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Multicast only Fast Re-Route (MoFRR) is an IP solution that minimizes packet loss in a network when there is a link or node
failure. It works by making simple enhancements to multicast routing protocols like Protocol Independent Multicast (PIM).
MoFRR transmits a multicast join message from a receiver toward a source on a primary path, while also transmitting a secondary
multicast join message from the receiver toward the source on a backup path. Data packets are received from both the primary
path and the secondary paths. The redundant packets are discarded at topology merge points due to Reverse Path Forwarding
(RPF) checks. When a failure is detected on the primary path, the repair is made by changing the interface on which packets
are accepted to the secondary interface.Because the repair is local, it is fast--greatly improving convergence times in the
event of node or link failures on the primary path.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module,
and to see a list of the releases in which each feature is supported, see the feature information table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for MoFRR
Before performing the tasks in this module, you should be familiar with the concepts described in “ IP Multicast Technology
Overview ” module.
The tasks in this module assume that IP multicasting has been enabled and that PIM interfaces have been configured using
the tasks described in the “ Configuring Basic IP Multicast ” module.
Restrictions for MoFRR
The MoFRR feature is disabled by default and must be enabled using the CLI.
The Equal Cost Multipath Protocol (ECMP) feature is a requirement in order for the MoFRR feature to function.
MoFRR works only for Specific Multicast (SM) S, G, and Source Specific Multicast (SSM) routes.
MoFRR is applicable to only IPv4 Multicast, not IPv6 Multicast.
MoFRR does not support extranet routes.
MoFRR works where the Reverse Path Forwarding (RPF) lookups are done in a single VRF.
Both primary and secondary paths should exist in the same multicast topology.
MoFRR is supported on images supporting IPv4 MFIB only.
Information About MoFRR
Overview of MoFRR
The MoFRR feature provides the ability to minimize packet loss in a network when there is a link or node failure by enhancing,
but not changing, multicast routing protocols such as PIM. With MoFRR, multicast routing protocols do not have to wait or
depend on unicast routing protocols to detect network failures.
The MoFRR feature can be divided into two planes, red and blue, that are fully disjoint from each other all the way into
the points of presence (POPs) as shown in the figure.
This two-plane design eliminates single points of failure in the core network. The upstream full-line arrows indicate the
normal path taken when the PIM joins the flow from the POPs toward the source of the network.
MoFRR adds the broken-arrow path where the provider edge (PE) routers send an alternate PIM join to their neighbor toward
the source. Each PE router then receives two copies of the same stream, one from the blue plane and one from the red plane.
As a result of multicast RPF checks, the following occurs:
The multicast stream received over the primary path (in the reverse direction of the full-line arrows) is accepted and forwarded
to the downstream links.
The copy of the stream received on the alternate path (in the reverse direction of the broken-line arrows) is discarded
When a routing failure occurs, for example due to a link failure in the blue path, the red upstream router in the red plane
becomes the primary upstream router to reach the source. This link to the router then becomes the RPF interface, and the copy
of the multicast stream being received on the link is accepted and forwarded to the downstream links.
MoFRR achieves faster convergence by prebuilding the alternate multicast tree and receiving the traffic on that alternate
path. The example discussed above is a simple case where there are two paths from each PE device toward the source, one along
the blue plane and one along the red plane. MoFRR switchover as a result of routing convergence is expected to be in the order
of -200 milliseconds.
How to Configure MoFRR
Enabling MoFRR
Perform this task to configure MoFRR.
Multiple ACL configurations are not allowed. Multicast routes are enabled for MoFRR based on the first match in the ACL.
SUMMARY STEPS
enable
configure terminal
ip multicast-routing [vrf vrf-name] [distributed]
interface type number [name-tag]
ip address ip-addressmask [secondary [vrf vrf-name]]
Displays the contents of the multicast routing (mroute) table.
Note
The MoFRR keyword will be displayed in the command output for MoFRR-enabled routes.
Configuration Examples for MoFRR
Example Enabling MoFRR
This example shows MoFRR being enabled for the S, G matching ACL 125.
Device> enable
Device# configure terminal
Device(config)# ip multicast-routing vrf2
Device(config)# interface fastethernet 0/0
Device(config-if)# ip address 209.165.200.225 0.0.0.0
Device(config-if)# ip pim sparse-dense-mode
Device(config-if)# exit
Device(config)# ip multicast rpf mofrr 125
Device(config)# ip access-list extended 125Device(config-ext-nacl)# permit 209.165.201.1 255.255.255.224Device(config-ext-nacl)# end
Example Verifying That MoFRR Is Enabled
The smaple output in the following example shows that MoFRR is enabled for the 209.165.200.225 multicast source IP address.
The relevant command output is shown in bold.
device> enable
Device# show ip rpf 209.165.200.225
RPF information for ? (209.165.200.225) MoFRR Enabled
RPF interface: Ethernet1/4
RPF neighbor: ? (209.165.201.1)
RPF route/mask: 255.255.255.224
RPF type: unicast (ospf 200)
Doing distance-preferred lookups across tables
RPF topology: ipv4 multicast base, originated from ipv4 unicast base
Secondary RPF interface: Ethernet1/3
Secondary RPF neighbor: ? (209.165.202.129)
For a detailed explanation of the output, see the
show ip rpf command in the
Cisco Ip Multicast Command Reference.
IP multicast commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples
Cisco IOS IP Multicast Command Reference
Overview of the IP multicast technology area
IP Multicast Technology Overview module
Concepts, tasks, and examples for configuring an IP multicast network using PIM
Configuring a Basic IP Multicast module
Standards
Standard
Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this
feature.
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MIBs
MIB
MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.
--
RFCs
RFC
Title
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
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Technical Assistance
Description
Link
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use
these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products
and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for MoFRR
Feature Name
Releases
Feature Information
MoFRR
Cisco IOS XE Release 3.2S
15.2(3)T
15.1(2)SY
The MoFRR feature provides the ability to minimize packet loss in a network when there is a link or node failure by enhancing,
but not changing, multicast routing protocols such as PIM. With MoFRR, multicast routing protocols do not have to wait or
depend on unicast routing protocols to detect network failures.
The following commands were introduced or modified:
ip access-list, ip multicast rpf mofrr, ip multicast-routing, permit (IP), show ip mroute, show ip rpf .
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