Implementing Multicast Routing on Cisco IOS XR Software
Multicast routing is a bandwidth-conserving
technology that reduces traffic by simultaneously delivering a single stream of
information to potentially thousands of corporate recipients and homes.
Applications that take advantage of multicast routing include video
conferencing, corporate communications, distance learning, and distribution of
software, stock quotes, and news.
This document assumes
that you are familiar with IPv4
routing configuration tasks and concepts for
Cisco IOS XR Software .
allows a host to send packets to a subset of all hosts as a group transmission
rather than to a single host, as in unicast transmission, or to all hosts, as
in broadcast transmission. The subset of hosts is known as
and are identified by a single multicast group address that falls under the IP
Class D address range from 126.96.36.199 through 188.8.131.52.
for Configuring Multicast Routing on the
Cisco NCS 6000 Series Routers
feature was introduced.
Implementing Multicast Routing
You must install
and activate the multicast
You must be in a user group associated with a task group that
includes the proper task IDs. The command reference guides include the task IDs
required for each command. If you suspect user group assignment is preventing
you from using a command, contact your AAA administrator for assistance.
To use this command, you must
be in a user group associated with a task group that includes appropriate task
IDs. If the user group assignment is preventing you from using a command,
contact your AAA administrator for assistance.
You must be
familiar with IPv4
routing configuration tasks and concepts.
must be operational.
Information About Implementing Multicast Routing
Key Protocols and
Features Supported in the Cisco IOS XR Software Multicast Routing
communication allows a host to send packets to a single host (unicast
to all hosts (broadcast
Multicast provides a third scheme, allowing a host to send a single data stream
to a subset of all hosts (group
about the same time. IP hosts are known as group members.
Packets delivered to
group members are identified by a single multicast group address. Multicast
packets are delivered to a group using best-effort reliability, just like IP
environment consists of senders and receivers. Any host, regardless of whether
it is a member of a group, can send to a group. However, only the members of a
group receive the message.
A multicast address is
chosen for the receivers in a multicast group. Senders use that group address
as the destination address of a datagram to reach all members of the group.
Membership in a
multicast group is dynamic; hosts can join and leave at any time. There is no
restriction on the location or number of members in a multicast group. A host
can be a member of more than one multicast group at a time.
How active a multicast
group is and what members it has can vary from group to group and from time to
time. A multicast group can be active for a long time, or it may be very
short-lived. Membership in a group can change constantly. A group that has
members may have no activity.
applications involve multiple participants. Multicast is naturally suitable for
this communication paradigm.
Cisco IOS XR Software supports the following protocols to
implement multicast routing:
between hosts on a LAN and the routers on that LAN to track the
multicast groups of which hosts are members.
Independent Multicast in sparse mode (PIM-SM) is used between routers so that
they can track which multicast packets to forward to each other and to their
directly connected LANs.
Independent Multicast in Source-Specific Multicast (PIM-SSM) is similar to
PIM-SM with the additional ability to report interest in receiving packets from
specific source addresses (or from all but the specific source addresses), to
an IP multicast address.
is a variant of the Protocol Independent Multicast suit of routing protocols
for IP multicast. PIM-BIDIR is designed to be used for many-to-many
applications within individual PIM domains.
This image shows
IGMP and PIM-SM
operating in a multicast environment.
Figure 1. Multicast
PIM-SM, PIM-SSM, and
Multicast (PIM) is a multicast routing protocol used to create multicast
distribution trees, which are used to forward multicast data packets. PIM is an
efficient IP routing protocol that is “independent” of a routing table, unlike
other multicast protocols such as Multicast Open Shortest Path First (MOSPF) or
Distance Vector Multicast Routing Protocol (DVMRP).
Cisco IOS XR Software supports Protocol Independent
Multicast in sparse mode (PIM-SM), Protocol Independent Multicast in
Source-Specific Multicast (PIM-SSM), and Protocol Independent Multicast in
Bi-directional mode (BIDIR) permitting these modes to operate on your router at
the same time.
