I have 2x Arista 7050S in MLAG configuration and I configured IPv6 on them, IPv6 unicast routing is enabled, and I assigned 2aXX:XX:1::100/120 to interface vlan 80 and here is the interface vlan config:

   description XX
   ip address 172.XX.XX.41/30
   ipv6 address 2aXX:XX:1::101/120
   service-policy type pbr input PBR

my problem is IPv6 is working just on one of the MLAG member when I execute show ipv6 route and the other device show this error log:

%IP6ROUTING-4-DAD_FAILED: IPv6 DAD failed on interface VlanX for address 2aXX:XX:1::101
  • I have no problem with IPv4. I can set on both interface vlan without getting duplicate alert.

What is the problem?


There's a difference in Arista EOS on how virtual IPv4 addresses and virtual IPv6 addresses are configured.

Your configuration works for IPv4, but for IPv6 you need to configure both a unique and a 'virtual' IPv6 address. The virtual address is shared between the two devices in the MLAG pair, each device needs its own unique address.

The unique addresses are configured with the ipv6 address <addr> command, the virtual address with the ipv6 virtual address <addr>.

You're configuring the same unique address on both switches in the MLAG. As a result, a duplicate address is detected, which is the error message you get. So you need to configure the address you want to be available on both routers as virtual address, and assign two new unique addresses, one for each device.

I think Arista fixed this feature imparity between IPv4 and IPv6 in one of their latest releases.

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