• Allows a rendezvous point (RP) to dynamically discover active sources outside of its domain.
• Introduces a more manageable approach for building multicast distribution trees between multiple domains.

MSDP is a mechanism to connect multiple PIM-SM domains. The purpose of MSDP is to discover multicast sources in other PIM domains. The main advantage of MSDP is that it reduces the complexity of interconnecting multiple PIM-SM domains by allowing PIM-SM domains to use an interdomain source tree (rather than a common shared tree). When MSDP is configured in a network, RPs exchange source information with RPs in other domains. An RP can join the interdomain source tree for sources that are sending to groups for which it has receivers. The RP can do that because it is the root of the shared tree within its domain, which has branches to all points in the domain where there are active receivers. When a last-hop router learns of a new source outside the PIM-SM domain (through the arrival of a multicast packet from the source down the shared tree), it then can send a join toward the source and join the interdomain source tree.

Note	If the RP either has no shared tree for a particular group or a shared tree whose outgoing interface list is null, it does not send a join to the source in another domain.

When MSDP is enabled, an RP in a PIM-SM domain maintains MSDP peering relationships with MSDP-enabled routers in other domains. This peering relationship occurs over a TCP connection, where primarily a list of sources sending to multicast groups is exchanged. MSDP uses TCP (port 639) for its peering connections. As with BGP, using point-to-point TCP peering means that each peer must be explicitly configured. The TCP connections between RPs, moreover, are achieved by the underlying routing system. The receiving RP uses the source lists to establish a source path. If the multicast sources are of interest to a domain that has receivers, multicast data is delivered over the normal, source-tree building mechanism provided by PIM-SM. MSDP is also used to announce sources sending to a group. These announcements must originate at the RP of the domain.

Note	MSDP depends on BGP or multiprotocol BGP (MBGP) for interdomain operation. We recommended that you run MSDP on RPs sending to global multicast groups.

The figure illustrates MSDP operating between two MSDP peers. PIM uses MSDP as the standard mechanism to register a source with the RP of a domain.

Figure 1

MSDP Running Between RP Peers

When MSDP is implemented, the following sequence of events occurs:

1. When a PIM designated router (DR) registers a source with its RP as illustrated in the figure, the RP sends a Source-Active (SA) message to all of its MSDP peers.

Note

The DR sends the encapsulated data to the RP only once per source (when the source goes active). If the source times out, this process happens again when it goes active again. This situation is different from the periodic SA message that contains all sources that are registered to the originating RP. Those SA messages are MSDP control packets, and, thus, do not contain encapsulated data from active sources.

1. The SA message identifies the source address, the group that the source is sending to, and the address or the originator ID of the RP, if configured.
2. Each MSDP peer that receives the SA message floods the SA message to all of its peers downstream from the originator. In some cases (such as the case with the RPs in PIM-SM domains B and C in the figure), an RP may receive a copy of an SA message from more than one MSDP peer. To prevent looping, the RP consults the BGP next-hop database to determine the next hop toward the originator of the SA message. If both MBGP and unicast BGP are configured, MBGP is checked first, and then unicast BGP. That next-hop neighbor is the RPF-peer for the originator. SA messages that are received from the originator on any interface other than the interface to the RPF peer are dropped. The SA message flooding process, therefore, is referred to as peer-RPF flooding. Because of the peer-RPF flooding mechanism, BGP or MBGP must be running in conjunction with MSDP.

Note	(M)BGP is not required in MSDP mesh group scenarios. For more information about MSDP mesh groups, see the Configuring an MSDP Mesh Group section.

Note	(M)BGP is not required in default MSDP peer scenarios or in scenarios where only one MSDP peer is configured. For more information, see the Configuring a Default MSDP Peer section.