PIM-SM and PIM-SSM
supports one-to-many applications by greatly simplifying the protocol mechanics
for deployment ease. Bidir PIM helps deploy emerging communication and
financial applications that rely on a many-to-many applications model. BIDIR
PIM enables these applications by allowing them to easily scale to a very large
number of groups and sources by eliminating the maintenance of source state.
PIM in sparse mode operation is used in a multicast network when relatively few routers are involved in each multicast and these routers do not forward multicast packets for a group, unless there is an explicit request for the traffic.
For more information about PIM-SM, see the PIM-Sparse Mode.
PIM in Source-Specific
Multicast operation uses information found on source addresses for a multicast
group provided by receivers and performs source filtering on traffic.
PIM-SSM operates in the 184.108.40.206/8 multicast group range for IPv4
. To configure these values,
If SSM is deployed
in a network already configured for PIM-SM, only the last-hop routers must be
Cisco IOS XR Software that supports the SSM feature.
No MSDP SA
messages within the SSM range are accepted, generated, or forwarded.
PIM-SM and PIM-SSM, and PIM BIDIR
within the SSM range of addresses change to PIM-SSM. In this mode, only PIM
(S,G) join and prune messages are generated by the router, and no (S,G) RP
shared tree or (*,G) shared tree messages are generated.
To report multicast
memberships to neighboring multicast routers, hosts use IGMP, and all routers
on the subnet must be configured with the same version of IGMP.
A router running
Cisco IOS XR Software does not automatically detect Version
1 systems. You must use the
in router IGMP configuration submode to configure the IGMP version.
Cisco IOS XR Software provides support for Internet Group
Management Protocol (IGMP) over IPv4
a means for hosts to indicate which multicast traffic they are
interested in and for routers to control and limit the flow of multicast
traffic throughout the network. Routers build state by means of IGMP
messages; that is, router queries and host reports.
A set of queries and
hosts that receive multicast data streams from the same source is called a
Hosts use IGMP
messages to join and leave multicast groups.
IGMP messages use
group addresses, which are Class D IP addresses. The high-order four bits of a
Class D address are 1110. Host group addresses can be in the range 220.127.116.11 to
18.104.22.168. The address 22.214.171.124 is guaranteed not to be assigned to any
group. The address 126.96.36.199 is assigned to all systems on a subnet. The
address 188.8.131.52 is assigned to all routers on a subnet.
The following points describe IGMP versions 1, 2, and 3:
IGMP Version 1 provides for the basic query-response mechanism that allows the multicast router to determine which multicast groups are active and for other processes that enable hosts to join and leave a multicast group.
IGMP Version 2 extends IGMP allowing such features as the IGMP query timeout and the maximum query-response time. See RFC 2236.
IGMP Routing Example
Figure 1 illustrates two sources, 10.0.0.1 and 10.0.1.1, that are multicasting to group 184.108.40.206. The receiver wants to receive traffic addressed to group 220.127.116.11 from source 10.0.0.1 but not from source 10.0.1.1. The host must send an IGMPv3 message containing a list of sources and groups (S, G) that it wants to join and a list of sources and groups (S, G) that it wants to leave. Router C can now use this information to prune traffic from Source 10.0.1.1 so that only Source 10.0.0.1 traffic is being delivered to
Figure 2. IGMPv3 Signaling
When configuring IGMP, ensure that all systems on the subnet support the same IGMP version. The router does not automatically detect Version 1 systems. Configure the router for Version 2 if your hosts do not support Version 3.
Multicast (PIM) is a routing protocol designed to send and receive multicast
routing updates. Proper operation of multicast depends on knowing the unicast
paths towards a source or an RP. PIM relies on unicast routing protocols to
derive this reverse-path forwarding (RPF) information. As the name PIM implies,
it functions independently of the unicast protocols being used. PIM relies on
the Routing Information Base (RIB) for RPF information.
The Cisco IOS XR
implementation of PIM is based on RFC 4601 Protocol Independent Multicast -
Sparse Mode (PIM-SM): Protocol Specification. For more information, see RFC
4601 and the Protocol Independent Multicast (PIM): Motivation and Architecture
Internet Engineering Task Force (IETF) Internet draft.
Cisco IOS XR Software supports PIM-SM, PIM-SSM,
and PIM Version 2 only. PIM Version 1 hello messages that arrive
from neighbors are rejected.
