Usage Guidelines

Using the ip pgm host command without a keyword or an argument enables PGM Host on the router and configures the router to source PGM packets through a virtual host interface.

Specifying a physical or logical interface type (for example, an Ethernet, serial, or loopback interface) with the ip pgm host source-interface command configures the router to source PGM packets out of the physical or logical interface.

Note	You must first enable PGM Host globally on the router using the ip pgm host command before sourcing PGM packets out of a physical or logical interface using the ip pgm host source-interface command.

Sourcing PGM packets through a virtual host interface enables the router to send and receive PGM packets through any router interface. The virtual host interface also serves as the interface to the multicast applications that reside at the PGM network layer.

Sourcing IP multicast traffic out a specific physical or logical interface configures the router to send PGM packets out that interface only and to receive packets on any router interface.

When both PGM Host and Router Assist are enabled on the router, the router can process received PGM packets as a virtual PGM Host, originate PGM packets and serve as its own first hop PGM network element, and forward received PGM packets. Refer to the “Configuring PGM Host and Router Assist” chapter of the Cisco IOS IP Configuration Guide for more information about PGM Router Assist.

The table below lists the available parameters for the connection-parameter argument. The parameters should be configured only by experts in PGM technology. Use the no ip pgm host connection-parameter command to return a parameter to its default value.

Usage Guidelines

This command is highly recommended for optimal deployment of PGM Reliable Transport Protocol on a host.

Usage Guidelines

Enabling PIM on an interface also enables Internet Group Management Protocol (IGMP) operation on that interface. An interface can be configured to be in dense mode, passive mode, sparse mode, or sparse-dense mode. The mode describes how the Cisco IOS software populates its multicast routing table and how the software forwards multicast packets that it receives from its directly connected LANs. Dense mode interfaces are always added to the table when the multicast routing table is populated. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers, or there is a directly connected member on the interface.

In Cisco IOS XE Release 3.2S and later releases, when PIM is enabled on an interface but the ip multicast-routing command has not been configured, a warning message, informing the user that the ip multicast-routing command is not configured and that multicast packets will not be forwarded, is no longer displayed.

Dense Mode

Initially, a dense mode interface forwards multicast packets until the router determines that there are group members or downstream routers, or until a prune message is received from a downstream router. Then, the dense mode interface periodically forwards multicast packets out the interface until the same conditions occur. Dense mode assumes that multicast group members are present. Dense mode routers never send a join message. They do send prune messages as soon as they determine they have no members or downstream PIM routers. A dense mode interface is subject to multicast flooding by default.

Dense Mode with Proxy Registering

For a router in a PIM sparse mode (PIM-SM) domain configured to operate in sparse mode or sparse-dense mode, the ip pim dense-mode proxy-register command must be configured on the interface leading toward the bordering dense mode region. This configuration will enable the router to register traffic from the dense mode region with the rendezvous point (RP) in the sparse mode domain.

Prior to Cisco IOS Release 12.0S, an RP needed to be running on the border router leading toward a dense mode region so that the RP could learn about traffic from sources in the dense mode region.

This command requires an extended access list or route map argument specifying which traffic the router needs to register with the RP. This command applies only to sources reachable through a PIM router. Cisco IOS software will always register traffic from remote sources if it arrives on a dense mode interface and if the Reverse Path Forwarding (RPF) neighbor leading toward the source is a Distance Vector Multicast Routing Protocol (DVMRP) but not a PIM router. This functionality has existed since Cisco IOS Release 10.0 and cannot be modified (restricted) with an access list or route map.

Passive Mode

An interface configured with passive mode does not pass or forward PIM control plane traffic; it passes or forwards only IGMP traffic. If passive mode is configured on an interface enabled for IP multicast, the router will not send PIM messages on the interface nor will it accept PIM messages from other routers on this interface. The router acts as the only PIM router on the network and works as the designated router (DR) and the designated forwarder (DF) for all Bidirectional PIM group ranges.

The ip pim neighbor-filter command has no effect and is superseded by the ip pim passive command when both commands are configured on the same interface.

Do not use the ip pim passive command on LANs that have more than one IP multicast router connected to them, because all routers with this command become DR and DF, resulting in duplicate traffic (PIM-SM, PIM-DM, PIM-SSM) or looping traffic (Bidir-PIM). To limit PIM messages to and from valid routers on LANs with more than one router, use the ip pim neighbor-filter command

Sparse Mode

A sparse mode interface is used for multicast forwarding only if a join message is received from a downstream router or if group members are directly connected to the interface. Sparse mode assumes that no other multicast group members are present. When sparse mode routers want to join the shared path, they periodically send join messages toward the RP. When sparse mode routers want to join the source path, they periodically send join messages toward the source; they also send periodic prune messages toward the RP to prune the shared path.