1. When an RP receives an SA message, it checks to see whether there are any members of the advertised groups in its domain by checking to see whether there are interfaces on the group's (*, G) outgoing interface list. If there are no group members, the RP does nothing. If there are group members, the RP sends an (S, G) join toward the source. As a result, a branch of the interdomain source tree is constructed across autonomous system boundaries to the RP. As multicast packets arrive at the RP, they are then forwarded down its own shared tree to the group members in the RP's domain. The members' DRs then have the option of joining the rendezvous point tree (RPT) to the source using standard PIM-SM procedures.
2. The originating RP continues to send periodic SA messages for the (S, G) state every 60 seconds for as long as the source is sending packets to the group. When an RP receives an SA message, it caches the SA message. Suppose, for example, that an RP receives an SA message for (172.16.5.4, 228.1.2.3) from originating RP 10.5.4.3. The RP consults its mroute table and finds that there are no active members for group 228.1.2.3, so it passes the SA message to its peers downstream of 10.5.4.3. If a host in the domain then sends a join to the RP for group 228.1.2.3, the RP adds the interface toward the host to the outgoing interface list of its (*, 224.1.2.3) entry. Because the RP caches SA messages, the router will have an entry for (172.16.5.4, 228.1.2.3) and can join the source tree as soon as a host requests a join.

Note	In all current and supported software releases, caching of MSDP SA messages is mandatory and cannot be manually enabled or disabled. By default, when an MSDP peer is configured, the ip multicast cache-sa-state command will automatically be added to the running configuration.

There are four basic MSDP message types, each encoded in their own Type, Length, and Value (TLV) data format.

• SA Messages
  
• SA Request Messages
  
• SA Response Messages
  
• Keepalive Messages
  

The section describes SA message origination, receipt, and processing in detail.

• SA Message Origination
  
• SA Message Receipt
  
• SA Message Processing
  

Like BGP, MSDP establishes neighbor relationships with other MSDP peers. MSDP peers connect using TCP port 639. The lower IP address peer takes the active role of opening the TCP connection. The higher IP address peer waits in LISTEN state for the other to make the connection. MSDP peers send keepalive messages every 60 seconds. The arrival of data performs the same function as the keepalive message and keeps the session from timing out. If no keepalive messages or data is received for 75 seconds, the TCP connection is reset.

The MSDP MD5 password authentication feature is an enhancement to support Message Digest 5 (MD5) signature protection on a TCP connection between two MSDP peers. This feature provides added security by protecting MSDP against the threat of spoofed TCP segments being introduced into the TCP connection stream.

• How MSDP MD5 Password Authentication Works
  
• Benefits of MSDP MD5 Password Authentication
  

The ip msdp sa-limit command is used to limit the overall number of SA messages that a router can accept from specified MSDP peers. When the ip msdp sa-limit command is configured, the router maintains a per-peer count of SA messages stored in the SA cache and will ignore new messages from a peer if the configured SA message limit for that peer has been reached.

The ip msdp sa-limit command was introduced as a means to protect an MSDP-enabled router from denial of service (DoS) attacks. We recommended that you configure SA message limits for all MSDP peerings on the router. An appropriately low SA limit should be configured on peerings with a stub MSDP region (for example, a peer that may have some further downstream peers but that will not act as a transit for SA messages across the rest of the Internet). A high SA limit should be configured for all MSDP peerings that act as transits for SA messages across the Internet.

The ip msdp keepalive command is used to adjust the interval at which an MSDP peer will send keepalive messages and the interval at which the MSDP peer will wait for keepalive messages from other peers before declaring them down.

Once an MSDP peering session is established, each side of the connection sends a keepalive message and sets a keepalive timer. If the keepalive timer expires, the local MSDP peer sends a keepalive message and restarts its keepalive timer; this interval is referred to as the keepalive interval. The keepalive-intervalargument is used to adjust the interval for which keepalive messages will be sent. The keepalive timer is set to the value specified for the keepalive-intervalargument when the peer comes up. The keepalive timer is reset to the value of the keepalive-interval argument whenever an MSDP keepalive message is sent to the peer and reset when the timer expires. The keepalive timer is deleted when an MSDP peering session is closed. By default, the keepalive timer is set to 60 seconds.

Note	The value specified for the keepalive-interval argument must be less than the value specified for the holdtime-intervalargument and must be at least one second.