Typically, PIM in sparse mode (PIM-SM) operation is used in a multicast network when relatively few routers are involved in each multicast. Routers do not forward multicast packets for a group, unless there is an explicit request for traffic. Requests are accomplished using PIM join messages, which are sent hop by hop toward the root node of the tree. The root node of a tree in PIM-SM is the rendezvous point (RP) in the case of a shared tree or the first-hop router that is directly connected to the multicast source in the case of a shortest path tree (SPT). The RP keeps track of multicast groups, and the sources that send multicast packets are registered with the RP by the first-hop router of the source.
As a PIM join travels up the tree, routers along the path set up the multicast forwarding state so that the requested multicast traffic is forwarded back down the tree. When multicast traffic is no longer needed, a router sends a PIM prune message up the tree toward the root node to prune (or remove) the unnecessary traffic. As this PIM prune travels hop by hop up the tree, each router updates its forwarding state appropriately. Ultimately, the forwarding state associated with a multicast group or source is removed. Additionally, if prunes are not explicitly sent, the PIM state will timeout and be removed in the absence of any further join messages.
PIM-SM is the best choice for multicast networks that have potential members at the end of WAN links.
PIM-Source Specific Multicast
In many multicast deployments where the source is known, protocol-independent multicast-source-specific multicast (PIM-SSM) mapping is the obvious multicast routing protocol choice to use because of its simplicity. Typical multicast deployments that benefit from PIM-SSM consist of entertainment-type solutions like the ETTH space, or financial deployments that completely rely on static forwarding.
PIM-SSM is derived from PIM-SM. However, whereas PIM-SM allows for the data transmission of all sources sending to a particular group in response to PIM join messages, the SSM feature forwards traffic to receivers only from those sources that the receivers have explicitly joined. Because PIM joins and prunes are sent directly towards the source sending traffic, an RP and shared trees are unnecessary and are disallowed. SSM is used to optimize bandwidth utilization and deny unwanted Internet broadcast traffic. The source is provided by interested receivers through IGMPv3 membership reports.
In SSM, delivery of datagrams is based on (S,G) channels. Traffic for one (S,G) channel consists of datagrams with an IP unicast source address S and the multicast group address G as the IP destination address. Systems receive traffic by becoming members of the (S,G) channel. Signaling is not required, but receivers must subscribe or unsubscribe to (S,G) channels to receive or not receive traffic from specific sources. Channel subscription signaling uses IGMP to include mode membership reports, which are supported only in Version 3 of IGMP (IGMPv3).
To run SSM with IGMPv3, SSM must be supported on the multicast router, the host where the application is running, and the application itself. Cisco IOS XR Software allows SSM configuration for an arbitrary subset of the IP multicast address range 18.104.22.168 through 22.214.171.124. When an SSM range is defined, existing IP multicast receiver applications do not receive any traffic when they try to use addresses in the SSM range, unless the application is modified to use explicit (S,G) channel subscription.
PIM Shared Tree and Source Tree (Shortest Path Tree)
In PIM-SM, the rendezvous point (RP) is used to bridge sources sending data to a particular group with receivers sending joins for that group. In the initial setup of state, interested receivers receive data from senders to the group across a single data distribution tree rooted at the RP. This type of distribution tree is called a shared tree or rendezvous point tree (RPT) as illustrated in Figure 1 . Data from senders is delivered to the RP for distribution to group members joined to the shared tree.
Figure 3. Shared Tree and Source Tree (Shortest Path Tree)
Unless the spt-threshold infinity command is configured, this
initial state gives way as soon as traffic is received on the leaf routers (designated
router closest to the host receivers). When the leaf router receives traffic from the RP on
the RPT, the router initiates a switch to a data distribution tree rooted at the source
sending traffic. This type of distribution tree is called a shortest path
tree or source tree. By default, the Cisco IOS XR Software switches to a source
tree when it receives the first data packet from a source.
The following process describes the move from shared tree to source tree in more detail:
Receiver joins a group; leaf Router C sends a join message toward RP.
RP puts link to Router C in its outgoing interface list.
