Cisco Catalyst 9500-24Q ip helper-address problem

[eliemehawej]

Dears, 

I have a Cisco Cat 9500-24Q acting as Core Switch running the latest version 16.8.1a.

Under its SVIs interfaces, the command "ip helper-address x.x.x.x" pointing to an external DHCP server.

Users are being delayed to acquire a DHCP address from the external DHCP server (around 10-15 minutes).

Note that Users withing the same VLAN of the DHCP server are normally acquiring IP address.

Any idea on the above.

Thank you,

[bradfordb73]

Experiencing the same DHCP issue with an ip helper configured on multiple SVI's. Just interested to know if anybody has found a resolution to this issue.

[Andrew Khalil]

Dears @eliemehawej @bradfordb73,

Greetings,

It will be so helpful to share the wireshark capture from the user side to check the DHCP messags between the server and the clients!

A quick tip to troubleshoot, is to change the DHCP server and use another one just for testing, it can be virtual machine for example! to see whether the same problem exists or not, if yes, it means that it's a problem of the network while if it's not, it means that the problem of the server itself! 

Also, i would like to know, do you have any ACL applied on this vlan or not?

Sometimes, ACLs are affecting the performance of getting IPs from the DHCP servers! 

Please, don't forget to rate all helpful responses and mark solutions!

Bst Rgds,

Andrew Khalil 

[jpo1976]

Were you able to find a solution for this issue?

Thanks,

[eliemehawej]

Not yet.. still under TAC.. I will update once we have an answer.

[Suresh Varghese]

will u be able to share the configuration part where the IP helper address is configured on Nexus 

[Vincent Breton]

Look like i have the same issue with a 9500-12q

Can't get any ip address from dhcp for any client behind  9500

[Richard Burts]

The original post described the problem as very slow response in obtaining address assignment from DHCP server. It seems your problem is different and is that you do not receive any address at all. I suggest these steps to troubleshoot your issue:

1) post the configuration of the port where a user is experiencing this issue.

2) post the configuration of the vlan interface for the vlan where this user is located.

3) can you ping the address of the DHCP server specifying the source address for the ping as the address of the vlan interface.

4) can you verify that the DHCP server has a scope that is correctly configured for the subnet of that vlan interface.

5) are there any messages in the logs of the DHCP server indicating that it has received any requests from the subnet of that vlan interface.

HTH

Rick

[cassio.zillig]

Were you able to solve this problem?

[cassio.zillig]

I'm having the same problem on Catalyst 9500.

The device model is C9500 48Y4C and the IOS version I'm using is the 16.10.1 (Gibraltar)

[a.heck]

We have the same problem on C9500 48Y4C. We are using ios 16.12.4. Clients are waiting from 1às to more than 1minute to obtain an IP. Some times clients fall in timeout. Have anyone found a solution ?

[dorchard83]

Any update on this issue?

I’m having similar issue (up to 3 minutes to get an address).

C9500-16X running 16.8.1a.

Looking at upgrading to 16.9.3 to see if this helps.

[Vincent Breton]

Yes,
To make the "IP-Helper" command work properly through this kind of switch, we discover that you need to enable DHCP service with the "service dhcp" command in CLI.
We experimented other problems too with this switch... So, running 16.9.3 is a good thing, this version seem to be stable.

[dorchard83]

Thanks for the response!

We're getting addresses, but it's just really slow.

I've double checked the dhcp service anyway and it's already running.

Looks like upgrade to 16.9.3 is our next step, apparently 16.8.1a is known to have a lot of issues.

[uhabbe]

Looks a lot like bug CSCvq22224. 16.9.3 is known affected, "fixed" release not yet available for the public.