The hold-time timer is initialized to the value of the hold-time-interval argument whenever an MSDP peering connection is established, and is reset to the value of the hold-time-intervalargument whenever an MSDP keepalive message is received. The hold-time timer is deleted whenever an MSDP peering connection is closed. By default, the hold-time interval is set to 75 seconds.

Use the hold-time-interval argument to adjust the interval at which the MSDP peer will wait for keepalive messages from other peers before declaring them down.

The ip msdp timer command is used to adjust the interval at which all MSDP peers will wait after peering sessions are reset before attempting to reestablish the peering sessions. This interval is referred to as the connection-retry interval. By default, MSDP peers will wait 30 seconds after the session is reset before attempting to reestablish sessions with other peers. When the ip msdp timer command is configured, the configured connection-retry interval applies to all MSDP peering sessions on the router.

When the MSDP Compliance with IETF RFC 3618 feature is configured, the peer-RPF forwarding rules defined in IETF RFC 3618 are applied to MSDP peers. IETF RFC 3618 provides peer-RPF forwarding rules that are used for forwarding SA messages throughout an MSDP-enabled internet. Unlike the RPF check used when forwarding data packets, which compares a packet's source address against the interface upon which the packet was received, the peer-RPF check compares the RP address carried in the SA message against the MSDP peer from which the message was received. Except when MSDP mesh groups are being used, SA messages from an RP address are accepted from only one MSDP peer to avoid looping SA messages.

Note	For more information about the MSDP peer-forwarding rules defined in RFC 3618, see RFC 3618, Multicast Source Discovery Protocol (MSDP) .

• Benefits of MSDP Compliance with RFC 3618
  

In most scenarios, an MSDP peer is also a BGP peer. If an autonomous system is a stub or nontransit autonomous system, and particularly if the autonomous system is not multihomed, there is little or no reason to run BGP to its transit autonomous system. A static default route at the stub autonomous system, and a static route pointing to the stub prefixes at the transit autonomous system, is generally sufficient. But if the stub autonomous system is also a multicast domain and its RP must peer with an RP in the neighboring domain, MSDP depends on the BGP next-hop database for its peer-RPF checks. You can disable this dependency on BGP by defining a default peer from which to accept all SA messages without performing the peer-RPF check, using the ip msdp default-peer command. A default MSDP peer must be a previously configured MSDP peer.

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 Router B is connected to the Internet through two Internet service providers (ISPs), one that owns Router A and the other that owns Router 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, 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 the first default peer in the configuration, it will be used if it is up and running. Only if Router A is not running 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 router. 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.

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, it will be used if it is up and running. Only when Router A is not running 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.

An MSDP mesh group is a group of MSDP speakers that have fully meshed MSDP connectivity between one another. In other words, each of the MSDP peers in the group must have an MSDP peering relationship (MSDP connection) to every other MSDP peer in the group. When an MSDP mesh group is configured between a group of MSDP peers, SA message flooding is reduced. Because when an MSDP peer in the group receives an SA message from another MSDP peer in the group, it assumes that this SA message was sent to all the other MSDP peers in the group. As a result, it is not necessary for the receiving MSDP peer to flood the SA message to the other MSDP peers in the group.

• Benefits of MSDP Mesh Groups
  

By default, an RP that is configured to run MSDP will originate SA messages for all local sources for which it is the RP. Local sources that register with an RP, therefore, will be advertised in SA messages, which in some cases is not desirable. For example, if sources inside a PIM-SM domain are using private addresses (for example, network 10.0.0.0/8), you should configure an SA origination filter to restrict those addresses from being advertised to other MSDP peers across the Internet.

To control what sources are advertised in SA messages, you can configure SA origination filters on an RP using the ip msdp redistribute command. By creating SA origination filters, you can control the sources advertised in SA messages as follows:

• You can prevent an RP from originating SA messages for local sources by configuring the ip msdp redistribute command without any keywords or arguments. Issuing this form of the command effectively prevents the router from advertising local sources in SA messages.