Source sends data; Router A encapsulates data in Register and sends it to RP.
RP forwards data down the shared tree to Router C and sends a join message toward Source. At this point, data may arrive twice at the RP, once encapsulated and once natively.
When data arrives natively (unencapsulated) at RP, RP sends a register-stop message to Router A.
By default, receipt of the first data packet prompts Router C to send a join message toward Source.
When Router C receives data on (S,G), it sends a prune message for Source up the shared tree.
RP deletes the link to Router C from outgoing interface of (S,G). RP triggers a prune message toward Source.
Join and prune messages are sent for sources and RPs. They are sent hop by hop and are processed by each PIM router along the path to the source or RP. Register and register-stop messages are not sent hop by hop. They are exchanged using direct unicast communication between the designated router that is directly connected to a source and the RP for the group.
The spt-threshold infinity command lets you configure the
router so that it never switches to the shortest path tree (SPT).
The multicast-intact feature provides the ability to run multicast routing (PIM) when
Interior Gateway Protocol (IGP) shortcuts are configured and active on the router. Both
Open Shortest Path First, version 2 (OSPFv2), and Intermediate System-to-Intermediate
System (IS-IS) support the multicast-intact feature. Multiprotocol Label Switching Traffic
Engineering (MPLS-TE) and IP multicast coexistence is supported in Cisco IOS XR Software by using the
mpls traffic-eng multicast-intact IS-IS or OSPF router
Routing Configuration Guide for Cisco NCS 6000 Series
Routers for information on configuring multicast intact using IS-IS and OSPF commands.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGPs route the IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because reverse path forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set
of equal-cost next-hops for use by PIM. These next-hops are called mcast-intact
next-hops. The mcast-intact next-hops have the following attributes:
They are guaranteed not to contain any IGP shortcuts.
They are not used for unicast routing but are used only by PIM to look up an IPv4 next hop to a PIM source.
They are not published to the Forwarding Information Base (FIB).
When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute applies even when the native next-hops have no IGP shortcuts.
In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together. (In OSPFv2, the behavior is slightly different.)
Cisco routers use PIM-SM to forward multicast traffic and follow an election process to select a designated router (DR) when there is more than one router on a LAN segment.
The designated router is responsible for sending PIM register and PIM join and prune messages toward the RP to inform it about host group membership.
If there are multiple PIM-SM routers on a LAN, a designated router must be elected to avoid
duplicating multicast traffic for connected hosts. The PIM router with the highest IP
address becomes the DR for the LAN unless you choose to force the DR election by use of the
dr-priority command. The DR priority option allows you to
specify the DR priority of each router on the LAN segment (default priority = 1) so that
the router with the highest priority is elected as the DR. If all routers on the LAN
segment have the same priority, the highest IP address is again used as the tiebreaker.
Figure 1illustrates what happens on a multiaccess segment. Router A (10.0.0.253) and Router B (10.0.0.251) are connected to a common multiaccess Ethernet segment with Host A (10.0.0.1) as an active receiver for Group A. As the Explicit Join model is used, only Router A, operating as the DR, sends joins to the RP to construct the shared tree for Group A. If Router B were also permitted to send (*, G) joins to the RP, parallel paths would be created and Host A would receive duplicate multicast traffic. When Host A begins to source multicast traffic to the group, the DR’s responsibility is to send register messages to the RP. Again, if both routers were assigned the responsibility, the RP would receive duplicate multicast packets.
If the DR fails, the PIM-SM provides a way to detect the failure of Router A and to elect a failover DR. If the DR (Router A) were to become inoperable, Router B would detect this situation when its neighbor adjacency with Router A timed out. Because Router B has been hearing IGMP membership reports from Host A, it already has IGMP state for Group A on this interface and immediately sends a join to the RP when it becomes the new DR. This step reestablishes traffic flow down a new branch of the shared tree using Router B. Additionally, if Host A were sourcing traffic, Router B would initiate a new register process immediately after receiving the next multicast packet from Host A. This action would trigger the RP to join the SPT to Host A, using a new branch through Router B.
Figure 4. Designated Router Election on a Multiaccess Segment
Two PIM routers are neighbors if there is a direct connection between them. To display
your PIM neighbors, use the show
pim neighbor command in EXEC mode.
