Re: Best way to have redundancy announcing on separate routers

[Saku Ytti <saku () ytti fi>]

On Thu, 26 Dec 2024 at 17:51, Bryan Fields <Bryan () bryanfields net> wrote:

> I believe it was that one side was vlan tagged and the other wasn't or
> something to the effect of how the ISO MTU was calculated in the classic-IOS
> version vs. Junos.  As this was for less than a carrier grade setup (tactical
> deployment during an hurricane) I didn't have time to get deep into it.  A
> 3945e isn't exactly current anyway.  I think the other juniper involved was a
> 4500, so kind of in the same age as the cisco.

My money is that doing IPv4 ping with DF-bit on, you'd see loss from
one side with lower MTU. Likely the Junos side had a lower MTU, as you
are supposed to increase the IFD MTU by 4 if you add a VLAN encap,
which you do not need to do in 3945. However, personally if you're
going to have ifl's, I would set the ifd to maximum, and set ifls at
1500, so that when one ifl one day wants larger mtu, you don't have to
break the world.





-- 
  ++ytti