Note	When the ip msdp redistribute command is entered without any keywords or arguments, the router will still forward SA messages from other MSDP peers in the normal fashion; it will just not originate any SA messages for local sources.

• You can configure the router to originate SA messages only for (S, G) pairs defined in an extended access list by configuring the ip msdp redistribute command with the optional list keyword and access-list argument. Issuing the form of the command effectively configures the router to only originate SA messages for local sources sending to specific groups that match (S, G) pairs defined in the extended access list. All other local sources will not be advertised in SA messages.
• You can configure the router to originate SA messages only for AS paths defined in an AS-path access list by configuring the ip msdp redistribute command with the optional asn keyword and as-access-list argument. Issuing this form of the command effectively configures the router to only originate SA messages for local sources sending to specific groups that the match AS paths defined in an AS-path access list. All other local sources will not be advertised in SA messages.

Note	AS-path access lists are configured using the ip as-path access-list command.

You can configure the router to originate SA messages only for local sources that match the criteria defined in a route map by configuring the ip msdp redistributecommand with the optional route-map keyword and map-name argument. Issuing this form of the command effectively configures the router to only originate SA messages for local sources that match the criteria defined in the route map. All other local sources will not be advertised in SA messages.

Note	You can configure an SA origination filter that includes an extended access list, an AS-path access list, and route map (or a combination thereof). In that case, all conditions must be true before any local sources are advertised in SA messages.

By default, an MSDP-enabled router 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 using the ip msdp sa-filter out command. Outgoing filter lists (configured using the ip msdp sa-filter outcommand) apply to all SA messages, whether locally originated or received from another MSDP peer, whereas SA origination filters (configured using the ip msdp redistribute command) apply only to locally originated SA messages. For more information about using the ip msdp redistribute command to enable a filter for MSDP SA messages originated by the local router, see the Controlling SA Messages Originated by an RP for Local Sources section.

By creating an outgoing filter list, you can control the SA messages that a router forwards to a peer as follows:

• You can filter all outgoing SA messages forwarded to a specified MSDP peer by configuring the ip msdp filter-sa-request outcommand without any keywords or arguments. Issuing this form of the command effectively configures the router 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 ip msdp sa-filter outcommand with the optional list keyword and access-list argument. Issuing the form of the command effectively configures the router 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 ip msdp sa-filter outcommand with the optional route-map keyword and map-name argument. Issuing this form of the command effectively configures the router 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 ip msdp sa-filter outcommand with the optional rp-list keyword and list argument or with the rp-route-map keyword map-nameargument. This type of outgoing filter list enables the router 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.

Note	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 that case, all conditions must be true for the MSDP peer to forward the outgoing SA message.

Caution

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.

By default, an MSDP-enabled router receives all SA messages sent to it from its MSDP peers. However, you can control the source information that a router receives from its MSDP peers by creating incoming filter lists using the ip msdp sa-filter in command.

By creating incoming filter lists, you can control the incoming SA messages that a router receives from its peers as follows:

• You can filter all incoming SA messages from a specified MSDP peer by configuring the ip msdp filter-sa-request in command without any keywords or arguments. Issuing this form of the command effectively configures the router 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 ip msdp sa-filter in command with the optional list keyword and access-list argument. Issuing the form of the command effectively configures the router to only receive SA messages from the MSDP peer that match the (S, G) pairs defined in the extended access list. All other incoming SA messages from the MSDP peer will be ignored.
• You can filter a subset of incoming SA request messages from a specified peer based on match criteria defined in a route map by configuring the ip msdp sa-filter incommand with the optional route-map keyword and map argument. Issuing this form of the command effectively configures the router to only receive SA messages that match the criteria defined in the route map. All other incoming SA messages from the MSDP peer will be ignored.
• You can filter a subset of incoming SA messages from a specified peer based on both (S, G) pairs defined in an extended access list and on match criteria defined in a route map by configuring the ip msdp sa-filter incommand with the optional list keyword and access-list argument and with the optional route-map keyword and map-name argument. Issuing this form of the command configures the router to only receive incoming SA messages that both match the (S, G) pairs defined in the extended access list and match the criteria defined in the route map. All other incoming SA messages from the MSDP peer will be ignored.
• You can filter a subset of incoming SA messages from a specified peer based on the announcing RP address contained in the SA message by configuring the ip msdp sa-filter in command with the optional rp-list keyword and list argument or with the rp-route-map map-name. This type of incoming filter list enables the router to filter incoming SA messages based on their origin, even after the SA message may have already been transmitted across one or more MSDP peers.