DR election process is required only on multiaccess LANs. The last-hop router directly connected to the host is the DR.
When PIM is configured in sparse mode, you must choose one or more routers to operate as a rendezvous point (RP). A rendezvous point is a single common root placed at a chosen point of a shared distribution tree, as illustrated in Figure 1. A rendezvous point can be either configured statically in each box or learned through a dynamic mechanism.
PIM DRs forward data from directly connected multicast sources to the rendezvous point for distribution down the shared tree. Data is forwarded to the rendezvous point in one of two ways:
Encapsulated in register packets and unicast directly to the rendezvous point by the first-hop router operating as the DR
Multicast forwarded by the RPF forwarding algorithm, described in the Reverse-Path Forwarding, if the rendezvous point has itself joined the source tree.
The rendezvous point address is used by first-hop routers to send PIM register messages on behalf of a host sending a packet to the group. The rendezvous point address is also used by last-hop routers to send PIM join and prune messages to the rendezvous point to inform it about group membership. You must configure the rendezvous point address on all routers (including the rendezvous point router).
A PIM router can be a rendezvous point for more than one group. Only one rendezvous point address can be used at a time within a PIM domain. The conditions specified by the access list determine for which groups the router is a rendezvous point.
You can either manually configure a PIM router to function as a rendezvous point or allow the rendezvous point to learn group-to-RP mappings automatically by configuring Auto-RP or BSR. (For more information, see the Auto-RP section that follows and PIM Bootstrap Router.)
processing (Auto-RP) is a feature that automates the distribution of
group-to-RP mappings in a PIM network. This feature has these benefits:
It is easy to use
multiple RPs within a network to serve different group ranges.
It allows load
splitting among different RPs.
It facilitates the
arrangement of RPs according to the location of group participants.
inconsistent, manual RP configurations that might cause connectivity problems.
Multiple RPs can be
used to serve different group ranges or to serve as hot backups for each other.
To ensure that Auto-RP functions, configure routers as candidate RPs so that
they can announce their interest in operating as an RP for certain group
ranges. Additionally, a router must be designated as an RP-mapping agent that
receives the RP-announcement messages from the candidate RPs, and arbitrates
conflicts. The RP-mapping agent sends the consistent group-to-RP mappings to
all remaining routers. Thus, all routers automatically determine which RP to
use for the groups they support.
By default, if a
given group address is covered by group-to-RP mappings from both static RP
configuration, and is discovered using Auto-RP or PIM BSR, the Auto-RP or PIM
BSR range is preferred. To override the default, and use only the RP mapping,
If you configure PIM
in sparse mode and do not configure Auto-RP, you must statically configure an
RP as described in the
Configuring a Static RP and Allowing Backward Compatibility. When router interfaces are
configured in sparse mode, Auto-RP can still be used if all routers are
configured with a static RP address for the Auto-RP groups.
PIM Bootstrap Router
The PIM bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution mechanism that simplifies the Auto-RP process. This feature is enabled by default allowing routers to dynamically learn the group-to-RP mappings.
PIM uses the BSR to discover and announce RP-set information for each group prefix to all the routers in a PIM domain. This is the same function accomplished by Auto-RP, but the BSR is part of the PIM Version 2 specification. The BSR mechanism interoperates with Auto-RP on Cisco routers.
To avoid a single point of failure, you can configure several candidate BSRs in a PIM domain. A BSR is elected among the candidate BSRs automatically. Candidates use bootstrap messages to discover which BSR has the highest priority. The candidate with the highest priority sends an announcement to all PIM routers in the PIM domain that it is the BSR.
Routers that are configured as candidate RPs unicast to the BSR the group range for which they are responsible. The BSR includes this information in its bootstrap messages and disseminates it to all PIM routers in the domain. Based on this information, all routers are able to map multicast groups to specific RPs. As long as a router is receiving the bootstrap message, it has a current RP map.
Reverse-path forwarding (RPF) is an algorithm used for forwarding multicast datagrams. It functions as follows:
If a router receives a datagram on an interface it uses to send unicast packets to the source, the packet has arrived on the RPF interface.
