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

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256-way multipath ECMP

Updated: February 28, 2026

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Overview

Describes the support for up to 256 ECMP next hops in BGP for IPv4 and IPv6, optimizing bandwidth by load balancing traffic across parallel paths with associated restrictions.

256-way multipath ECMP is a BGP feature that

  • enables configuration of up to 256 next hops for ECMP in BGP in both IPv4 and IPv6, and

  • optimizes network bandwidth by load balancing traffic across parallel paths.

Equal-cost multipath routing (ECMP) is a network technique that allows data packets destined for a single location to be sent via several optimal routes. These routes are considered equally efficient based on routing criteria. This approach works with most network protocols because each router independently determines the best forwarding path. ECMP can enhance network capacity by distributing data flow across diverse routes. With the 256-path ECMP capability, a router can use up to 256 simultaneous connections to reach a given endpoint.

Cisco 8000 Series Routers allow configuration of up to 256 ECMP next hops for BGP in both IPv4 and IPv6. This maximum 256-path ECMP capability extends to the global BGP table, particularly for iBGP and eBGP prefixes.

Table 1. Feature History Table

Feature Name

Release Name

Description

256-way ECMP

Release 25.4.1

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

*This feature is now supported on:

  • 8011-32Y8L2H2FH

  • 8011-12G12X4Y-A

  • 8011-12G12X4Y-D

256-way ECMP

Release 25.1.1

Introduced in this release on: Fixed Systems (8700 [ASIC: K100], 8010 [ASIC: A100])(select variants only*)

*This feature is supported on:

  • 8712-MOD-M

  • 8011-4G24Y4H-I

256-way ECMP

Release 24.4.1

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

You can now configure up to 256 ECMP next hops for BGP in both IPv4 and IPv6. This optimizes network bandwidth by load balancing traffic across parallel paths.

*This feature is supported on:

  • 8212-48FH-M

  • 8711-32FH-M

  • 88-LC1-36EH

  • 88-LC1-12TH24FH-E

  • 88-LC1-52Y8H-EM

Restrictions for 256-way multipath ECMP

These restrictions apply to the 256-way multipath ECMP feature:

  • BGP and IGP in UCMP support 256 path ECMP for IP, and 64 path ECMP for MPLS.

  • LDP receives only 64 ECMP support from the RIB. As a result, LSD receives a maximum of 64 ECMPs from all clients.

Configure 256-way multipath ECMP

Configure 256-way multipath ECMP for iBGP, eBGP, or eiBGP to enable traffic load balancing across multiple paths.

You can configure eBGP and iBGP multipath to function together. However, if eiBGP multipath is already configured, you cannot configure iBGP or eBGP multipath.

Procedure

1.

Configure 256-multipath ECMP for the desired BGP type, iBGP, eBGP, or eiBGP.

  1. Configure 256-multipath ECMP in iBGP.

    Example:

    
Router(config)#router bgp 100
Router(config-bgp)#bgp router-id 10.10.10.11
Router(config-bgp)#address-family ipv4 unicast
Router(config-bgp-af)#maximum-paths ibgp 256
Router(config-bgp-af)#exit
Router(config-bgp)#address-family ipv6 unicast
Router(config-bgp-af)#maximum-paths ibgp 256
Router(config-bgp-af)#commit

  2. Configure 256-multipath ECMP in eBGP.

    Example:

    
Router(config)#router bgp 100
Router(config-bgp)#bgp router-id 10.10.10.11
Router(config-bgp)#address-family ipv4 unicast
Router(config-bgp-af)#maximum-paths ebgp 256
Router(config-bgp-af)#exit
Router(config-bgp)#address-family ipv6 unicast
Router(config-bgp-af)#maximum-paths ebgp 256
Router(config-bgp-af)#commit

  3. Configure 256-multipath ECMP in eiBGP.

    Example:

    
Router(config)#router bgp 100
Router(config-bgp)#bgp router-id 10.10.10.11
Router(config-bgp)#address-family ipv4 unicast
Router(config-bgp-af)#maximum-paths eibgp 256
Router(config-bgp-af)#exit
Router(config-bgp)#address-family ipv6 unicast
Router(config-bgp-af)#maximum-paths eibgp 256
Router(config-bgp-af)#commit
2.

Verify the BGP multipath marking.

Example:

Router# show bgp 10.0.2.254/24

BGP routing table entry for 10.1.0.0/24
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker              11008       11008
Last Modified: Aug 14 13:59:39.403 for 00:00:05
Paths: (35 available, best #1)
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.101.3.2     
  Path #1: Received by speaker 0
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.101.3.2     
  Local, (received & used)
    10.0.101.1 from 10.0.101.1 (10.0.101.1)
      Origin IGP, localpref 100, valid, internal, best, group-best, multipath
      Received Path ID 0, Local Path ID 1, version 7708
  Path #2: Received by speaker 0
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.101.3.2     
  Local, (received & used)
    10.0.102.1 from 10.0.102.1 (10.0.102.1)
      Origin IGP, localpref 100, valid, internal, multipath
      Received Path ID 0, Local Path ID 6, version 11008
........
Path #256: Received by speaker 0
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.101.3.2     
  Local, (received & used)
    10.0.227.1 from 10.0.227.1 (10.0.227.1)
      Origin IGP, localpref 100, valid, internal, multipath
      Received Path ID 0, Local Path ID 6, version 14008
3.

Verify the BGP multipath marking in FIB.

Example:

Router# show cef 10.0.2.254/24

10.1.0.0/24, version 46115, internal 0x5000001 0x40 (ptr 0xd236928) [1], 0x0 (0xe715668), 0x0 (0x0)
 Updated Aug 14 13:59:39.007
 Prefix Len 24, traffic index 0, precedence n/a, priority 4
   via 10.0.101.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 0 NHID 0x0 [0xd236a00 0x0]
    next hop 120.0.101.1/32 via 120.0.101.1/32
   via 10.0.102.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 1 NHID 0x0 [0xde9a6d0 0x0]
    next hop 10.0.102.1/32 via 10.0.102.1/32
   via 10.0.103.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 2 NHID 0x0 [0xde9a010 0x0]
   ….
 via 10.0.227.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 255 NHID 0x0 [0xde9a010 0x0]
4.

Verify the BGP multipath marking in RIB.

Example:

Router# show route 10.0.2.254/24

Routing entry for 10.1.0.0/24
  Known via "bgp 1", distance 200, metric 0, type internal
  Installed Aug 14 13:59:38.971 for 00:11:48
  Routing Descriptor Blocks
    10.0.101.1, from 10.0.101.1, BGP multi path
      Route metric is 0
    10.0.102.1, from 10.0.102.1, BGP multi path
      Route metric is 0
    …
    10.0.227.1, from 10.0.227.1, BGP multi path
      Route metric is 0
5.

Verify the total number of IPv4 and IPv6 ECMP paths.

Example:

Router# show bgp ipv4 unicast 10.1.0.0/24 | i multipath | utility wc -l 
256

Router# show bgp ipv6 unicast 2001:DB8::1 | i multipath | utility wc -l 
256
6.

Verify the ECMP capabilities of the platform.

Example:

Router# show cef misc 
Platform capabilities:
--------------------------
L3 loadbalancing levels: 2
L3 Hash buckets: 64
L3 recursive Hash buckets: 256
L3 IP route Hash buckets: 256
L3 Unequal cost hash buckets: 64
L3 IP Unequal cost hash buckets: 256