Note	You can configure an incoming filter list that includes an extended access list, a route map, and either an RP access list or an RP route map. In that case, all conditions must be true for the MSDP peer to receive the incoming SA message.

Caution

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, incoming filter lists are used only to reject undesirable sources, such as sources using private addresses.

The time-to-live (TTL) value provides a means to limit the number of hops a packet can take before being dropped. The ip multicast ttl-threshold command is used to specify a TTL for data-encapsulated SA messages sent to specified MSDP peers. By default, multicast data packets in SA messages are sent to an MSDP peer, provided the TTL value of the packet is greater than 0, which is standard TTL behavior.

In general, a TTL-threshold problem can be introduced by the encapsulation of a source's initial multicast packet in an SA message. Because the multicast packet is encapsulated inside of the unicast SA message (whose TTL is 255), its TTL is not decremented as the SA message travels to the MSDP peer. Furthermore, the total number of hops that the SA message traverses can be drastically different than a normal multicast packet because multicast and unicast traffic may follow completely different paths to the MSDP peer and hence the remote PIM-SM domain. As a result, encapsulated packets can end up violating TTL thresholds. The solution to this problem is to configure a TTL threshold that is associated with any multicast packet that is encapsulated in an SA message sent to a particular MSDP peer using the ip multicast ttl-threshold command. The ip msdp ttl-threshold command prevents any multicast packet whose TTL in the IP header is less than the TTL value specified for the ttl-valueargument from being encapsulated in SA messages sent to that peer.

The ip msdp sa-request command is used to enable a noncaching router to send SA request messages to a specified MSDP peer. You can enter this command multiple times to specify that the router send SA request messages to additional MSDP peers.

If an noncaching RP has an MSDP peer that is caching SAs, you can reduce the join latency for a noncaching peer by enabling the noncaching peer to send SA request messages. When a host requests a join to a particular group, the noncaching RP sends an SA request message to its caching peers. If a peer has cached source information for the group in question, it sends the information to the requesting RP with an SA response message. The requesting RP uses the information in the SA response but does not forward the message to any other peers. If a noncaching RP receives an SA request, it sends an error message back to the requestor.

Note

In all current and supported Cisco IOS software releases, caching of MSDP SA messages is mandatory and cannot be manually enabled or disabled. By default, when an MSDP peer is configured, the ip multicast cache-sa-state command will automatically be added to the running configuration. Prior to Cisco IOS Releases 12.1(7) and 12.0(14)S1, caching of SAs was disabled by default and could be enabled with the ip msdp cache-sa-state command.

By default, a router honors all outgoing SA request messages from its MSDP peers; that is, it sends cached source information to requesting MSDP peers in SA response messages. You can control the outgoing SA request messages that a router will honor from specified peers by enabling an SA request filter using the ip msdp filter-sa-request command. By creating an SA request filter, you can control the outgoing SA requests that the router will honor from MSDP peers as follows:

• You can filter all SA request messages from a specified peer by configuring the ip msdp filter-sa-request command without the optional list keyword and access-listargument. Issuing this form of the ip msdp filter-sa request command effectively configures the router to ignore all SA requests from the specified MSDP peer.
• You can filter a subset of SA request messages from a specified peer based on groups defined in a standard access list by configuring the ip msdp filter-sa-requestcommand with the optional list keyword and access-list argument. Issuing the form of the command effectively configures the router to honor only SA request messages from the MSDP peer that match the groups defined in a standard access list. SA request messages from the specified peer for other groups will be ignored.

