Re: Sites unreachable while traversing Dallas IXP

[Pierre LANCASTRE via NANOG <nanog () lists nanog org>]

Hi

Maybe you are now connected to 2 different remote devices in MLAG/VPC or
ESI, which could have MTU / routing table inconsistencies. So, as suggested
in some previous mails, did you try to deactivate the new link and keep the
bgp setup as it was originally?

Cordialement / Best regards

Pierre

Le ven. 26 sept. 2025, 11 h 06 a.m., Nick Hilliard via NANOG <
nanog () lists nanog org> a écrit :

> Mel Beckman wrote on 26/09/2025 15:32:
> >  From
> https://www.exam-labs.com/blog/configuring-lacp-between-cisco-ios-and-juniper-junos-a-step-by-step-guide
> >         *Understanding LACP Failures and Common Pitfalls*
> >
> > Link aggregation, although a robust feature, is susceptible to various
> > issues. To resolve these problems effectively, network administrators
> > must first understand the potential causes of LACP failures. Here are
> > some of the most common causes for LACP issues:
> >
> >  1. *Mismatched Configurations:**
> >     *Often, the primary reason for LACP failure is a misalignment in
> >     configurations between the two devices. This might include
> >     differences in LACP modes (active vs. passive), inconsistent
> >     port-channel settings, or mismatched VLANs. Proper alignment of
> >     settings across both devices is crucial to the successful
> >     negotiation of LACP.
>
> Not sure what this has to do with your previous email, where you were
> specifically referring to hashing algos needing to be the same or
> "compatible" on each side of the link:
>
> > Instead you configure one of the available hash-based distribution
> functions the two endpoints have in common.
>
> > I’ve found that sometimes with LAGs between different equipment vendors
> one or more of these algorithms aren’t compatible, resulting in packets out
> of order or even dropped.
>
> There's no such thing as the packet hashing algorithms needing to be
> "compatible" on each side of a LAG bundle. You can use whatever hashing
> algo you want on either side and it doesn't make the slightest
> difference at the other end. There's no concept of hashing algo
> compatibility, and hashing doesn't come into play with LACP or any other
> sort of negotiation.
>
> With the link above, you're confusing LACP negotiation issues with
> packet loss. If you have an LACP negotiation failure, typically the LAG
> interface won't come up to start with on a juniper / cisco device.
> Sometimes - rarely - you can have failure modes where an individual
> bearer circuit won't be used correctly, which would cause 1/N*100%
> packet loss, i.e. 50% if N=2.
>
> Also, as this is an IXP link, it probably means that it's a single
> untagged VLAN, i.e. no mismatched vlans.  Although if there is a
> mismatched vlan, then that vlan will experience 100% packet loss.
>
> Nick
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