Sparse-Dense Mode

An alternative to choosing just dense mode or just sparse mode is to run PIM in a single region in sparse mode for some groups and dense mode for other groups.

In sparse-dense mode, if the group is in dense mode, the interface will be treated as dense mode. If the group is in sparse mode, the interface will be treated in sparse mode. The group is “sparse” if the router knows about an RP for that group.

When an interface is treated in dense mode, it is populated in the outgoing interface list of the multicast routing table when either of the following conditions is true:

• Members or DVMRP neighbors are on the interface.

• Any of the PIM neighbors on the interface have not pruned for the group.

When an interface is treated in sparse mode, it is populated in the outgoing interface list of the multicast routing table when either of the following conditions is true:

• Members or DVMRP neighbors are on the interface.

• A PIM neighbor on the interface has received an explicit join message.

Usage Guidelines

Use this command to prevent unauthorized sources from registering with the RP. If an unauthorized source sends a register message to the RP, the RP will immediately send back a register-stop message.

The access list or route map provided for the ip pim accept-register command should only filter on IP source addresses and IP destination addresses. Filtering on other fields (for example, IP protocol or UDP port number) will not be effective and may cause undesired traffic to be forwarded from the RP down the shared tree to multicast group members. If more complex filtering is desired, use the ip multicast boundary command instead.

Note	If the RP is also the first hop designated router (DR) for directly connected sources, PIM register packets will not be filtered using the ip pim accept-register command. For this case, use the ip multicast boundary command to filter the directly connected source traffic.

Usage Guidelines

This command causes the router to accept only (*, G) join messages destined for the specified RP address. Additionally, the group address must be in the range specified by the access list.

When the rp-address argument is one of the addresses of the system, the system will be the RP only for the specified group range specified by the access list. When the group address is not in the group range, the RP will not accept join or register messages and will respond immediately to register messages with register-stop messages.

Usage Guidelines

Use this command to enable the receiving device in an IP multicast network to accept a (*, G) Join from an unexpected (different) RP address.

Before enabling PIM Allow RP, you must first use the ip pim rp-address command to define an RP.

Usage Guidelines

Use the ip pim autorp listener command with interfaces configured for PIM sparse mode operation in order to establish a network configuration where Auto-RP operates in PIM dense mode and multicast traffic can operate in sparse mode, bidirectional mode, or Source Specific Multicast (SSM) mode.

Usage Guidelines

Bidir-PIM is disabled by default to ensure complete backward compatibility when upgrading a router to Cisco IOS Release 12.0(18)ST or a later release.

When bidir-PIM is disabled, the router will behave similarly to a router without bidir-PIM support. The following conditions will apply:

• PIM hello messages sent by the router will not contain the bidirectional mode option.

• The router will not send designated forwarder (DF) election messages and will ignore DF election messages it receives.

• The ip pim rp-address, ip pim send-rp-announce , and ip pim rp-candidate global configuration commands will be treated as follows:

  • If these commands are configured when bidir-PIM is disabled, bidirectional mode will not be a configuration option.
  • If these commands are configured with the bidirectional mode option when bidir-PIM is enabled and then bidir-PIM is disabled, these commands will be removed from the command-line interface (CLI). In this situation, these commands must be configured again with the bidirectional mode option when bidir-PIM is reenabled.

• The df keyword for the s how ip pim interface user EXEC or privileged EXEC command and debug ip pim privileged EXEC command is not supported.

Usage Guidelines

Normally, DF election only occurs on those interfaces on which all Protocol Independent Multicast (PIM) neighbors are bidir capable. To allow for a smoother transition from a sparse-mode only network to a hybrid bidir-/sparse-mode network, the ip pim bidir-neighbor-filter command enables you to specify what routers should be participating on the DF election, while still allowing all routers to participate in the sparse-mode domain.

Bidirectional PIM allows multicast routers to keep reduced state information. All of the multicast routers in a segment must be bidirectionally enabled in order for bidir to elect a DF. Because routers in a segment are not always bidir-enabled, a mechanism is necessary to allow these routers to elect a DF from those routers on a segment that are bidir-enabled.

Multicast boundaries on the nonbidir routers are defined to prevent PIM messages and data for the bidir groups to leak in or out of the bidir subset cloud. Meanwhile, the bidir routers can elect a DF from among themselves even when there are nonbidir routers in the segment.

The ip pim bidir-neighbor-filter command allows the use of an ACL to specify which neighbors will participate in the DF election, allowing bidir deployment in the necessary routers without having to upgrade all of the routers in the segment.

