Cisco Nexus 3k Route Selection\Packet Forwarding Debugging

Tue Apr 4 02:12:52 UTC 2023

You said that they are seeing traffic from another upstream…are you
advertising the prefix to them?  Are you advertising their prefix to your
upstream?

Looks like the route maps are involved in some dual redistribution…might
want to make sure everything is matching correctly, and being advertised
like you want.

On Mon, Apr 3, 2023 at 4:20 PM Mike Hammett <nanog at ics-il.net> wrote:

> I don't see any route-maps applied to interfaces, so there must not be any
> PBR going on. I only see ACLs, setting communities, setting local pref,
> etc. in the route maps that are applied to neighbors.
>
>
>
> -----
> Mike Hammett
> Intelligent Computing Solutions
> http://www.ics-il.com
>
> Midwest-IX
> http://www.midwest-ix.com
>
> ------------------------------
> *From: *"Mike Hammett" <nanog at ics-il.net>
> *To: *"Matthew Huff" <mhuff at ox.com>
> *Cc: *"NANOG" <nanog at nanog.org>
> *Sent: *Monday, April 3, 2023 8:26:30 AM
>
> *Subject: *Re: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
>
> Only two VRFs, default and manangement. IIRC, everything I saw before
> mentioned the default VRF.
>
> I do see a ton of route-maps. It's mostly Greek to me, so I'll have to dig
> through this a bit to see what's going on.
>
>
>
> -----
> Mike Hammett
> Intelligent Computing Solutions
> http://www.ics-il.com
>
> Midwest-IX
> http://www.midwest-ix.com
>
> ------------------------------
> *From: *"Matthew Huff" <mhuff at ox.com>
> *To: *"Mike Hammett" <nanog at ics-il.net>
> *Cc: *"NANOG" <nanog at nanog.org>
> *Sent: *Monday, April 3, 2023 8:06:51 AM
> *Subject: *RE: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
>
> What about VRFs and/or policy based routing?
>
> switch-core1# show vrf
> VRF-Name                           VRF-ID State   Reason
>
> default                                 1 Up      --
>
> management                              2 Up      --
>
>
> switch-core1# show route-map
> route-map rmap_bgp_to_eigrp_b2b, permit, sequence 10
>   Match clauses:
>     interface: Ethernet1/33
>     route-type: internal
>   Set clauses:
>     metric 40000000 10 255 1 1500
> route-map rmap_bgp_to_eigrp_b2b, permit, sequence 20
>   Match clauses:
>     interface: Ethernet1/34
>     route-type: internal
>   Set clauses:
>     metric 40000000 30 255 1 1500
> route-map rmap_static_to_eigrp, permit, sequence 10
>   Match clauses:
>     ip address prefix-lists: prefix_static_to_eigrp
>   Set clauses:
> route-map rmap_static_to_eigrp_v6, permit, sequence 10
>   Match clauses:
>     ipv6 address prefix-lists: prefix_ipv6_static_to_eigrp
>   Set clauses:
>
>
>
> From: Mike Hammett <nanog at ics-il.net>
> Sent: Monday, April 3, 2023 9:00 AM
> To: Matthew Huff <mhuff at ox.com>
> Cc: NANOG <nanog at nanog.org>
> Subject: Re: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
>
> It could be an sFlow bug, but I come at this from a reported problem and
> gathering data on that problem as opposed to looking at data for problems.
>
> The snmp if index reported by the Nexus matches the if index in ElastiFlow.
>
>
>
>
> -----
> Mike Hammett
> Intelligent Computing Solutions
> http://www.ics-il.com
>
> Midwest-IX
> http://www.midwest-ix.com
>
> ________________________________________
> From: "Matthew Huff" <mailto:mhuff at ox.com>
> To: "Mike Hammett" <mailto:nanog at ics-il.net>
> Cc: "NANOG" <mailto:nanog at nanog.org>
> Sent: Monday, April 3, 2023 7:50:08 AM
> Subject: RE: Cisco Nexus 3k Route Selection\Packet Forwarding Debugging
> 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 <mailto:nanog at ics-il.net>
> Sent: Monday, April 3, 2023 8:47 AM
> To: Matthew Huff <mailto:mhuff at ox.com>
> Cc: NANOG <mailto:nanog at 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" <mailto:mhuff at ox.com>
> To: "Mike Hammett" <mailto:nanog at ics-il.net>, "NANOG" <mailto:
> nanog at 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 <mailto:nanog-bounces+mhuff=ox.com at nanog.org> On Behalf Of
> Mike Hammett
> Sent: Monday, April 3, 2023 1:21 AM
> To: NANOG <mailto:nanog at 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
>
>
>
>
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