Configure Anycast RP Using MSDP for NX-OS

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Updated:May 2, 2024
Document ID:221962

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    Introduction

    This document describes how to configure Anycast RP using MSDP on a Nexus switch running in NX-OS mode.

    Prerequisites

    Requirements

    It is recommended that you have knowledge of these topics:

    Components Used

    The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

    The information in this document is based on Cisco Nexus 9000 with NXOS version 9.3.9.

    Background Information

    Although the protocol Anycast-RP is more commonly used to share the role of RP between two or more PIM routers in the same routing domain, MSDP can also be used.

    Configure

    Network Diagram

    Network Diagram

     

    Note: In the previous diagram, the blue links are labeled as Layer 2 Interface and the red links are labeled as Layer 3 Interface.

    Configure  Unicast and Multicast before MSDP

    Before MSDP can be configured, unicast and multicast must be configured on all the layer 3 Nexus switches including the RPs. In this example, EIGRP was configured on all Layer 3 interfaces and ICMP pings were successful from source to receiver.

    IGMP is configured on layer 3 interfaces by default. However, you must enable PIM on the layer 3 interfaces as well as statically configure the rp-address that you plan to use on RP-1 and RP-2:

    FHR-1:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface Vlan87
  ip pim sparse-mode

interface Ethernet1/7
  ip pim sparse-mode

interface Ethernet1/9
  ip pim sparse-mode
    FHR-2:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface Vlan87
  ip pim sparse-mode

interface Ethernet1/7
  ip pim sparse-mode

interface Ethernet1/9
  ip pim sparse-mode
    RP-1:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface loopback0
  ip pim sparse-mode

interface Ethernet1/53
  ip pim sparse-mode

interface Ethernet1/54
  ip pim sparse-mode
    RP-2:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface loopback0
  ip pim sparse-mode

interface Ethernet1/53
  ip pim sparse-mode

interface Ethernet1/54
  ip pim sparse-mode
    LHR-1:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface Vlan5
  ip pim sparse-mode

interface Ethernet1/53
  ip pim sparse-mode

interface Ethernet1/54
  ip pim sparse-mode
    LHR-2:
feature pim

ip pim rp-address 10.1.1.1 group-list 224.0.0.0/4

interface Vlan5
  ip pim sparse-mode

interface Ethernet1/53
  ip pim sparse-mode

interface Ethernet1/54
  ip pim sparse-mode

    Configure  MSDP Peering on all RPs in the Network

    Each Nexus switch that is a member of the Anycast RP set must be configured to peer with all other Nexus switches. In this example, RP-1 and RP-2 are both configured as peers:

    RP-1:
    feature msdp

    ip msdp originator-id loopback1
    ip msdp peer 10.1.1.3 connect-source loopback1
    ip msdp mesh-group 10.1.1.3 rp-mesh

    interface loopback0
      description Anycast RP Address
  ip address 10.1.1.1/32
  ip router eigrp 1
  ip pim sparse-mode

interface loopback1
      description MSDP Originator ID
  ip address 10.1.1.2/32
  ip router eigrp 1
    RP-2:
    feature msdp

    ip msdp originator-id loopback1
    ip msdp peer 10.1.1.2 connect-source loopback1
    ip msdp mesh-group 10.1.1.2 rp-mesh

    interface loopback0
      description Anycast RP Address 
      ip address 10.1.1.1/32
      ip router eigrp 1
      ip pim sparse-mode

    interface loopback1
      description MSDP Originator ID
      ip address 10.1.1.3/32
      ip router eigrp 1

    Note: In this example, interface loopback1 is used for MSDP peering and not PIM. For that reason, ip pim sparse-mode does not need to be configured on interface loopback1. That said, there is no harm in enabling PIM sparse-mode on interface loopback1.

    Verify

    MSDP peering is configured correctly when you see the Connection State is Established. You can see the counter for (S,G)s Received increase:

    RP-1# show ip msdp summary 
    MSDP Peer Status Summary for VRF "default"
    Local ASN: 0, originator-id: 10.1.1.2

    Number of configured peers:  1
    Number of established peers: 1
    Number of shutdown peers:    0

    Peer            Peer        Connection      Uptime/   Last msg  (S,G)s
    Address         ASN         State           Downtime  Received  Received
    10.1.1.3        0           Established     01:33:54  never     1

    Note: The counter for (S,G)s Received remains at 0 if there is no multicast in the network.