If the packet arrives on the RPF interface, a router forwards the packet out the interfaces present in the outgoing interface list of a multicast routing table entry.
If the packet does not arrive on the RPF interface, the packet is silently discarded to prevent loops.
PIM uses both source trees and RP-rooted shared trees to forward datagrams; the RPF check is performed differently for each, as follows:
If a PIM router has an (S,G) entry present in the multicast routing table (a source-tree state), the router performs the RPF check against the IP address of the source for the multicast packet.
If a PIM router has no explicit source-tree state, this is considered a shared-tree state. The router performs the RPF check on the address of the RP, which is known when members join the group.
Sparse-mode PIM uses the RPF lookup function to determine where it needs to send joins and prunes. (S,G) joins (which are source-tree states) are sent toward the source. (*,G) joins (which are shared-tree states) are sent toward the RP.
allows you to manipulate network traffic flow when desirable (for example, to
broadcast duplicate video streams) to flow over non-overlapping paths.
PIM uses a routing
policy that supports matching on source or group address to select the topology
in which to look up the reverse-path forwarding (RPF) path to the source. If
you do not configure a policy, the existing behavior (to select a default
table) remains in force.
Currently, IS-IS and
PIM routing protocols alone support multitopology-enabled network.
Multicast Source Discovery Protocol
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparse-mode domains. MSDP allows multicast sources for a group to be known to all rendezvous points (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains.
An RP in a PIM-SM domain has MSDP peering relationships with MSDP-enabled routers in other domains. Each peering relationship occurs over a TCP connection, which is maintained by the underlying routing system.
MSDP speakers exchange messages called Source Active (SA) messages. When an RP learns about a local active source, typically through a PIM register message, the MSDP process encapsulates the register in an SA message and forwards the information to its peers. The message contains the source and group information for the multicast flow, as well as any encapsulated data. If a neighboring RP has local joiners for the multicast group, the RP installs the S, G route, forwards the encapsulated data contained in the SA message, and sends PIM joins back towards the source. This process describes how a multicast path can be built between domains.
Although you should configure BGP or Multiprotocol BGP for optimal MSDP interdomain operation, this is not considered necessary in the Cisco IOS XR Software implementation. For information about how BGP or Multiprotocol BGP may be used with MSDP, see the MSDP RPF rules listed in the Multicast Source Discovery Protocol (MSDP), Internet Engineering Task Force (IETF) Internet draft.
Multicast Nonstop Forwarding
The Cisco IOS XR Software nonstop forwarding (NSF) feature for multicast enhances high availability (HA) of multicast packet forwarding. NSF prevents hardware or software failures on the control plane from disrupting the forwarding of existing packet flows through the router.
The contents of the Multicast Forwarding Information Base (MFIB) are frozen during a control plane failure. Subsequently, PIM attempts to recover normal protocol processing and state before the neighboring routers time out the PIM hello neighbor adjacency for the problematic router. This behavior prevents the NSF-capable router from being transferred to neighbors that will otherwise detect the failure through the timed-out adjacency. Routes in MFIB are marked as stale after entering NSF, and traffic continues to be forwarded (based on those routes) until NSF completion. On completion, MRIB notifies MFIB and MFIB performs a mark-and-sweep to synchronize MFIB with the current MRIB route information.
Cisco IOS XR Software moves control plane CLI configurations
to protocol-specific submodes to provide mechanisms for enabling, disabling,
and configuring multicast features on a large number of interfaces.
Cisco IOS XR Software allows you to issue most commands
available under submodes as one single command string from
For example, the
command could be executed from the multicast-routing
configuration submode like this:
RP/0/RP0/CPU0:router(config-mcast-ipv4)# ssm range
could issue the same command from
mode like this:
RP/0/RP0/CPU0:router(config)# multicast-routing ssm range
multicast protocol-specific submodes are available through these configuration
When you issue the
command, all default multicast components (PIM, IGMP,
, MFWD, and MRIB) are
automatically started, and the CLI prompt changes to “config-mcast-ipv4”
indicating that you have entered multicast-routing
When you issue the
command, the CLI prompt changes to “config-pim-ipv4,” indicating that you have
entered the default pim address-family configuration submode.
