IP Multicast: Multicast Services Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
Multicast only Fast Re-Route
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Multicast only Fast Re-Route

Multicast only Fast Re-Route

Last Updated: August 27, 2012

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 at the end of this module.

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

1.    enable

2.    configure terminal

3.    ip multicast-routing [vrf vrf-name] [distributed]

4.    interface type number [name-tag]

5.    ip address ip-address mask [secondary [vrf vrf-name]]

6.    ip pim {dense-mode[proxy-register{list access-list | route-map map-name}] | passive | sparse-mode | sparse-dense-mode}

7.    exit

8.    Repeat Steps 4 through 7 for each interface to be configured.

9.    ip multicast [vrf vrf-name] rpf mofrr {access-list-number | access-list-name} [sticky]

10.    ip access-list { standard | extended } { access-list-name | access-list-number }

11.    [sequence-number] permit source [source-wildcard[

12.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
ip multicast-routing [vrf vrf-name] [distributed]


Example:

Device(config)# ip multicast-routing vrf vrf1

 

Enables multicast routing. Depending on your release, the distributed keyword may not be supported for this command.

  • In this example, multicast routing is enabled on a vrf instance named vrf1.
 
Step 4
interface type number [name-tag]


Example:

Device(config)# interface loopback 4

 

Selects an interface that is connected to hosts on which PIM can be enabled.

  • In this example, loopback interface 4 is selected.
 
Step 5
ip address ip-address mask [secondary [vrf vrf-name]]


Example:

Device(config-if)# ip address 209.165.200.225 255.255.255.224

 

Sets a primary or secondary IP address for the interface.

  • In this example, 209.165.200.225 is set as the primary address for loopback interface 4.
 
Step 6
ip pim {dense-mode[proxy-register{list access-list | route-map map-name}] | passive | sparse-mode | sparse-dense-mode}


Example:

Device(config-if)# ip pim sparse-dense-mode

 

Enables PIM sparse-dense mode on an interface.

 
Step 7
exit


Example:

Device(config-if)# exit

 

Exits interface configuration mode and returns to global configuration mode.

 
Step 8
Repeat Steps 4 through 7 for each interface to be configured.
 

--

 
Step 9
ip multicast [vrf vrf-name] rpf mofrr {access-list-number | access-list-name} [sticky]


Example:

Device(config)# ip multicast rpf mofrr 150

 

Enables MoFRR for a multicast routing entry that is specific to a source and a group (S, G) matching the ACL.

  • In this example, MoFRR is enabled for the S, G matching the ACL numbered 150.
 
Step 10
ip access-list { standard | extended } { access-list-name | access-list-number }


Example:

Device(config)# ip access-list extended 150

 

Defines a standard or extended IP access list or object group access control list (OGACL) by name or number.

  • In this example, an ACL numbered 150 is defined.
Note    MoFRR accepts extended ACLs only. It does not accept standard ACLs.
 
Step 11
[sequence-number] permit source [source-wildcard[


Example:

Device(config-ext-nacl)# permit 192.168.34.0 0.0.0.255

 

Sets conditions to allow a packet to pass a numbered IP access list.

  • In this example, packets from source address 192.168.34.0 are allowed to pass the ACL.
 
Step 12
end


Example:

Device(config-ext-nacl)# end

 

Exits standard named access list configuration mode and returns to privileged EXEC mode.

 

Verifying That MoFRR Is Enabled

Perform these steps to verify the configuration of MoFRR.

SUMMARY STEPS

1.    enable

2.    show ip rpf [vrf vrf-name ] source-address [group-address] [rd route-distinguisher]} [metric]

3.    show ip mroute [vrf vrf-name] [[active [kbps] [interface type number] | bidirectional | count [terse] | dense | interface type number | proxy | pruned | sparse | ssm | static | summary] | [group-address [source-address]] [count [terse] | interface type number | proxy | pruned | summary] | [source-address group-address] [count [terse] | interface type number | proxy | pruned | summary] | [group-address] active [kbps] [interface type number | verbose]]


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show ip rpf [vrf vrf-name ] source-address [group-address] [rd route-distinguisher]} [metric]


Example:

Device# show ip rpf 10.1.1.100

 

Displays the information that IP multicast routing uses to perform the Reverse Path Forwarding (RPF) check for a multicast source.

Note    The MoFRR keyword will be displayed in the command output for MoFRR-enabled routes.
 
Step 3
show ip mroute [vrf vrf-name] [[active [kbps] [interface type number] | bidirectional | count [terse] | dense | interface type number | proxy | pruned | sparse | ssm | static | summary] | [group-address [source-address]] [count [terse] | interface type number | proxy | pruned | summary] | [source-address group-address] [count [terse] | interface type number | proxy | pruned | summary] | [group-address] active [kbps] [interface type number | verbose]]


Example:

Device# show ip mroute

 

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 125
Device(config-ext-nacl)# permit 209.165.201.1 255.255.255.224
Device(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.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

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.

--

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.

--

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.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for MoFRR

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

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 .

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.