This is almost certainly the wrong solution to a real problem. Real
problem being, you have MTU mismatch, and the wrong solution is you
solve it for one ifa. You almost certainly want the MTU to be fixed in
ifl or maybe even ifd.
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.
Jean-
Yeah, don’t worry about people complaining.
Is this an accurate description of what you are trying to achieve?
- Have 2 different sets of prefixes that you announce. Set A via router1/ISP1 , Set B via router2/ISP2
- If BGP to one of your ISPs goes down, start announcing those prefixes to the other ISP. ( Example, if ISP2 goes down, start announcing prefix Set B over ISP1 )
Hi Tom,
This is exactly what I was planning.
I’m announcing a block via ISP1 and another set of blocks via ISP2, and have iBGP running between them.
Thanks a lot!!
Best regards,
Jean-
Thanks. Many BGP implementations have the ability to do conditional advertisements, where you announce (or don’t) a set of prefixes based on the presents (or absence) of other routes. I don’t think quagga does natively, and not sure if VyOS has added that on.
Conceptually, you want to be doing “announce these prefixes from this router only if I don’t see routes from the upstream on the other router”. The ‘safest’ way is probably to just monitor default, but it depends on your environment.
Jean-
Thanks. Many BGP implementations have the ability to do conditional advertisements, where you announce (or don't) a set of prefixes based on the presents (or absence) of other routes. I don't think quagga does natively, and not sure if VyOS has added that on.
Conceptually, you want to be doing "announce these prefixes from this router only if I don't see routes from the upstream on the other router". The 'safest' way is probably to just monitor default, but it depends on your environment.
That sort of thing seems like extra complexity, no?
If the 2 internal routers have iBGP and you are fairly sure that you
won't lose that path/view you should be able to just announce
the same prefixes to both ISP peerings and possibly add some
metric-equivalent data to distance one link vs the other, no?
(common metric for this is the as-path, add your as N times, where N
is <10 and > 2 probably?)
how exact do you want your split here to be jfranco ? (is 'mostly
everything over PRIMARY with some over SECONDARY' ok?)
I’m not saying I would do it, or you should do it, I’m just answering the questions being asked. 
I'm not saying I *would* do it, or you *should* do it, I'm just answering the questions being asked.
oh! fair enough... "that is a ton of complexity" still applies, or at
least for my view that's more complexity than: "always I announce to
all, with some metrics to make me seem there but just farther away on
link X"