The MSDP MIB describes managed objects that can be used to remotely monitor MSDP speakers using SNMP. The MSDP MIB module contains four scalar objects and three tables. The tables are the Requests table, the Peer table, and the Source-Active (SA) Cache table. The Cisco implementation supports the Peer table and SA Cache table only. The Requests table contains information used to determine which peer to send SA requests to. However, the MSDP implementation used in Cisco IOS software does not associate sending SA requests to peers with group addresses (or group address masks).

Note	The MSDP-MIB.my file can be downloaded from the Cisco MIB website on Cisco.com at the following URL: http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml .

Before You Begin

• This task assumes that you have enabled IP multicast routing and have configured PIM-SM.
• With the exception of a single MSDP peer, default MSDP peer, and MSDP mesh group scenarios, all MSDP peers must be configured to run BGP prior to being configured for MSDP.

Note	By enabling an MSDP peer, you implicitly enable MSDP.

1.    enable

2.    configure terminal

3.    ip msdp peer {peer-name| peer-address} [connect-source type number] [remote-as as-number]

4.    ip msdp description {peer-name| peer-address} text

5.    end

1.    enable

2.    configure terminal

3.    ip msdp shutdown {peer-name | peer-address}

4.    Repeat Step 3 to shut down additional MSDP peers.

5.    end

1.    enable

2.    configure terminal

3.    ip msdp password peer {peer-name | peer-address} [encryption-type] string

4.    end

5.    show ip msdp peer [peer-address | peer-name]

• Troubleshooting Tips
  

Perform this optional (but highly recommended) task to limit the overall number of SA messages that the router can accept from specified MSDP peers. Performing this task protects an MSDP-enabled router from distributed denial-of-service (DoS) attacks.

Note	We recommend that you perform this task for all MSDP peerings on the router.

1.    enable

2.    configure terminal

3.    ip msdp sa-limit {peer-address | peer-name} sa-limit

4.    Repeat Step 3 to configure SA limits for additional MSDP peers.

5.    end

6.    show ip msdp count [as-number]

7.    show ip msdp peer [peer-address | peer-name]

8.    show ip msdp summary

Perform this optional task to adjust the interval at which an MSDP peer will send keepalive messages and the interval at which the MSDP peer will wait for keepalive messages from other peers before declaring them down. By default, it may take as long as 75 seconds for an MSDP peer to detect that a peering session with another MSDP peer has gone down. In network environments with redundant MSDP peers, decreasing the hold-time interval (by lowering the value for the hold-time-interval argument of the ip msdp keepalive command from the default of 75 seconds) can expedite the reconvergence time of MSDP peers in the event that an MSDP peer fails.

Note

We recommend that you do not change the command defaults for the ip msdp keepalive command, because the command defaults are in accordance with RFC 3618, Multicast Source Discovery Protocol . If your network environment requires that you modify the defaults, you must configure the same time values for the keepalive-interval and hold-time-interval arguments on both ends of the MSDP peering session.

1.    enable

2.    configure terminal

3.    ip msdp keepalive {peer-address | peer-name} keepalive-interval hold-time-interval

4.    Repeat Step 3 to adjust the keepalive message interval for additional MSDP peers.

5.    end

1.    enable

2.    configure terminal

3.    ip msdp timer connection-retry-interval

4.    end

1.    enable

2.    configure terminal

3.    ip msdp rpf rfc3618

4.    end

5.    show ip msdp rpf-peer rp-address

1.    enable

2.    configure terminal

3.    ip msdp default-peer {peer-address | peer-name} [prefix-list list]

4.    end

Perform this optional task to configure an MSDP mesh group.

Note	You can configure multiple mesh groups per router.

1.    enable

2.    configure terminal

3.    ip msdp mesh-group mesh-name {peer-address | peer-name}

4.    Repeat Step 3 to add MSDP peers as members of the mesh group.

5.    end

Perform this task to control SA messages originated by an RP by enabling a filter to restrict which registered sources are advertised in SA messages.

Note	For best practice information related to configuring MSDP SA message filters, see the Multicast Source Discovery Protocol SA Filter Recommendations tech note.

