On Thu, 26 Dec 2024 at 17:51, Bryan Fields <br...@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
