Posted on January 11, 2022 2:34 pm
 |  Asked by Farshid Abediny
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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?

Thank you.

Answered on January 11, 2022 2:48 pm

Hi Farshid,


MLAG is a L2 technology - it does turn both devices in a virtual single unit. However that is not true for L3. You will need separate addressing for each device - it's not the same as a stack, for example. DAD is detecting that the address is in use which is expected.

The easiest way to visualize this is thinking as if you had 2 routers connected to a single switch: you need to address the routers even if they are sharing VLANs on the switch. If you want gateway redundancy (FHRP), you can use VARP (preferred) or VRRP.

I hope this helps!




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