SFlow misconfiguration or bug on either the nexus or the sflow monitor? On the monitor, can you verify that the snmp interfaces are mapped to the correct ones on the nexus?
From: Mike Hammett <nanog@ics-il.net>
Sent: Monday, April 3, 2023 8:47 AM
To: Matthew Huff <mhuff@ox.com>
Cc: NANOG <nanog@nanog.org>
Subject: Re: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
It shows the desired result.
-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
Midwest-IX
http://www.midwest-ix.com
From:
"Matthew Huff" <mhuff@ox.com>
To: "Mike Hammett" <nanog@ics-il.net>, "NANOG" <nanog@nanog.org>
Sent: Monday, April 3, 2023 5:38:23 AM
Subject: RE: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
switch-core1# sh forwarding route x.x.x.x
slot 1
=======
IPv4 routes for table default/base
------------------+-----------------------------------------+----------------------+-----------------+-----------------
Prefix | Next-hop | Interface | Labels | Partial Install
------------------+-----------------------------------------+----------------------+-----------------+-----------------
x.x.x.x/24 x.x.x.250 Ethernet1/29
switch-core1# show routing hash x.x.x.x y.y.y.y
Load-share parameters used for software forwarding:
load-share mode: address source-destination port source-destination
Hash for VRF "default"
Hashing to path *y.y.y.y Eth1/29
For route:
y.y.y.0/24, ubest/mbest: 1/0
*via z.z.z.z, Eth1/29, [90/3072], 1w2d, eigrp-100, internal
From: NANOG <nanog-bounces+mhuff=ox.com@nanog.org> On Behalf Of Mike Hammett
Sent: Monday, April 3, 2023 1:21 AM
To: NANOG <nanog@nanog.org>
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