Re: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging

[Mike Hammett <nanog () ics-il net>]

"partial tables" 

There were only 292 IPv4 routes, which was expected. The IPv6 routes were expected to be less. There were 118k IPv6 
routes in a box that could only handle... 4k? 


Fixed that errant IPv6 fill and all is well. Well, seemingly anyway. I won't rule out a coincidence, but these seems 
like a direct line from problem to resolution. 





----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

----- Original Message -----

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? 




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

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