IGMP Configuration Submode
When you issue the router igmp command, the CLI prompt changes to
“config-igmp,” indicating that you have entered IGMP configuration submode.
MSDP Configuration Submode
When you issue the router msdp command, the CLI prompt changes to
“config-msdp,” indicating that you have entered router MSDP configuration submode.
Interface Configuration Inheritance
Cisco IOS XR Software allows you to configure commands for a
large number of interfaces by applying command configuration within a multicast
routing submode that could be inherited by all interfaces. To override the
inheritance mechanism, you can enter interface configuration submode and
explicitly enter a different command parameter.
For example, in the
following configuration you could quickly specify (under router PIM
configuration mode) that all existing and new PIM interfaces on your router
will use the hello interval parameter of 420 seconds. However,
Packet-over-SONET/SDH (POS) interface 0/1/0/1 overrides the global interface
configuration and uses the hello interval time of 210 seconds.
RP/0/RP0/CPU0:router(config)# router pim
RP/0/RP0/CPU0:router(config-pim-default-ipv4)# hello-interval 420
RP/0/RP0/CPU0:router(config-pim-default-ipv4)# interface pos 0/1/0/1
RP/0/RP0/CPU0:router(config-pim-ipv4-if)# hello-interval 210
Interface Configuration Inheritance Disablement
As stated elsewhere,
Cisco IOS XR Software allows you to configure multiple
interfaces by applying configurations within a multicast routing submode that
can be inherited by all interfaces.
To override the
inheritance feature on specific interfaces or on all interfaces, you can enter
the address-family IPv4
submode of multicast routing configuration mode, and enter the
disable command together with the
all command. This causes PIM or IGMP protocols to
disallow multicast routing and to allow only multicast forwarding on those
interfaces specified. However, routing can still be explicitly enabled on
specified individual interfaces.
Understanding Enabling and Disabling Interfaces
Enabling and Disabling Interfaces
Cisco IOS XR Software multicast routing feature is
configured on your router, by default, no interfaces are enabled.
To enable multicast
routing and protocols on a single interface or multiple interfaces, you must
explicitly enable interfaces using the
command in multicast routing configuration mode.
To set up multicast
routing on all interfaces, enter the
command in multicast routing configuration mode. For any interface to be fully
enabled for multicast routing, it must be enabled specifically (or be default)
in multicast routing configuration mode, and it must not be disabled in the PIM
For example, in the
following configuration, all interfaces are explicitly configured from
multicast routing configuration submode:
RP/0/RP0/CPU0:router(config-mcast)# interface all enable
To disable an
interface that was globally configured from the multicast routing configuration
submode, enter interface configuration submode, as illustrated in the following
RP/0/RP0/CPU0:router(config-mcast)# interface GigabitEthernet0pos 0/1/0/0
The Multicast Routing
Information Base (MRIB) is a protocol-independent multicast routing table that
describes a logical network in which one or more multicast routing protocols
are running. The tables contain generic multicast routes installed by
individual multicast routing protocols. There is an MRIB for every logical
network in which the router is configured. MRIBs do not redistribute routes
among multicast routing protocols; they select the preferred multicast route
from comparable ones, and they notify their clients of changes in selected
attributes of any multicast route.
Information Base (MFIB) is a protocol-independent multicast forwarding system
that contains unique multicast forwarding entries for each source or group pair
known in a given network. There is a separate MFIB for every logical network in which
the router is configured. Each MFIB entry resolves a given source or group pair
to an incoming interface (IIF) for reverse forwarding (RPF) checking and an
outgoing interface list (olist) for multicast forwarding.
MSDP MD5 Password Authentication
MSDP MD5 password authentication is an enhancement to support Message Digest 5 (MD5) signature protection on a TCP connection between two Multicast Source Discovery Protocol (MSDP) peers. This feature provides added security by protecting MSDP against the threat of spoofed TCP segments being introduced into the TCP connection stream.