Default behavior is that all routers are considered to be bidir-capable. Therefore, if one neighbor does not support bidir, the DF election will not occur.

When the ip pim bidir-neighbor-filter command is enabled, the routers that are permitted by the ACL are considered to be bidir-capable. Therefore:

• If a permitted neighbor does not support bidir, the DF election will not occur.

• If a denied neighbor does not support bidir, DF election still occurs among all other routers on the segment.

Usage Guidelines

When this command is configured on an interface, no Protocol Independent Multicast (PIM) Version 2 BSR messages will be sent or received through the interface. Configure an interface bordering another PIM domain with this command to avoid BSR messages from being exchanged between the two domains. BSR messages should not be exchanged between different domains, because routers in one domain may elect rendezvous points (RPs) in the other domain, resulting in protocol malfunction or loss of isolation between the domains.

Note	This command does not set up multicast boundaries. It sets up only a PIM domain BSR message border.

Usage Guidelines

This command configures the router to send BSR messages to all its PIM neighbors, with the address of the designated interface as the BSR address.

Note	The interface specified for this command must be enabled for Protocol Independent Multicast (PIM) using the ip pim command.

This command should be configured on backbone routers that have good connectivity to all parts of the PIM domain.

The BSR mechanism is specified in RFC 2362. Candidate RP (C-RP) routers unicast C-RP advertisement packets to the BSR. The BSR then aggregates these advertisements in BSR messages, which it regularly multicasts with a TTL of 1 to the ALL-PIM-ROUTERS group address, 224.0.0.13. The multicasting of these messages is handled by hop-by-hop RPF flooding; so no preexisting IP multicast routing setup is required (unlike with AutoRP). In addition, the BSR does not preselect the designated RP for a particular group range (unlike AutoRP); instead, each router that receives BSR messages will elect RPs for group ranges based on the information in the BSR messages.

Note	Cisco routers always accept and process BSR messages. There is no command to disable this function.

Cisco routers perform the following steps to determine which C-RP is used for a group:

1. A longest match lookup is performed on the group prefix that is announced by the BSR C-RPs.

2. If more than one BSR-learned C-RP are found by the longest match lookup, the C-RP with the lowest priority (configured with the ip pim rp-candidate command) is preferred.

3. If more than one BSR-learned C-RP have the same priority, the BSR hash function is used to select the RP for a group.

4. If more than one BSR-learned C-RP return the same hash value derived from the BSR hash function., the BSR C-RP with the highest IP address is preferred.

Usage Guidelines

Use this command to filter BSR C-RP advertisements at the BSR using an ACL.

The interface specified for this command must be enabled for Protocol Independent Multicast (PIM) using the ip pim command.

This command should be configured on backbone routers that have good connectivity to all parts of the PIM domain.

Usage Guidelines

If you use IP multicast in mission-critical networks, you should avoid the use of PIM-DM (dense mode).

Dense mode fallback describes the event of the PIM mode changing (falling back) from sparse mode (which requires an RP) to dense mode (which does not use an RP). Dense mode fallback occurs when RP information is lost.

If all interfaces are configured with the ip pim sparse-mode command, there is no dense mode fallback because dense mode groups cannot be created over interfaces configured for sparse mode.

Use the no ip pim dm-fallback command to disable PIM-DM flooding on sparse-dense interfaces.

Cause and Effect of Dense Mode Fallback

PIM determines whether a multicast group operates in PIM-DM or PIM-SM mode based solely on the existence of RP information in the group-to-RP mapping cache. If Auto-RP is configured or a bootstrap router (BSR) is used to distribute RP information, there is a risk that RP information can be lost if all RPs, Auto-RP, or the BSR for a group fails due to network congestion. This failure can lead to the network either partially or fully falling back into PIM-DM.

If a network falls back into PIM-DM and AutoRP or BSR is being used, dense mode flooding will occur. Routers that lose RP information will fallback into dense mode and any new states that must be created for the failed group will be created in dense mode.

Effects of Preventing Dense Mode Fallback

Prior to the introduction of PIM-DM fallback prevention, all multicast groups without a group-to-RP mapping would be treated as dense mode.

With the introduction of PIM-DM fallback prevention, the PIM-DM fallback behavior has been changed to prevent dense mode flooding. By default, if all of the interfaces are configured to operate in PIM sparse mode (using the ip pim sparse-mode command), there is no need to configure the no ip pim dm-fallback command (that is, the PIM-DM fallback behavior is enabled by default). If any interfaces are not configured using the ip pim sparse-mode command (for example, using the ip pim sparse-dense-mode command), then the PIM-DM fallback behavior can be explicit disabled using the no ip pim dm-fallback command.

