopback 0ip msdp peer 192.168.1.4 connect-source loopback 0ip msdp mesh-group inside-test 192.168.1.2ip msdp mesh-group inside-test 192.168.1.4ip msdp mesh-group inside-test 192.168.1.5ip msdp originator-id loopback0!ip classlessip pim send-rp-disc scope 10ip pim send-rp-anno loopback 10 scope 10!RouterE
!hostname RouterE!ip routing!ip subnet-zeroip routingip multicast-routingip dvmrp route-limit 20000!interface Loopback0ip address 192.168.1.6 255.255.255.255no shutdown!interface Ethernet2description LANethernet 3ip address 171.69.3.6 255.255.255.0ip pim sparse-dense-modeno shutdown!interface Ethernet5description LANethernet 6ip address 192.169.1.6 255.255.255.0ip pim sparse-dense-modeip multicast boundary 20no shutdown!router ospf 10network 171.69.0.0 0.0.255.255 area 0network 192.168.1.6 0.0.0.0 area 0default-information originate metric-type 1!router bgp 1no synchronizationnetwork 171.69.0.0 nlri unicast multicastnetwork 192.168.1.6 mask 255.255.255.255 nlri unicast multicastnetwork 192.168.1.0neighbor 192.168.1.2 remote-as 1 nlri unicast multicastneighbor 192.168.1.2 update-source Loopback0neighbor 192.168.1.2 next-hop-selfneighbor 192.168.1.2 route-map 2-intern outneighbor 192.169.1.7 remote-as 2 nlri unicast multicastneighbor 192.169.1.7 route-map 2-extern outneighbor 192.169.1.7 default-originate!ip classlessip msdp peer 192.168.1.2 connect-source Loopback0ip msdp peer 192.169.1.7ip msdp mesh-group outside-test 192.168.1.2ip msdp originator-id Loopback0!access-list 1 permit 192.168.1.0access-list 1 deny 192.168.1.0 0.0.0.255access-list 1 permit any!route-map 2-extern permit 10match ip address 1!route-map 2-intern deny 10match ip address 1!Command Reference
This section documents the following new commands that configure MSDP. All other commands used in this document can be found in the Cisco IOS 12.0 command reference publications.
Note
In Cisco IOS Release 12.0(1)T or later, you can search and filter the output for show and more commands. This functionality is useful when you need to sort through large amounts of output, or if you want to exclude output that you do not need to see.
To use this functionality, enter a show or more command followed by the "pipe" character (|), one of the keywords begin, include, or exclude, and an expression that you want to search or filter on:
command | {begin | include | exclude} regular-expression
Following is an example of the show atm vc command in which you want the command output to begin with the first line where the expression "PeakRate" appears:
show atm vc | begin PeakRate
For more information on the search and filter functionality, refer to the Cisco IOS Release 12.0(1)T feature module titled CLI String Search.
clear ip msdp peer
To clear the TCP connection to the specified MSDP peer, use the clear ip msdp peer EXEC command.
clear ip msdp peer {ip-address | name}
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
This command closes the TCP connection to the peer, resets all the MSDP peer statistics, and clears the input and output queues to and from the MSDP peer.
Examples
The following example clears the TCP connection to the MSDP peer at 120.15.9.8:
clear ip msdp peer 120.15.9.8Related Commands
clear ip msdp sa-cache
To clear MSDP Source-Active cache entries, use the clear ip msdp sa-cache EXEC command.
clear ip msdp sa-cache [group-address | name]
Syntax Description
group-address | name
(Optional) Multicast group address or name for which Source-Active entries are cleared from the Source-Active cache.
Command Modes
EXEC
Command History
Usage Guidelines
In order to have any SA entries in the cache to clear, Source-Active caching must have been enabled with the ip msdp cache-sa-state command
If no multicast group is identified by group address or name, all SA cache entries are cleared.
Examples
The following example clears the Source-Active entries for the multicast group 224.5.6.7 from the cache:
clear ip msdp sa-cache 224.5.6.7Related Commands
Configures the router to create Source-Active state.
Displays (S,G) state learned by MSDP peers.
clear ip msdp statistics
To clear statistics counters for one or all of the MSDP peers without resetting the sessions, use the clear ip msdp statistics EXEC command.
clear ip msdp statistics [peer-address | name]
Syntax Description
peer-address | name
(Optional) Address or name of the MSDP peers whose statistics counters, reset count, and input/output count are cleared.
Command Modes
EXEC
Command History
Examples
The following example clears the counters for the peer named sanjose:
clear ip msdp statistics sanjoseip msdp border
To configure a router that borders a PIM sparse-mode region and dense-mode region to use MSDP, use the ip msdp border global configuration command. To prevent this action, use the no form of this command.
ip msdp border sa-address type number
no ip msdp border sa-address type number
Syntax Description
Defaults
The active sources in the dense-mode region will not participate in MSDP.
Command Modes
Global configuration
Command History
Usage Guidelines
Note
Use this command if you want the router to send Source-Active messages for sources active in the PIM dense-mode region to MSDP peers.
Note
Note that the ip msdp originator-id co
