11-17-2021 02:06 AM
Hi,
Got problem in logs on cisco Nexus 6001:
%ARP-3-REQ_IP: arp [3857] Sending ARP request for invalid IP address 0.0.0.0 on Null0, request from pid: 3981
To reproduce this error I simply should make route to 1.104.196.17 unavailable
# show ip route 1.150.62.0/23 1.150.62.0/23, ubest/mbest: 1/0 *via 1.104.196.17, [1/0], 18:35:22, static via Null0, [254/0], 3y23w, static
To make it unavailable need to take down or simply remove 1.104.196.17 static route.
# show ip interface vlan 951 IP Interface Status for VRF "default"(1) Vlan951, Interface status: protocol-up/link-up/admin-up, iod: 292, IP address: 1.104.196.18, IP subnet: 1.104.196.16/30 route-preference: 0, tag: 0 Btw, 1.104.196.18 also my router-id.
After Null0 route becomes best %ARP-3-REQ_IP is generated.
How can I find what is sending arp requests?
11-17-2021 03:09 AM
Hi,
This is the default behaviour of Cisco router when it got a static route pointing to a next-hop IP address pointing through an Ethernet interface.
The static route is pointing to x.x.x.17 for which Router is not getting ARP reply.
Please look into the below detailed document to understand your issue as well as solutions.
Static Routes With Next Hop As An Exit Interface Or An IP Address - Cisco Community
11-17-2021 06:30 AM
Thanks, let me clarify.
This is valid for Null0 routes like
1.150.62.0/23, ubest/mbest: 1/0 *via Null0, [254/0], 3y23w, static
What address arp tries to determine in case of Null0 interface?
P.S. In my case after deleting both static routes resolved issue
no ip route 1.150.62.0/23 1.104.196.17 no ip route 1.150.62.0/23 Null0 254
But I don't understand why arp try to work on Null0 interface.
11-17-2021 08:42 AM
11-17-2021 11:26 PM - edited 11-18-2021 12:03 AM
This ok, but how to describe such behavior after deleting static route 1.104.196.17:
# show ip route 91.250.62.0/23 1.150.62.0/23, ubest/mbest: 1/0 *via Null0, [254/0], 00:00:05, static
With only Null route nexus generates %ARP-3-REQ_IP: arp [3857] Sending ARP request for invalid IP address 0.0.0.0 on Null0, request from pid: 3981 message.
Deleting Null route stops generating arp log message.
Moreover another Null0 static routes doesn't generate such arp messages.
Maybe some internal process try to generate arp for certain routes?
And maybe I can somehow watch what arp enables this error message?
I find process by pid but don't find more information.
# show processes | include 3981
3981 S 415c4642 1 - rpm
Thanks in advance.
11-18-2021 07:54 AM
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