When the no ip pim dm-fallback command is configured or when ip pim sparse-mode is configured on all interfaces, any existing groups running in sparse mode will continue to operate in sparse mode but will use an RP address set to 0.0.0.0. Multicast entries with an RP address set to 0.0.0.0 will exhibit the following behavior:

• Existing (S, G) states will be maintained.

• No PIM Join or Prune messages for (*, G) or (S, G, RPbit) are sent.

• Received (*, G) or (S, G, RPbit) Joins or Prune messages are ignored.

• No registers are sent and traffic at the first hop is dropped.

• Received registers are answered with register stop.

• Asserts are unchanged.

• The (*, G) outgoing interface list (olist) is maintained only for the Internet Group Management Protocol (IGMP) state.

• Multicast Source Discovery Protocol (MSDP) source active (SA) messages for RP 0.0.0.0 groups are still accepted and forwarded.

Usage Guidelines

When a DR is a candidate for election, the following conditions apply:

• The router with the highest priority value configured on an interface will be elected as the DR. If this priority value is the same on multiple routers, then the router with the highest IP address configured on an interface will be elected as the DR.

• If a router does not advertise a priority value in its hello messages, the router is regarded as having the highest priority and will be elected as the DR. If there are multiple routers with this priority status, then the router with the highest IP address configured on an interface will be elected as the DR.

Usage Guidelines

This command enables syslog messages that help to generate a list of neighbor state changes.

Usage Guidelines

Use this command to limit the number of group-to-RP mappings that can be created. When the specified maximum number of mappings is reached, existing mappings are updated but new mappings cannot be created.

Use the show ip pim rp mapping command to display the count and limit for mappings when this command is configured and there are mappings created.

Usage Guidelines

This command applies to an ATM interface only and also requires IP Protocol Independent Multicast sparse mode (PIM-SM).

An idling policy uses the ip pim vc-count number command to limit the number of VCs created by PIM. When the router stays at or below this number, no idling policy is in effect. When the next VC to be opened will exceed the number, an idling policy is exercised. Any virtual circuits with a traffic rate lower than the ip pim minimum-vc-rate command are subject to the idling policy.

Usage Guidelines

This command is accepted only on an ATM interface. It allows optimal multicast trees to be built down to ATM switch granularity. This command can enhance router performance and link utilization because packets are not replicated and sent multiple times over the ATM interface.

Usage Guidelines

Use this command on Frame Relay, Switched Multimegabit Data Service (SMDS), or ATM only, especially when these media do not have native multicast available. Do not use this command on multicast-capable LANs such as Ethernet or FDDI.

When this command is configured, each Protocol Independent Multicast (PIM) join message is tracked in the outgoing interface list of a multicast routing table entry. Therefore, only PIM WAN neighbors that have joined for the group will get packets sent as data-link unicasts. This command should only be used when the ip pim sparse-mode command is configured on the interface. This command is not recommended for LANs that have natural multicast capabilities.

This command is used only when hubs and spokes are disjointly located in a different segment. This command cannot be used in a full mesh topology where the spokes are directly connected to each other.

Usage Guidelines

If the ip pim passive command is configured on an interface enabled for IP multicast, the router will operate this interface in PIM passive mode, which means that the router will not send PIM messages on the interface nor will it accept PIM messages from other routers across this interface. The router will instead consider that it is the only PIM router on the network and thus act as the Designated Router (DR) and also as the Designated Forwarder (DF) for all bidirectional PIM (bidir-PIM) group ranges. Operations of the Interior Gateway Management Protocol (IGMP) are unaffected by this command.

Note

Do not use the ip pim passive command on LANs that have more than one multicast router connected to them because all routers with this command configured will consider themselves to be DR/DF, resulting in duplicate traffic (for PIM sparse mode [PIM-SM], PIM dense mode [PIM-DM], and Source Specific Multicast [PIM-SSM]) or even in looping traffic (for bidir-PIM). Instead, use the ip pim neighbor-filter command to limit PIM messages to and from valid routers on LANs with more than one router.

Note	The ip pim passive and ip pim neighbor-filter commands can be used together on an interface. If both commands are configured, the ip pim passive command will take precedence over the ip pim neighbor-filter command.

Use the show ip pim interface command to confirm the mode that PIM interfaces are operating in.

Usage Guidelines

Use this command to configure the frequency of PIM neighbor discovery messages. By default these messages are sent once every 30 seconds. In PIM Version 1 (PIMv1), these messages are referred to as PIM query messages; in PIM Version 2 (PIMv2), these messages are referred to as PIM hello messages. By default, routers run PIMv2 and send PIM hello messages. A router will change (auto-fallback) to PIMv1 and will send PIM query messages if it detects a neighboring router that only supports PIMv1. As soon as that neighboring PIMv1 router is removed from the network, the router will revert to PIMv2.

