First-hop redundancy: one gateway address, two routers

The idea

A laptop reaches a server through two routers, routerA and routerB. They share one gateway address, so the laptop never notices one of them dying.

Steps

1. Two routers, one gateway address

   One gateway is one point of failure, so two routers share its address. The laptop's gateway is 10.0.1.254, an address no router was given. Both routers run VRRP and each has a virtual card, vrrp.1. Look at what that card holds on routerA, then on routerB.

   routerA:~# ip -br addr show vrrp.1
   routerB:~# ip -br addr show vrrp.1

2. A MAC address no card was born with

   Sharing the address is not enough: the laptop sends its frames to the gateway's MAC address, which it learned with ARP, and that must survive a failure too. Look at its neighbour entry for 10.0.1.254, then at routerA's virtual card.

   laptop:~# ip neigh show 10.0.1.254
   routerA:~# ip -d link show vrrp.1