IMHO, the key info here is that a known set of subnets was affected. This rules out some stuff:
- LACP manages link bundling, as in “can this interface be added to the bundle?”. The effect of bundling should be to have multiple links to choose from when egressing a packet. RFC7130 is a nice addition to bundles as it uses BFD to manage each link - meaning a bad member is removed quickly (LACP timers are not that fast and LACP itself is not designed to react fast). - Hashing (which is used for load balancing traffic in hardware switches) is not managed by LACP - it’s always local to each device and as said before, each side usually has a different view of the ideal hashing. A classical example is when there are many IPs behind one firewall doing NAT - you can’t rely on diversity of IPs and MACs to select an egress link, so you usually change the hashing to be per port. - Link errors would affect random traffic to any destination / from any source So, none of the above technologies would affect traffic connectivity _selectively_. Perhaps a malformed bundle could blackhole traffic, but that wouldn’t be specific to certain subnets unless someone is *extremely* unlucky and _only_ his subnets hashed to the “bad bundle member” :) It simply looks like a routing issue through this path. Perhaps the flapping of the BGP session re-advertised this path to some place that previously wasn’t using it, and apparently can't? Pedro Martins Prado [email protected] / +353 83 036 1875 > On 28 Sep 2025, at 06:24, William Herrin via NANOG <[email protected]> > wrote: > > On Sat, Sep 27, 2025 at 7:31 PM Bruce Wainer via NANOG > <[email protected]> wrote: >> Excuse my ignorance about this IXP and your equipment, but is >> Micro-BFD (RFC 7130) supported? And if so, is it enabled or can you >> enable it? While configuration wise it will use the single IP >> addresses of the aggregate, separate BFD instances are set up for each >> underlying link and will confirm whether Layer 3 is working on that >> point-to-point connection. > > Hi Bruce, > > I'm also not familiar with this particular IXP but generally with IXPs > we're not talking about point to point connections. The multiple > participants' routers are part of a shared layer-2 fabric (a switch or > switches) over which they trade layer-3 packets directly with each > other. The route advertisements may transit the route servers but the > routed packets do not. > > You can get into some really finicky errors where both participants > successfully talk to the route server and thereby exchange routes, but > for one reason or another can't get packets back and forth to each > other. Bonded circuits (LAGs) add complexity which makes > troubleshooting that much harder. > > If it were me, I would have considered building this connection > differently. For speed, I'd have chosen a 100G link instead of two 10G > links. Had my objective been reliability, I'd have built that at layer > 3 instead of layer 2 -- two routers each with its own 10G link, and > then done some balancing of the advertised routes. But in all fairness > to Andy, I don't have anywhere near complete information here and the > details matter a lot. > > Regards, > Bill Herrin > > -- > William Herrin > [email protected] > https://bill.herrin.us/ > _______________________________________________ > NANOG mailing list > https://lists.nanog.org/archives/list/[email protected]/message/RXKZDTZBXR4VTGE7R6E55FHAC7QEVDHY/ _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/PNQLZYKGZRP5HTTDWOYSRB4372XHXUWO/