Note	A router can be configured to exclusively use PIMv1 on an interface with the ip pim version 1 command.

Note	In PIM version 2, PIM hello messages also contain a variety of options that allow PIM routers on the network to learn about the capabilities of PIM neighbors. For more information about these capabilities, see the show ip pim neighbor command page.

PIM neighbor discovery messages are used to determine which router on a network is acting as the Designated Router (DR) for PIM sparse mode (PIM-SM) and Source Specific Multicast (SSM). The DR is responsible for joining PIM-SM and SSM groups receiving multicast traffic from sources requested by receivers (hosts). In addition, in PIM-SM, the DR is also responsible for registering local sources with the RP. If the DR fails, a backup router will become the DR and then forward traffic for local receivers and register local sources.

The period argument is used to specify the PIM hello (query) interval. The interval determines the frequency at which PIM hello (query) messages are sent.

Note

When an interfaces enabled for PIM comes up, a PIM hello (query) message is sent immediately. In some cases, the initial PIM hello (query) message may be lost.If the first PIM hello (query) does not get sent when an interface initially comes up, another one will be sent 3 seconds later regardless of the PIM hello (query) interval to ensure that there are no initialization delays.

The configured PIM hello interval also determines the holdtime used by a PIM router. The Cisco IOS software calculates the holdtime as follows:

3 * the interval specified for the period argument

By default, PIM routers announce the holdtime in PIM hello (query) messages.If the holdtime expires and another router has not received another hello (query) message from this router, it will timeout the PIM neighbor. If the timed out router was the DR, the timeout will trigger DR election. By default, the DR-failover interval occurs after 90 seconds (after the default holdtime expires for a DR). To reduce DR-failover time in redundant networks, a lower value for the period argument can be configured on all routers. The minimum DR-failover time that can be configured (in seconds) is 3 seconds (when the period argument is set to 1 second). The DR-failover time can be reduced to less than 3 seconds if the msecs keyword is specified. When the msecs keyword is used with the ip pim query-interval command, the value specified for the period argument is interpreted as a value in milliseconds (instead of seconds). By enabling a router to send PIM hello messages more often, this functionality allows the router to discover unresponsive neighbors more quickly. As a result, the router can implement failover or recovery procedures more efficiently

Note	If IGMP Version 1 is being used on a network, then the DR is also the IGMP querier; if at least IGMP version 2 is being used, then the router with the lowest IP address becomes the IGMP querier.

Usage Guidelines

Use this command to enable PIM redundancy on an interface and assign a redundancy priority value to the PIM DR.

The redundancy priority for a PIM DR must be greater than the configured or default value (1) of the PIM DR priority (value used to elect a device as PIM DR) on any device for which the same HSRP group is enabled or the HSRP Active will fail to win the DR election. The value for PIM DR priority is configured by using the ip pim dr-priority command. The default value of PIM DR priority is 1.

Use the standby ip command in interface configuration mode to activate HSRP and define an HSRP group on an interface.

Because HSRP group names are case sensitive, the value of the group argument in the ip pim redundancy group command must match the value in the standby ip name configuration for the HSRP group.

If the value of the group argument in the ip pim redundancy group command is invalid, the command will be accepted but a debug message will be issued indicating that the specified HSRP group does not exist.

Note	We recommend that you always configure the standby ip name command when configuring an HSRP group to be used for HSRP aware PIM.

Usage Guidelines

Use this command to rate limit the PIM-SM register packets based on either packets per second or bits per second. Enabling this command will limit the load on the DR and RP at the expense of dropping those register packets that exceed the set limit. Receivers may experience data packet loss within the first second in which register packets are sent from bursty sources.

Setting a value for the packets-per-second argument using the ip pim register-rate-limit command sets rate limiting on all PIM-SM registers.

Setting a value for the bits-per-second argument using the ip pim register-rate-limit command sets rate limiting on PIM-SM registers on a per-RP basis.

If the ip pim command is configured with the dense-mode and proxy-register keywords, you must set a limit on the maximum number of PIM-SM register packets sent because of the potentially large number of sources from the dense mode area that may send data into the sparse mode region (and thus need registering in the border router).

This command applies only to sparse mode (S, G) multicast routing entries.

Usage Guidelines

This command is required only when the IP source address of a register message is not a uniquely routed address to which the RP can send packets. This situation may occur if the source address is filtered such that packets sent to it will not be forwarded or if the source address is not unique to the network. In these cases, the replies sent from the RP to the source address will fail to reach the DR, resulting in Protocol Independent Multicast sparse mode (PIM-SM) protocol failures.

