3

My understanding of Arista's implementation of MC-LAG is relatively weak, so its likely I've misunderstood a deliberate limitation of how the mlag works.

Taking a basic example,

Mlag

Where,

switch1: 
  vlan10-svi: 192.168.0.1/24
switch2: 
  vlan10-svi: 192.168.0.2/24
switch3: 
  vlan10-svi: 192.168.0.3/24

So in a given scenario of switch3 pinging each of the SVI's on switch1 and switch2, I'd expect to see,

# ping 192.168.0.1
80 bytes from 192.168.0.1: icmp_req=1 ttl=64 time=0.338 ms
# ping 192.168.0.2
80 bytes from 192.168.0.2: icmp_req=1 ttl=64 time=0.338 ms

Whereas in reality,

# ping 192.168.0.1
80 bytes from 192.168.0.1: icmp_req=1 ttl=64 time=0.338 ms
# ping 192.168.0.2
1 packets transmitted, 0 received, 100% packet loss, time 0ms

It is also the same when attempting to ping each respective SVI from switch1 <=> switch2.

If the either port on the portchannel on switch3 is shutdown - then reachability of each respective switch is possible - but it is never possible to ping both switch1 and switch2.


Now, I understand that VARP is likely the tool used to allow reachability of both devices (and in fact, does); but in the example where each switch needs to be independently accessed (eg. for management outside of ma1) - it doesn't appear to be possible.

  • Is this simply L3 limitation/design of Arista's MLAG?
  • Should it be possible to ping between the mlag peers (not using the mlag peer link)
  • Should it be possible for switch3 to be able to ping both switch1 and switch2

1 Answer 1

2

It would appear this is a simple one.

I believed that the peer link should only contain the mlag communication VLAN (rather than everything), so on the peer link port channel simply replacing,

switchport trunk allowed vlan 4094

With

switchport trunk allowed vlan 10,4094

Immediately provided ICMP response from both sw3 to sw1,sw2 and between sw1 and sw3.

show spanning tree confirms there are no blocked interfaces, so Arista is clearing working some voodoo to prevent L2 loops with the mlag peer link.

2
  • You should accept this answer so that the question doesn't keep popping up and looking for an answer.
    – Ron Maupin
    Jul 7, 2016 at 0:00
  • Done and done sir
    – choco-loo
    Jul 7, 2016 at 17:41

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