[c-nsp] Cisco Nexus 3k Route Selection\Packet Forwarding Debugging

[Mike Hammett]

The snmp if index reported by the Nexus matches the if index in ElastiFlow. 




----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

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

From: "Raymond Burkholder via cisco-nsp" <cisco-nsp at puck.nether.net> 
To: cisco-nsp at puck.nether.net 
Sent: Monday, April 3, 2023 12:31:59 AM 
Subject: Re: [c-nsp] Cisco Nexus 3k Route Selection\Packet Forwarding Debugging 

On 4/2/23 23:16, Mike Hammett via cisco-nsp wrote: 
> 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? 

A couple points of view: 
a) what you are explaining is what you see in the 'gui' 
b) what you are explaining is what you see in the individual sflow records 
c) routing information base has something else 

For a) 

Sflow may be sending out an interface index. 

Interface indexes may change unless forced not to do so. 

An interface name comes from a different command. 

Index and name may not be in sync. 

For b) 

No idea. 

for c) 

Did you look in the routing table / cef table to see what the actual 
destination is? Rather than what BGP shows you? 
> 
> 
> 
> 
> ----- 
> Mike Hammett 
> Intelligent Computing Solutions 
> 
> Midwest Internet Exchange 
> 
> The Brothers WISP 
> 
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