If no IP source address is configured or if the configured source address is not in service, the IP address of the outgoing interface of the DR leading toward the RP is used as the IP source address of the register message. Therefore, we recommend using a loopback interface with an IP address that is uniquely routed throughout the PIM-SM domain.

Usage Guidelines

In the Cisco IOS implementation of PIM, each multicast group individually operates in one of the following modes: dense mode, sparse mode, or bidirectional mode. Groups in sparse mode (PIM-SM) or bidirectional mode (bidir-PIM) use RPs to connect sources and receivers. All routers in a PIM domain need to have a consistent configuration for the mode and RP addresses of the multicast groups.

The Cisco IOS software learns the mode and RP addresses of multicast groups through the following three mechanisms: static group-to-RP mapping configurations, Auto-RP, and bootstrap router (BSR). By default, groups will operate in dense mode. No commands explicitly define groups to operate in dense mode.

Use the ip pim rp-address command to statically define the RP address for PIM-SM or bidir-PIM groups (an ip pim rp-address command configuration is referred to as a static group-to-RP mapping).

You can configure a single RP for more than one group using an access list. If no access list is specified, the static RP will map to all multicast groups, 224/4.

You can configure multiple RPs, but only one RP per group range.

If multiple ip pim rp-address commands are configured, the following rules apply:

• Highest RP IP address selected regardless of reachability: If a multicast group is matched by the access list of more than one configured ip pim rp-address command, then the RP for the group is determined by the RP with the highest RP address configured.

• One RP address per command: If multiple ip pim rp-address commands are configured, each static group-to-RP mapping must be configured with a unique RP address (if not, it will be overwritten).This restriction also means that only one RP address can be used to provide RP functions for either sparse mode or bidirectional mode groups. If you want to configure static group-to-RP mappings for both bidirectional and sparse mode, the RP addresses must be unique for each mode.

• One access list per command: If multiple ip pim rp-address commands are configured, only one access list can be configured per static group-to-RP mapping. An access list cannot be reused with other static group-to-RP mappings configured on a router.

• For the Cisco Catalyst 6500 Series switch: Overlapping group ranges are not supported when they are configured for PIM-SM and bidir-PIM modes on a Cisco Catalyst 6500. Avoid overlapping group ranges when configuring both the PIM-SM and bidir-PIM modes in the same configuration. For more information, see the Cisco Catalyst 6500 configuration example below.

If dynamic and static group-to-RP mappings are used together, the following rule applies to a multicast group: Dynamic group-to-RP mappings take precedence over static group-to-RP mappings--unless the override keyword is used.

Usage Guidelines

Use the ip pim rp-announce-filter command to filter incoming Auto-RP announcement messages sent from C-RPs to RP mapping agents. This command should only be configured on RP mapping agents.

Auto-RP provides a means to distribute group-to-RP mappings within a multicast network without having to manually configure static RPs on every router. To accomplish this distribution, Auto-RP uses the following mechanisms:

• C-RPs send RP announcements to multicast group 224.0.1.39.

• RP mapping agents receive the RP announcements from C-RPs and determine which C-RP should be the RP for any given group (or groups) based on the highest IP address. RP mapping agents then distribute that information to all multicast routers by means of RP discovery messages, which are sent to the Auto-RP multicast group address 224.0.1.40.

• The sending of both RP announcements and RP discovery messages occurs every 60 seconds by default with a holdtime of 180 seconds. If no RP is found, each router then searches locally for a static RP mapping. If no static RP mapping is configured, the router defaults to dense mode.

The ip pim rp-announce filter command allows you to configure policies on an RP mapping agent that define the C-RPs whose RP announcements are to be filtered (ignored) by the mapping agent. You can use this command to configure the mapping agent to filter RP announcement messages from specific or unknown routers by permitting or denying specific C-RPs .You can also filter RP announcement messages from an candidate RP for specific group prefixes, thereby restricting that router to be the C-RP for only the ranges not filtered on the RP mapping agent.

Caution

If you use more than one RP-mapping agent, you must configure the same filters on all mapping agents to avoid inconsistencies in Auto-RP operations.

Caution

An improperly configured ip pim rp-announce-filter command may result in RP announcements being ignored. In addition, the ip pim rp-announce-filter command should only be configured on the mapping agent; if not, the command will fail because non-mapping agents do not listen to group 224.0.1.39 and do not know how to distribute the necessary group-to-RP mappings.