MSDP MD5 password authentication verifies each segment sent on the TCP connection between
MSDP peers. The password clear command is used to enable MD5
authentication for TCP connections between two MSDP peers. When MD5 authentication is
enabled between two MSDP peers, each segment sent on the TCP connection between the peers
MSDP MD5 authentication must be configured with the same password on both MSDP peers to enable the connection between them. The 'password encrypted' command is used only for applying the stored running configuration. Once you configure the MSDP MD5 authentication, you can restore the configuration using this command.
MSDP MD5 password authentication uses an industry-standard MD5 algorithm for improved reliability and security.
Policy for Static RPF
| ||Command or Action||Purpose|
RP/0/RP0/CPU0:router(config) # router static
Enables a static
RP/0/RP0/CPU0:router(config-static) # address-family ipv4 multicast 126.96.36.199/ 32 188.8.131.52
ipv4 multicast address-family topology with a destination prefix.
RP/0/RP0/CPU0:router(config-ipv4-afi) # exit
Exits from the
address family configuration mode.
RP/0/RP0/CPU0:router(config) # route-policy r1
route policy to select the RPF topology.
RP/0/RP0/CPU0:router(config-rpl) # set rpf-topology p1 ipv4 multicast topology t1
PIM rpf-topology attributes for the selected multicast address-family.
RP/0/RP0/CPU0:router(config-rpl) # end route-policy r1
Ends the route
RP/0/RP0/CPU0:router(config) # router pim address-family ipv4
Enters the PIM
address-family configuration sub-mode.
RP/0/RP0/CPU0:router(config) # rpf topology route-policy r1 pim policy
RPF topology for the configured route-policy.
Configuration Examples for Implementing Multicast Routing on Software
This section provides the following configuration examples:
Preventing Auto-RP Messages from Being Forwarded on Software: Example
This example shows that Auto-RP messages are prevented from being sent out of the
interface 0/3/0/0. It also shows that access list 111 is used by the Auto-RP
candidate and access list 222 is used by the boundary command
to contain traffic on
ipv4 access-list 111
10 permit 184.108.40.206 0.0.255.255 any
20 permit 220.127.116.11 0.0.255.255 any
!Access list 111 is used by the Auto-RP candidate.
ipv4 access-list 222
10 deny any host 18.104.22.168
20 deny any host 22.214.171.124
!Access list 222 is used by the boundary command to contain traffic (on /3/0/0) that is sent to groups 126.96.36.199 and 188.8.131.52.
auto-rp mapping-agent loopback 2 scope 32 interval 30
auto-rp candidate-rp loopback 2 scope 15 group-list 111 interval 30
Inheritance in MSDP on Software: Example
The following MSDP commands can be inherited by all MSDP peers when configured under router MSDP configuration mode. In addition, commands can be configured under the peer configuration mode for specific peers to override the inheritance feature.
If a command is configured in both the router msdp and peer configuration modes, the peer configuration takes precedence.
In the following example, MSDP on Router A filters Source-Active (SA) announcements on all peer groups in the address range 226/8 (except IP address 172.16.0.2); and filters SAs sourced by the originator RP 172.16.0.3 to 172.16.0.2.
MSDP peers (172.16.0.1, 172.16.0.2, and 172.17.0.1) use the loopback 0 address of Router A to set up peering. However, peer 192.168.12.2 uses the IPv4 address configured on the
interface to peer with Router A.
ipv4 access-list 111
10 deny ip host 172.16.0.3 any
20 permit any any
ipv4 access-list 112
10 deny any 184.108.40.206 0.255.255.255
30 permit any any
connect-source loopback 0
sa-filter in rp-list 111
sa-filter out rp-list 111
sa-filter out list 112
Configuring Route Policy for Static RPF: Example
address-family ipv4 multicast
220.127.116.11 /32 18.104.22.168
set rpf-topology ipv4 multicast topology default
rpf topology route-policy pim-policy
Multicast command reference document
Multicast Command Reference for Cisco NCS 6000 Series
Getting started material
Modular quality of service command reference document
Routing command reference and configuration documents
Routing Command Reference for
Cisco NCS 6000 Series Routers
Routing Configuration Guide for Cisco NCS 6000 Series
Information about user groups and task IDs
System Security Configuration Guide for Cisco NCS 6000 Series