1.    enable

2.    configure terminal

3.    ip msdp redistribute [list access-list] [asn as-access-list] [route-map map-name]

4.    end

Perform this optional task to control the forwarding of SA messages to MSDP peers by configuring outgoing filter lists.

Note	For best practice information related to configuring MSDP SA message filters, see the Multicast Source Discovery Protocol SA Filter Recommendations tech note.

1.    enable

2.    configure terminal

3.    ip msdp sa-filter out {peer-address | peer-name} [list access-list] [route-map map-name] [rp-list access-list | rp-route-map map-name]

4.    Repeat Step 3 to configure outgoing filter lists for additional MSDP peers.

5.    end

Perform this optional task to control the receipt of incoming SA messages from MSDP peers.

Note	For best practice information related to configuring MSDP SA message filters, see the Multicast Source Discovery Protocol SA Filter Recommendations tech note.

1.    enable

2.    configure terminal

3.    ip msdp sa-filter in {peer-address | peer-name} [list access-list] [route-map map-name] [rp-list access-list | rp-route-map map-name]

4.    Repeat Step 3 to configure incoming filter lists for additional MSDP peers.

5.    end

1.    enable

2.    configure terminal

3.    ip msdp ttl-threshold {peer-address | peer-name} ttl-value

4.    end

Perform this optional task to enable a router to request source information from MSDP peers.

Note	Because SA caching is enabled by default and cannot be explicitly enabled or disabled in Cisco IOS Release 12.1(7) and 12.0(14)S1 and later Cisco IOS software releases, performing this task is seldom needed.

1.    enable

2.    configure terminal

3.    ip msdp sa-request {peer-address | peer-name}

4.    Repeat Step 3 to specify that the router send SA request messages to additional MSDP caching peers.

5.    end

1.    enable

2.    configure terminal

3.    ip msdp filter-sa-request {peer-address | peer-name} [list access-list]

4.    Repeat Step 3 to configure SA request filters for additional MSDP peers.

5.    end

Perform this optional task to configure a border router to send SA messages for sources active in a PIM dense mode (PIM-DM) region.

You might have a router that borders a PIM-SM region and a PIM-DM region. By default, sources in the PIM-DM domain are not included in MSDP. You could configure this border router to send SA messages for sources active in the PIM-DM domain. If you do so, it is very important to also configure the ip msdp redistribute command to control what local sources from the PIM-DM domain are advertised. Not configuring this command can result in the (S, G) state remaining long after a source in the PIM-DM domain has stopped sending.

Note	For more information about using the ip msdp redistribute command to control the sources advertised in SA messages, see the Controlling SA Messages Originated by an RP for Local Sources section.

1.    enable

2.    configure terminal

3.    ip msdp border sa-address type number

4.    end

1.    enable

2.    configure terminal

3.    ip msdp originator-id type number

4.    end

1.    enable

2.    debug ip msdp [peer-address | peer-name] [detail] [routes]

3.    debug ip msdp resets

4.    show ip msdp count [as-number]

5.    show ip msdp peer [peer-address | peer-name]

6.    show ip msdp sa-cache [group-address | source-address | group-name | source-name] [as-number]