Use the rp-list keyword and access-list argument to specify the standard access list that defines the IP addresses of C-RPs whose RP announcements are to be permitted or denied on the RP mapping agent. Use the group-list keyword and access-list argument to specify the standard access list that defines the multicast groups to be permitted or denied from RP announcements sent by C-RPs to the RP mapping agent. RP announcment messages received that match the access list specified for rp-list keyword and access list specified for the group-list keyword are filtered by the RP mapping agent.

If a C-RP list is not specified (using the rp-list keyword and access-list argument), the command will permit all C-RPs. If a group list is not specified (using the group-list keyword and access-list argument), the command will deny all groups.

If no ip pim rp-announce-filter commands are configured, a router enabled to be an RP mapping agent (using the ip pim send-rp-discovery command) will accept all RP announcements for all groups from all C-RPs. Configure one or more ip pim rp-announce-filter commands on RP mapping agents to filter unwanted RP messages.

Usage Guidelines

Use this command to configure the router to send PIMv2 messages that advertise itself as a candidate RP to the BSR.

This command should be configured on backbone routers that have good connectivity to all parts of the PIM domain.

The IP address associated with the interface specified for the interface-type and interface-number arguments will be advertised as the C-RP address.

Note	The interface specified for this command must be enabled for Protocol Independent Multicast (PIM) using the ip pim command.

If the optional group-list keyword and access-list argument are configured, the group prefixes defined by the standard IP access list will also be advertised in association with the RP address.

Use this command with the optional bidir keyword when you want bidirectional forwarding and you are using the PIM Version 2 BSR mechanism to distribute group-to-RP mappings. Other options are as follows:

• If you are using Auto-RP to distribute group-to-RP mappings, use the bidir keyword with the ip pim send-rp-announce command.

• If you are not distributing group-to-RP mappings using either Auto-RP or the PIMv2 BSR mechanism, use the bidir keyword with the ip pim rp-address command.

When the interval keyword is specified, the C-RP advertisement interval is set to a value specified by the seconds argument. The default interval is 60 seconds. Reducing this interval to a time of less than 60 seconds can reduce the time required to fail over to a secondary RP at the expense of generating more PIMv2 messages.

When the priority keyword is specified, the router will announce itself to be a C-RP with the priority specified for the value argument. For more information about the BSR selection process, see the ip pim bsr-candidate command page.

Usage Guidelines

Enter this command on the router that you want to be an RP. When you are using Auto-RP to distribute group-to-RP mappings, this command causes the router to send an Auto-RP announcement message to the well-known group CISCO-RP-ANNOUNCE (224.0.1.39). This message announces the router as a candidate RP for the groups in the range described by the access list.

Use this command with the bidir keyword when you want bidirectional forwarding and you are using Auto-RP to distribute group-to-RP mappings. Other options are as follows:

• If you are using the PIM Version 2 bootstrap router (PIMv2 BSR) mechanism to distribute group-to-RP mappings, use the bidir keyword with the ip pim rp-candidate command.

• If you are not distributing group-to-RP mappings using either Auto-RP or the PIMv2 BSR mechanism, use the bidir keyword with the ip pim rp-address command.

Usage Guidelines

Use the ip pim send-rp-discovery command to configure the router to be an RP mapping agent. An RP mapping agent receives Auto-RP announcement messages, which it stores in its local group-to-RP mapping cache. The RP mapping agent uses the information contained in the Auto-RP announcement messages to elect the RP. The RP mapping agent elects the candidate RP with the highest IP address as the RP for a group range.

The required scope keyword and ttl-value argument are used to specify the TTL value in the IP header of Auto-RP discovery messages.

Note	For the scope keyword and ttl-value argument, specify a TTL large enough to cover your Protocol Independent Multicast (PIM) domain.

The optional interval keyword and seconds argument are used to specify the interval at which Auto-RP discovery messages are sent. By default, Auto-RP discovery messages are sent at an interval of 60 seconds or when the RP mapping agent detects changes.

Note

Lowering the interval at which Auto-RP discovery messages are sent from the default value of 60 seconds results in more frequent floodings of the group-to-RP mappings. In some network environments, the disadvantages of lowering the interval (more control packet overhead) may outweigh the advantages (more frequent group-to-RP mapping updates).

When Auto-RP is used, the following events occur:

1. The RP mapping agent listens for Auto-RP announcement messages sent by candidate RPs to the well-known group address CISCO-RP-ANNOUNCE (224.0.1.39).

2. The RP mapping agents stores the information learned from Auto-RP announcement messages in its local group-to-RP mapping cache.

3. The RP mapping agents elects the candidate RP with the highest IP address as the RP and announces the RP in the Auto-RP discovery messages that it sends out.