    Troubleshoot

    MSDP Peering Stuck in Listening State

    The show ip msdp summary command indicates that Connection State is in the Listening state:

    RP-1# show ip msdp summary 
    MSDP Peer Status Summary for VRF "default"
    Local ASN: 0, originator-id: 10.1.1.2

    Number of configured peers:  1
    Number of established peers: 0
    Number of shutdown peers:    0

    Peer            Peer        Connection      Uptime/   Last msg  (S,G)s
    Address         ASN         State           Downtime  Received  Received
    10.1.1.3        0           Listening       00:03:27  never     0

    The likely causes for this issue are:

    1. MSDP is incorrectly configured.
    2. A connectivity failure caused the MSDP peers to be unable to reach each other.

    In this example, assuming the configuration is correct, ethanalyzer can be used to troubleshoot potential packet loss between 10.1.1.2 and 10.1.1.3.

    Note: Watch How to perform Ethanalyzer captures on Nexus series switches for more details about ethanalyzer.

    Multicast (S, G)s not Shared

    If the Connection State is Established but (S,G)s Received is not incrementing, it is likely that MSDP is not configured properly. The most likely cause for this behavior is that the (S,G)s are being discarded due to a detected duplicate rp-address:

    RP-1# show ip msdp event-history events | i looping
    2023 Sep 22 12:13:15.106735 msdp [26860]: : Possible looping SA or duplicate RP address exists, RP 10.1.1.1, entry count: 1, length 20, message discarded
2023 Sep 22 12:10:10.314695 msdp [26860]: : Possible looping SA or duplicate RP address exists, RP 10.1.1.1, entry count: 1, length 20, message discarded
    2023 Sep 22 12:09:08.352690 msdp [26860]: : Possible looping SA or duplicate RP address exists, RP 10.1.1.1, entry count: 1, length 20, message discarded
    2023 Sep 22 12:08:06.688953 msdp [26860]: : Possible looping SA or duplicate RP address exists, RP 10.1.1.1, entry count: 1, length 20, message discarded
    2023 Sep 22 12:07:04.403736 msdp [26860]: : Possible looping SA or duplicate RP address exists, RP 10.1.1.1, entry count: 1, length 20, message discarded

    By default, the Nexus switch is configured to use the rp-address as the originator-id. However, that causes each MSDP peer to use the same originator-id which causes the (S,G)s to be discarded.

    In this example, if the originator-id is not configured, the rp-address 10.1.1.1 from loopback0 is used as the originator-id when it must be a unique IP for Anycast RP to work:

    RP-1:
    feature msdp

    ip msdp peer 10.1.1.3 connect-source loopback1
    ip msdp mesh-group 10.1.1.3 rp-mesh

    interface loopback0
    description Anycast RP Address
    ip address 10.1.1.1/32
    ip router eigrp 1
    ip pim sparse-mode

    interface loopback1
    description MSDP Originator ID
    ip address 10.1.1.2/32
    ip router eigrp 1
    RP-2:
    feature msdp

    ip msdp peer 10.1.1.2 connect-source loopback1
    ip msdp mesh-group 10.1.1.2 rp-mesh

    interface loopback0
    description Anycast RP Address
    ip address 10.1.1.1/32
    ip router eigrp 1
    ip pim sparse-mode

    interface loopback1
    description MSDP Originator ID
    ip address 10.1.1.3/32
    ip router eigrp

    The originator-id is confirmed in the MSDP summary show command:

    RP-1# show ip msdp summary 
    MSDP Peer Status Summary for VRF "default"
    Local ASN: 0, originator-id: 10.1.1.1 <--- rp-address from loopback0 is used for the originator-id

    Number of configured peers:  1
    Number of established peers: 0
    Number of shutdown peers:    0

    Peer            Peer        Connection      Uptime/   Last msg  (S,G)s
    Address         ASN         State           Downtime  Received  Received
    10.1.1.3        0           Established     01:33:54  never     0
    RP-2# show ip msdp summary 
    MSDP Peer Status Summary for VRF "default"
    Local ASN: 0, originator-id: 10.1.1.1 <--- rp-address from loopback0 is used for the originator-id

    Number of configured peers:  1
    Number of established peers: 0
    Number of shutdown peers:    0

    Peer            Peer        Connection      Uptime/   Last msg  (S,G)s
    Address         ASN         State           Downtime  Received  Received
    10.1.1.2        0           Established     01:33:54  never     0

    Note: If MSDP is used to peer between BGP Autonomous Systems (AS)s where the rp-address is typically different, the originator-id can be left default. However, if MSDP is used for Anycast RP, the originator-id must be unique on each MSDP peer.

    To resolve this issue, ip msdp originator-id loopback1 must be configured on both of the MSDP peers to ensure that a unique originator-id is used.

    Related Information

    Revision History

    Revision Publish Date Comments
    2.0
    02-May-2024
    Initial Release
    1.0
    02-May-2024
    Initial Release
    TAC Authored

    Contributed by Cisco Engineers

    • Jordan Andrews
      Cisco TAC Engineer

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