First-Hop Gateway Configuration Module

First-hop Gateway configuration module implements mechanisms used to implement a shared router IPv4 address on a stub access network.

The module supports statically configured anycast gateway IPv4 address and VRRPv3 for IPv4 and IPv6.

Platform Support

The module is supported on these platforms:

Operating system




Arista EOS

Aruba AOS-CX

Cisco Catalyst 8000v

Cisco CSR 1000v

Cisco IOSv

Cisco Nexus OS

Cumulus Linux

Dell OS10

Nokia SR OS

Nokia SR Linux


Global Parameters

The module supports the following global parameters:

  • gateway.protocol (default: anycast) – the first-hop gateway resolution protocol. The supported values are anycast and vrrp.

  • (default: -1) – the IP address within the subnet used for the gateway IP address

Anycast Gateway

The gateway configuration module supports IPv4 anycast gateways – MAC and IPv4 addresses shared between multiple nodes attached to the same segment.

Implementation Notes

  • The default netlab shared MAC address is

  • The gateway IP is configured to respond to ping requests

  • Vendors use different names for anycast gateways: VARP (Arista), VRR (Cumulus), passive VRRP (Nokia)

  • Arista EOS uses the same shared MAC address on all interfaces. Do not set link-level gateway.anycast.mac parameter in topologies using Arista EOS.

  • Arista vEOS cannot use VRRP MAC address as a shared MAC address (default recommended by Cumulus Linux)

Anycast Parameters

Anycast implementation of shared first-hop IPv4 address supports these parameters that can be specified globally or on individual links or interfaces.

  • gateway.anycast.unicast (default: True) – configure node-specific unicast IP addresses together with anycast IP address.

  • gateway.anycast.mac – Static MAC address used for the anycast IPv4 address


Many implementations require unique unicast IPv4 addresses configured on the interfaces that have anycast IPv4 address. Set gateway.anycast.unicast to False only when absolutely necessary.

Virtual Router Redundancy Protocol (VRRP)

netlab supports a single VRRPv3 instance per subnet/interface. The VRRPv3 instance can provide shared IPv4 and IPv6 addresses.


More complex topologies like multiple VRRPv3 instances on the same subnet could be deployed with a judicious application of interface parameters[1], but you won’t be able to model multiple VRRPv3 instances per interface[2].

VRRP Parameters

netlab supports these VRRP parameters that can be specified globally or on individual links or interfaces.

  • (default: 1) – VRRP group

  • vrrp.priority (interface parameter, integer)

  • vrrp.preempt (interface parameter, boolean)

No other aspect of VRRP (VRRP version, timers…) is manageable through netlab parameters, if you want to configured them create a plugin to implement additional VRRP functionality.