4. The Auto-RP discovery messages that the RP mapping agent sends to the well-known group CISCO-RP-DISCOVERY (224.0.1.40), which Cisco routers join by default, contains the elected RP learned from the RP mapping agent’s group-to-RP mapping cache.

5. PIM designated routers listen for the Auto-RP discovery messages sent to 224.0.1.40 to learn the RP and store the information about the RP in their local group-to-RP mapping caches.

Use the show ip pim rp command with the mapping keyword to display all the group-to-RP mappings that the router has learned from Auto-RP.

Usage Guidelines

PIM snooping is not supported on groups that use the reserved MAC address range, for example, 0100.5e00.00xx, as an alias.

When you disable PIM snooping globally, PIM snooping is disabled on all VLANs.

Usage Guidelines

PIM snooping is not supported on groups that use the reserved MAC address range, for example, 0100.5e00.00xx, as an alias.

You must enable PIM snooping globally before enabling PIM snooping on an interface. To enable PIM snooping globally, use the ip pim snooping command in global configuration mode. When you disable PIM snooping globally, PIM snooping is disabled on all VLANs.

You can enable PIM snooping on VLAN interfaces only.

Usage Guidelines

PIM snooping is not supported on groups that use the reserved MAC address range, for example, 0100.5e00.00xx, as an alias.

Enter the no ip pim snooping dr-flood command only on switches that have no designated routers attached.

The designated router is programmed automatically in the (S,G) O-list.

Usage Guidelines

If a shared tree and SPT diverge in a VLAN on your switch router, and you have PIM snooping configured, then duplicate multicast packets may be delivered in your network. PIM snooping may stop the prune message sent by the receiver from reaching the upstream switch router in the shared tree, which causes more than one upstream switch router to forward the multicast traffic. This situation causes duplicate multicast packets to be delivered to the receivers. The sending of duplicate multicast packets only lasts a couple of seconds because the PIM-ASSERT mechanism is initiated and stops the extraneous flow. However, the cycle repeats itself when the next prune message is sent. To stop this situation from occurring, enter the no ip pim snooping suppress sgr-prune command.

Usage Guidelines

Use the ip pim sparse sg-expire-timer command to adjust the expiry timer interval for PIM-SM (S, G) mroute entries to a time value greater than the default expiry timer interval of 180 seconds. This command can be used to lock down the shortest-path tree (SPT) for intermittent sources in PIM-SM network environments, such as sources in trading floor environments that sporadically send financial data streams to multicast groups during trading floor hours.

When a source stops sending traffic to a multicast group, the corresponding (S, G) mroute entry eventually times out and the (S, G) entry is removed. When the source resumes sending traffic to the group, the (S, G) entry is rebuilt. During the short time interval before the (S, G) entry is rebuilt, the traffic is forwarded on the (*, G) forwarding entry. There is a small window of time before the (S, G) entry is completely built in which packets may be dropped. The ip pim sparse sg-expiry-timer command can be used to maintain the (S, G) entry so that it will not be removed and the stream will not potentially suffer packet loss.

Note	The ip pim sparse sg-expire-timer command only applies to PIM-SM (S, G) mroute entries and, thus, does not apply to PIM-SM (*, G) mroute entries.

Usage Guidelines

If a source sends at a rate greater than or equal to traffic rate (the kbps value), a PIM join message is triggered toward the source to construct a source tree.

If the infinity keyword is specified, all sources for the specified group will use the shared tree. Specifying a group-list access-list indicates the groups to which the threshold applies.

If the traffic rate from the source drops below the threshold traffic rate, the leaf router will switch back to the shared tree and send a prune message toward the source.

Usage Guidelines

When an SSM range of IP multicast addresses is defined by the ip pim ssm command, no Multicast Source Discovery Protocol (MSDP) Source-Active (SA) messages will be accepted or originated in the SSM range.

Usage Guidelines

Configuring this command removes PIM dense mode state refresh information from PIM hello messages.

Usage Guidelines

Configure this command on the interfaces of the first hop, PIM dense mode routers that are directly connected to sources for PIM-DM multicast groups.

In Cisco IOS Release 15.1(1)S and later releases, this command can be configured on an interface on which PIM sparse mode is enabled.

In Cisco IOS Release 15.1(0)S and earlier releases, this command can be configured on an interface only if PIM dense mode state refresh is enabled. If you attempt to configure this command on an interface on which PIM sparse mode is enabled, the following warning message is displayed.

Warning: PIM State-Refresh cannot be configured on sparse interface

By default, the processing and forwarding of PIM dense mode state refresh control messages is enabled on PIM routers that are running a Cisco IOS software release that supports PIM dense mode state refresh.