7.    show ip msdp summary

Router# enable

Router# debug ip msdp
MSDP debugging is on
Router#
MSDP: 224.150.44.254: Received 1388-byte message from peer
MSDP: 224.150.44.254: SA TLV, len: 1388, ec: 115, RP: 172.31.3.92 
MSDP: 224.150.44.254: Peer RPF check passed for 172.31.3.92, used EMBGP peer
MSDP: 224.150.44.250: Forward 1388-byte SA to peer
MSDP: 224.150.44.254: Received 1028-byte message from peer
MSDP: 224.150.44.254: SA TLV, len: 1028, ec: 85, RP: 172.31.3.92 
MSDP: 224.150.44.254: Peer RPF check passed for 172.31.3.92, used EMBGP peer
MSDP: 224.150.44.250: Forward 1028-byte SA to peer
MSDP: 224.150.44.254: Received 1388-byte message from peer
MSDP: 224.150.44.254: SA TLV, len: 1388, ec: 115, RP: 172.31.3.111 
MSDP: 224.150.44.254: Peer RPF check passed for 172.31.3.111, used EMBGP peer
MSDP: 224.150.44.250: Forward 1388-byte SA to peer
MSDP: 224.150.44.250: Received 56-byte message from peer
MSDP: 224.150.44.250: SA TLV, len: 56, ec: 4, RP: 192.168.76.241 
MSDP: 224.150.44.250: Peer RPF check passed for 192.168.76.241, used EMBGP peer
MSDP: 224.150.44.254: Forward 56-byte SA to peer
MSDP: 224.150.44.254: Received 116-byte message from peer
MSDP: 224.150.44.254: SA TLV, len: 116, ec: 9, RP: 172.31.3.111 
MSDP: 224.150.44.254: Peer RPF check passed for 172.31.3.111, used EMBGP peer
MSDP: 224.150.44.250: Forward 116-byte SA to peer
MSDP: 224.150.44.254: Received 32-byte message from peer
MSDP: 224.150.44.254: SA TLV, len: 32, ec: 2, RP: 172.31.3.78 
MSDP: 224.150.44.254: Peer RPF check passed for 172.31.3.78, used EMBGP peer
MSDP: 224.150.44.250: Forward 32-byte SA to peer

Router# debug ip msdp resets

Router# show ip msdp count
SA State per Peer Counters, <Peer>: <# SA learned>
    192.168.4.4: 8
SA State per ASN Counters, <asn>: <# sources>/<# groups>
    Total entries: 8
    ?: 8/8

Router# show ip msdp peer 192.168.4.4
MSDP Peer 192.168.4.4 (?), AS 64512 (configured AS)
  Connection status:
    State: Up, Resets: 0, Connection source: Loopback0 (2.2.2.2)
    Uptime(Downtime): 00:07:55, Messages sent/received: 8/18
    Output messages discarded: 0
    Connection and counters cleared 00:08:55 ago
  SA Filtering:
    Input (S,G) filter: none, route-map: none
    Input RP filter: none, route-map: none
    Output (S,G) filter: none, route-map: none
    Output RP filter: none, route-map: none
  SA-Requests: 
    Input filter: none
  Peer ttl threshold: 0
  SAs learned from this peer: 8
  Input queue size: 0, Output queue size: 0
  MD5 signature protection on MSDP TCP connection: not enabled

Router# show ip msdp sa-cache
MSDP Source-Active Cache - 8 entries
(10.44.44.5, 239.232.1.0), RP 192.168.4.4, BGP/AS 64512, 00:01:20/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.1), RP 192.168.4.4, BGP/AS 64512, 00:01:20/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.2), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.3), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.4), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.5), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.6), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4
(10.44.44.5, 239.232.1.7), RP 192.168.4.4, BGP/AS 64512, 00:01:19/00:05:32, Peer 192.168.4.4

Router# show ip msdp summary
MSDP Peer Status Summary
Peer Address     AS    State    Uptime/  Reset SA    Peer Name
                                Downtime Count Count
192.168.4.4      4     Up       00:08:05 0     8     ?

1.    enable

2.    clear ip msdp peer [peer-address | peer-name]

3.    clear ip msdp statistics [peer-address | peer-name]

4.    clear ip msdp sa-cache [group-address]

Before You Begin

• This task assumes that you have configured SNMP and MSDP on your devices.
• In each PIM-SM domain there should be a device that is configured as the MSDP speaker. This device must have SNMP and the MSDP MIB enabled.

Note	All MSDP-MIB objects are implemented as read-only. The Requests table is not supported in Cisco's implementation of the MSDP MIB. The msdpEstablished notification is not supported in Cisco's implementation of the MSDP MIB. >

1.    enable

2.    snmp-server enable traps msdp

3.    snmp-server host host [traps | informs] [version {1 | 2c | 3 [auth| priv | noauth]}] community-string [udp-port port-number] msdp

4.    end

• Troubleshooting Tips