topic Re: IP address conflict-Nexus 9k in Server Networking

IP address conflict-Nexus 9k

awilliams2 — Fri, 21 Feb 2020 23:33:40 GMT

Last week I had to power off all networking equipment to replace circuit breaker for the office. After work was complete all our network equipment powered on with no issues. Issue I have run into since then is getting IP address conflict notification from Meraki. My core switching for my two data centers are Nexus 9ks. I checked the MAC address for the conflict and its gateway for one of my VLANs. I am unsure what I need to do to get the ip address to not be on two different mac addresses. Let me know if you need more information to help me with this.

Re: IP address conflict-Nexus 9k

Francesco Molino — Sat, 22 Feb 2020 01:47:00 GMT

HI

You're getting an IP conflict issue. Did you found which VLAN has a conflict? Is it the IP on Nexus switches?
Can you share your config please?

Re: IP address conflict-Nexus 9k

balaji.bandi — Sat, 22 Feb 2020 13:37:26 GMT

what device IP and mac add you see a conflict here. how is your configuration and connection to that device?

Remove the device from the network in which you see the issue, clear the ip arp for that IP, see you still able to ping that IP.

Sometimes it may be VM in the network accidentally configured with templates, seen this many environments.

Re: IP address conflict-Nexus 9k

awilliams2 — Sat, 22 Feb 2020 19:51:49 GMT

It is VLAN 125. I am getting one mac address for one location and a different mac address on second data center, but both site are connected together which is causing the conflict

Re: IP address conflict-Nexus 9k

awilliams2 — Sat, 22 Feb 2020 21:18:50 GMT

Conflict for VLAN 125 ip 10.20.125.1

00:00:0C:9F:F0:7D- This is showing on LAB side

00:00:0C:07:AC:7D- Seen on HQ or VI side

Re: IP address conflict-Nexus 9k

balaji.bandi — Sat, 22 Feb 2020 22:09:42 GMT

as per the information, it looks like this is another side of the device MAC address, do you have a high-level network diagram of how these connections, and do you have any other source other than VPC connection these switches.

i see one of the trunks allowed this VLAN 125, where is that going to?

can you provide hsrp output from both the switches?

Re: IP address conflict-Nexus 9k

awilliams2 — Sat, 22 Feb 2020 22:39:49 GMT

trunk vlan 125 is going to our storage.

GT-9K-TOP

Vlan125 - Group 125 (HSRP-V2) (IPv4)
Local state is Standby, priority 100 (Cfged 100), may preempt
Forwarding threshold(for vPC), lower: 0 upper: 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.201000 sec(s)
Virtual IP address is 10.20.125.1 (Cfged)
Active router is 10.20.125.4, priority 100 expires in 7.960000 sec(s)
Standby router is local
Authentication text "cisco"
Virtual mac address is 0000.0c9f.f07d (Default MAC)
3 state changes, last state change 1y38w
IP redundancy name is hsrp-Vlan125-125 (default)

VI-9K-TOP

Vlan125 - Group 125 (HSRP-V1) (IPv4)
Local state is Active, priority 200 (Cfged 200), may preempt
Forwarding threshold(for vPC), lower: 0 upper: 200
Preemption Delay (Seconds) Minimum:300
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.422000 sec(s)
Virtual IP address is 10.20.125.1 (Cfged)
Active router is local
Standby router is 10.20.125.5 , priority 100 expires in 8.010000 sec(s)
Authentication text "cisco"
Virtual mac address is 0000.0c07.ac7d (Default MAC)
5 state changes, last state change 1d08h
IP redundancy name is hsrp-Vlan125-125 (default)

Re: IP address conflict-Nexus 9k

balaji.bandi — Sat, 22 Feb 2020 22:53:21 GMT

I do not see any issue around the design and config.

only difference i see you post other config has below config- but your HSRP output shows 4 and 5 ? so are we missing something here ? how many device particiapating in the HSRP, how are they connected ?

interface Vlan125
description BUILD
no shutdown
no ip redirects
ip address 10.20.125.3/24
ip router eigrp 110
ip passive-interface eigrp 110
hsrp 125
preempt delay minimum 300
priority 200
ip 10.20.125.1

Re: IP address conflict-Nexus 9k

awilliams2 — Sun, 23 Feb 2020 00:13:48 GMT

There is 4 devices total

HQ(VI) 9k Top & 9k BTM

Lab(GT) 9k Top & 9k BTM

Re: IP address conflict-Nexus 9k

balaji.bandi — Sun, 23 Feb 2020 00:18:10 GMT

can you post all hsrp output to understand.

Re: IP address conflict-Nexus 9k

awilliams2 — Sun, 23 Feb 2020 00:20:11 GMT

Re: IP address conflict-Nexus 9k

balaji.bandi — Sun, 23 Feb 2020 08:22:46 GMT

Sorry i may said wrong, i am more intersted to all HSRP from all device related to VLAN125,

After reviewing some information again, you have 2 HSRP segement, and streched across DC, then you need to block VIP hsrp MAC address not to stretch across 2 DC. (this we can only confirm based on design)

Re: IP address conflict-Nexus 9k

awilliams2 — Mon, 24 Feb 2020 04:45:34 GMT

I just noticed that vlan 125 on one side is using HSRP v1 and vlan 125 is using HSRP v2 at other side

Re: IP address conflict-Nexus 9k

balaji.bandi — Mon, 24 Feb 2020 08:09:08 GMT

thanks for the clarification and make sense, different version in the network. hope all sorted by now.