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I have an odd situation. There is static route on my Nexus 7700 that routes anything for specific subnet /24 to a F5 LTM Load Balancer, external VRRP interface 10.x.153.15.

As you can see below, the old host 10.x.135.70 is working fine which is using an AM Adjacency route using nexus FIB table with a 250 cost.

The new server 10.x.135.71 that is not working is using a standard static route cost of 1, I guess using the nexus RIB table.

At the moment we can route to .70 fine which is using the AM Route but not .71 which is using the Static Route. No new routes have been added. I'm using the /24 route to the F5 LB 10.x.135.15 already on the switch.

I've performed a debug on the Load balancer and I can see the F5 Interface 10.x.153.15 (external interface) quite rightly asking 10.x.135.13 (Nexus Switch Vlan interface) for an ARP. It receives no reply because the Nexus switch is not resolving the ARP of 10.x.135.71. I can ping the host fine from the switch. The Server .71 is configured correctly DG & Subnet

F5

3661  23.056618 0.000228 137 F5Networ_15:76:07 → Broadcast       ARP OUT s1/tmm0 : Who has 10.x.135.71? Tell 10.x.135.13

How do I make the new server 10.x.135.71 part of the AM routing table and shouldn't the FIB automatically find and assign the new server ARP to it's table? I even contacted F5 they went through issue and said this is a Cisco Switch issue!

Switch A# sh ip route 10.x.135.70  
IP Route Table for VRF "default"  
'*' denotes best ucast next-hop  
'**' denotes best mcast next-hop  
'[x/y]' denotes [preference/metric]  
'%<string>' in via output denotes VRF <string>  
10.x.135.70/32, ubest/mbest: 1/0, attached  
via 10.x.135.70, Vlan137, [250/0], 5d11h, am  
Switch A #

Switch A# sh ip route 10.x.135.71  
IP Route Table for VRF "default"  
'*' denotes best ucast next-hop  
'**' denotes best mcast next-hop  
'[x/y]' denotes [preference/metric]  
'%<string>' in via output denotes VRF <string>  
10.x.135.0/25, ubest/mbest: 1/0  
via 10.x.153.15, [1/0], 51w3d, static  
Switch A#



Switch A# sh ip arp 10.x.135.70  
Flags: * - Adjacencies learnt on non-active FHRP router  
+ - Adjacencies synced via CFSoE  
- Adjacencies Throttled for Glean  
D - Static Adjacencies attached to down interface  
IP ARP Table  
Total number of entries: 1  
Address Age MAC Address Interface  
****10.x.135.70 00:06:51 x.x.817c Vlanx**  
Switch A# sh ip arp 10.x.135.71  
Flags: * - Adjacencies learnt on non-active FHRP router  
+ - Adjacencies synced via CFSoE  
- Adjacencies Throttled for Glean  
D - Static Adjacencies attached to down interface  
IP ARP Table  
Total number of entries: 0  
Address Age MAC Address Interface  
Switch A#  
5
  • 1
    You need to provide your outputs using proper formatting. This looks like a jumbled mess to read. – Jesse P. Nov 13 '19 at 13:06
  • 1
    Please use the Preformatted-text feature ({}) for outputs to your device commands. This will preserve the original text formatting so that we can read it as you did. Also, please refer to the Network Engineering Question Checklist for guidance on what to include in your question. – Ron Maupin Nov 13 '19 at 14:37
  • Please edit your question to include the interface configuration and static routes. We can't diagnose the problem with the limited information – Ron Trunk Nov 13 '19 at 16:42
  • Also, you don't need to redact your second octet. That's a private subnet - it's not like you're creating a security issue by sharing all 4 octets. You're only making it harder for us to troubleshoot, since we now have to assume that the second octet is correct. – Jesse P. Nov 13 '19 at 17:06
  • Apologies about this format. In regards to sharing all four octets. I left about the 2nd octet for security reasons. It's unlikely the 2nd octet would be different though I will make the comment next time to not confuse others. – mortirolo Nov 14 '19 at 13:12
3

I've solved the issue!

It appears there were inconsistencies in the FIB table of the Nexus 7700

if you run this command, this will show any inconsistencies, which included my host IP

test forwarding ipv4 inconsistency

then run

clear forwarding ipv4 route 10.x.135.71

this command will populate the route again into the FIB table. After the route appeared correctly with the correct cost and I was able SSH to the host and ping

1
  • Cool. Don't forget to accept your answer so this is marked as solved. – Jesse P. Nov 14 '19 at 12:03

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