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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.
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.
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:
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.
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.
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
Perform these steps to verify the configuration of MoFRR.
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]]
Command or Action | Purpose | |||
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Step 1 | enable Example: Device> enable |
Enables privileged EXEC mode. |
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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.
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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.
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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
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.
Related Topic |
Document Title |
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Cisco IOS commands |
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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 |
Standard |
Title |
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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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MIB |
MIBs Link |
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No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
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RFC |
Title |
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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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Description |
Link |
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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.
Feature Name |
Releases |
Feature Information |
---|---|---|
MoFRR |
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 . |