We did have our common upstream provider perform maintenance that then afterwards, had the traffic flowing on the right path. Later activity on our direct connection pushed it back to the common upstream. We haven't yet had the opportunity to bump our BGP session with the common upstream provider, but I suspect that will put the traffic back onto the right path. Seems like the router is just hanging onto the oldest BGP session it has, regardless of any other parameter or configuration.

This seems like a bug. We do intend on upgrading NX-OS, but that's on someone else's schedule.



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Mike Hammett
Intelligent Computing Solutions

Midwest Internet Exchange

The Brothers WISP

From: "Mike Hammett" <nanog@ics-il.net>
To: "NANOG" <nanog@nanog.org>
Sent: Monday, April 3, 2023 12:21:29 AM
Subject: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging

We have a Nexus 3064 that is setup with partial BGP tables and is routing based on that. 


I've done a show ip bgp for an IP of interest and it has an expected next hop IP. I show ip arp on that next hop IP and it has the expected interface. 


However, sFlows show the packets leaving on a different interface, the one that would carry the default route for routes not otherwise known. 


If the next hop IP is expected and the ARP of that next hop IP is expected, why are packets leaving out an unexpected interface? 



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Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com

Midwest-IX
http://www.midwest-ix.com