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Equal Cost Multipath Routing with Zebra

This page explains how GoBGP handles Equal Cost Multipath (ECMP) routes with Zebra daemon included in Quagga or FRRouting.

Prerequisites

Assume you finished Getting Started and FIB manipulation.

Contents

Configuration

Note: Before constructing your environment, please confirm your Zebra is built with "--enable-multipath=ARG" configure option. The APT packaged Quagga on Ubuntu 16.04 is configured with this option as following.

$ /usr/lib/quagga/zebra --version
zebra version 0.99.24.1
Copyright 1996-2005 Kunihiro Ishiguro, et al.
configured with:
	--build=x86_64-linux-gnu ...(snip)... --enable-multipath=64 ...(snip)...

Here supposes the following topology and demonstrates two ECMP routes which advertised from R2 and R3 are installed to R1's Kernel routing table via Zebra.

R1: GoBGP + Zebra
R2: GoBGP
R3: GoBGP

    +-------------+                     +-------------+
    | R1          | .1/24         .2/24 | R2          |
    | ID: 1.1.1.1 |---------------------| ID: 2.2.2.2 |
    | AS: 65000   |   192.168.12.0/24   | AS: 65000   |
    +-------------+                     +-------------+
        | .1/24
        |
        | 192.168.13.0/24
        |
        | .3/24
    +-------------+
    | R3          |
    | ID: 3.3.3.3 |
    | AS: 65000   |
    +-------------+

To enables ECMP features at GoBGP on R1, please confirm "use-multiple-paths" option is configured as following. With this option, GoBGP will redistribute BGP multipath routes to Zebra and Zebra will install them into Kernel routing table.

# gobgpd.toml on R1

[global.config]
  as = 65000
  router-id = "1.1.1.1"

[global.use-multiple-paths.config]
  enabled = true

[[neighbors]]
  [neighbors.config]
    neighbor-address = "192.168.12.2"
    peer-as = 65000
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv4-unicast"
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv6-unicast"

[[neighbors]]
  [neighbors.config]
    neighbor-address = "192.168.13.3"
    peer-as = 65000
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv4-unicast"
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv6-unicast"

[zebra.config]
  enabled = true
  url = "unix:/var/run/quagga/zserv.api"
  redistribute-route-type-list = ["connect"]
  version = 2
# gobgpd.toml on R2

[global.config]
  as = 65000
  router-id = "2.2.2.2"

[[neighbors]]
  [neighbors.config]
    neighbor-address = "192.168.12.1"
    peer-as = 65000
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv4-unicast"
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv6-unicast"
# gobgpd.toml on R3

[global.config]
  as = 65000
  router-id = "3.3.3.3"

[[neighbors]]
  [neighbors.config]
    neighbor-address = "192.168.13.1"
    peer-as = 65000
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv4-unicast"
  [[neighbors.afi-safis]]
    [neighbors.afi-safis.config]
      afi-safi-name = "ipv6-unicast"

Verification

When connections established between each routers, all routers have only "connected" routes from Zebra on R1.

R1> gobgp global rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
*> 1.1.1.1/32           0.0.0.0                                   00:00:00   [{Origin: i} {Med: 0}]
*> 192.168.12.0/24      0.0.0.0                                   00:00:00   [{Origin: i} {Med: 0}]
*> 192.168.13.0/24      0.0.0.0                                   00:00:00   [{Origin: i} {Med: 0}]

R2> gobgp global rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
*> 1.1.1.1/32           192.168.12.1                              00:00:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 192.168.12.0/24      192.168.12.1                              00:00:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 192.168.13.0/24      192.168.12.1                              00:00:00   [{Origin: i} {Med: 0} {LocalPref: 100}]

And only these routes are installed on R1's Kernel routing table.

R1> ip route
192.168.12.0/24 dev r1-eth1  proto kernel  scope link  src 192.168.12.1
192.168.13.0/24 dev r1-eth2  proto kernel  scope link  src 192.168.13.1

Then, let's add new routes destinated to "10.23.1.0/24" on R2 and R3 routes. These routes should be treated as Multipath routes which have the same cost.

R2> gobgp global rib -a ipv4 add 10.23.1.0/24
R2> gobgp global rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
*> 1.1.1.1/32           192.168.12.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 10.23.1.0/24         0.0.0.0                                   00:00:00   [{Origin: ?}]
*> 192.168.12.0/24      192.168.12.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 192.168.13.0/24      192.168.12.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]

R3> gobgp global rib -a ipv4 add 10.23.1.0/24
R3> gobgp global rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
*> 1.1.1.1/32           192.168.13.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 10.23.1.0/24         0.0.0.0                                   00:00:00   [{Origin: ?}]
*> 192.168.12.0/24      192.168.13.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]
*> 192.168.13.0/24      192.168.13.1                              00:10:00   [{Origin: i} {Med: 0} {LocalPref: 100}]

GoBGP on R1 will receive these routes and install them into R1's Kernel routing table via Zebra. The following shows that traffic to "10.23.1.0/24" will be forwarded through the interface r1-eth1 (nexthop is R2) or the interface r1-eth2 (nexthop is R3) with the same weight.

R1> gobgp global rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
*> 1.1.1.1/32           0.0.0.0                                   00:15:00   [{Origin: i} {Med: 0}]
*> 10.23.1.0/24         192.168.12.2                              00:05:00   [{Origin: ?} {LocalPref: 100}]
*  10.23.1.0/24         192.168.13.3                              00:05:00   [{Origin: ?} {LocalPref: 100}]
*> 192.168.12.0/24      0.0.0.0                                   00:15:00   [{Origin: i} {Med: 0}]
*> 192.168.13.0/24      0.0.0.0                                   00:15:00   [{Origin: i} {Med: 0}]

R1> ip route
10.23.1.0/24  proto zebra
	nexthop via 192.168.12.2  dev r1-eth1 weight 1
	nexthop via 192.168.13.3  dev r1-eth2 weight 1
192.168.12.0/24 dev r1-eth1  proto kernel  scope link  src 192.168.12.1
192.168.13.0/24 dev r1-eth2  proto kernel  scope link  src 192.168.13.1