L2VPN Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Split-horizon groups

Updated: June 15, 2026

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Introduces split-horizon group concepts, listing supported group types and providing configuration steps to prevent packet looping within VPLS bridge domains.

A split-horizon group is a bridge-domain grouping that

  • prevents loops by applying forwarding and flooding restrictions between bridge ports based on group membership

  • restricts traffic between members of the same group, and

  • still allows traffic between different groups.

Table 1. Feature history table

Feature Name

Release Information

Feature Description

Split-Horizon Groups

Release 25.4.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is supported on:

  • 8011-12G12X4Y-A

  • 8011-12G12X4Y-D

Split-Horizon Groups

Release 25.1.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is supported on Cisco 8011-4G24Y4H-I routers.

Split-Horizon Groups

Release 24.4.1

Introduced in this release on: Fixed Systems (8700) (select variants only*)

* The split-horizon groups functionality is now extended to the Cisco 8712-MOD-M routers.

Split-Horizon Groups

Release 24.3.1

Introduced in this release on: Fixed Systems (8200 [ASIC: Q200, P100], 8700 [ASIC: P100])(select variants only*); Modular Systems (8800 [LC ASIC: Q100, Q200, P100])(select variants only*)

*The split-horizon groups functionality is now extended to:

  • 8212-48FH-M

  • 8711-32FH-M

  • 88-LC1-52Y8H-EM

  • 88-LC1-12TH24FH-E

Split-Horizon Groups

Release 24.2.11

Introduced in this release on: Modular Systems (8800 [LC ASIC: P100]) (select variants only*)

*The split-horizon groups functionality is now extended to routers with the 88-LC1-36EH line cards.

Split-Horizon Groups

 Release 7.3.2

This feature prevents packets from going into endless loops by aggregating attachment circuits and pseudowires into one of three groups called split-horizon groups. Split-horizon groups operate on the principle that members within a group will not send traffic to each other thereby preventing traffic loops.

Supported split-horizon groups

Bridge domains use three split-horizon groups, each with distinct forwarding and flooding behavior. Traffic flooding applies to broadcast, multicast, and unknown unicast destination addresses. Unicast traffic consists of frames sent to bridge-ports where the destination MAC address is known.

Flooding traffic consists of:

  • Unknown unicast destination MAC address frames

  • Frames sent to Ethernet multicast addresses such as Spanning Tree BPDUs

  • Ethernet broadcast frames with MAC address FF-FF-FF-FF-FF-FF

Bridge domain traffic is either unicast or flooding. Members within certain groups are forbidden to send traffic to each other, while members in different groups can send traffic to each other without restriction.

Table 2. Supported split-horizon groups

Split-Horizon Group

Behavior

0

Default AC group. There is no forwarding and flooding restrictions. Forwards and floods traffic within the group and between all groups. By default, all L2 ACs are added to this group and you cannot assign them manually through the CLI.

1

Default VFI core PW group. Forwarding or flooding of traffic is restricted between bridge ports in this group. Traffic to all other groups is allowed. All VFI pseudowires are added to this group and you cannot assign them manually through the CLI.

2

Optional AC group. Forwarding or flooding of traffic is restricted between bridge ports in this group. Traffic to all other groups is allowed. You can manually add ACs, and not VFI pseudowires, by using the CLI.

Configure split-horizon groups

Assign split-horizon groups to ACs and pseudowires within a bridge domain to optimize traffic management and prevent unwanted loopbacks.

The bridge domain aggregates attachment circuits and pseudowires into one of three split-horizon groups, separating traffic and enhancing network stability.

Before you begin

Follow these steps to configure the split-horizon groups:

Procedure

1.

Configure split-horizon groups on the attachment circuits and pseudowire.

Example:

Router# configure
Router(config)# l2vpn
Router(config-l2vpn)# bridge group bg
Router(config-l2vpn-bg)# bridge-domain bd
Router(config-l2vpn-bg-bd-ac)# interface Ten0/7/0/22/0
Router(config-l2vpn-bg-bd-ac)# interface Ten0/7/0/22/1.1
Router(config-l2vpn-bg-bd-ac)# split-horizon group
Router(config-l2vpn-bg-bd-ac)# neighbor 10.0.0.1 pw-id 1
Router(config-l2vpn-bg-bd-pw)# split-horizon group
Router(config-l2vpn-bg-bd-pw)# vfi vf
Router(config-l2vpn-bg-bd-vfi)# neighbor 172.16.0.1 pw-id 10001
Router(config-l2vpn-bg-bd-vfi-pw)# commit
2.

Review the running configuration.

Example:

l2vpn
  bridge group bg
   bridge-domain bd
    int Ten0/7/0/22/0
    int Ten0/7/0/22/1.1
     split-horizon group
    neighbor 10.0.0.1 pw-id 1
     split-horizon group
    vfi vf
      neighbor 172.16.0.1 pw-id 10001
!
3.

Use the show l2vpn bridge-domain detail | i "AC:|Split Horizon|PW:|VFI command to verify the split-horizon group assignments.

Example:

Router# show l2vpn bridge-domain detail | i "AC:|Split Horizon|PW:|VFI"
MAC withdraw for Access PW: enabled
Split Horizon Group: none
AC: Ten0/7/0/22/0, state is up
Split Horizon Group: none
AC: Ten0/7/0/22/1, state is up
Split Horizon Group: enabled
PW: neighbor 10.0.0.1, pw-id 1, state is up ( established )
Split Horizon Group: enabled
VFI vf (up)
PW: neighbor 172.16.0.1, pw-id 10001, state is up ( established )
Split Horizon Group: none

The bridge-domain ACs and pseudowires are successfully assigned to the intended split-horizon groups, optimizing network traffic and preventing unwanted loopbacks.