DHCP Server, multiple VLANs

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Greetings list,

I have been experiencing a few problems lately with my DHCP server. We have
several VLANs in our network all serviced by the same DHCP server, and
clients are having a difficult time roaming between subnets.

For instance, a user typically resides on subnet A, but attends a meeting
in subnet B. He brings his laptop to the meeting and plugs in and attempts
to get an address on subnet B. The laptop ends up getting the same address
they used in subnet A and of course it does not work because it is the wrong
subnet.

I have done a packet trace on the DHCP server, and it appears that the
client, during the DHCP Discover phase, does request the old address, and the
DHCP server allows the request in the DHCP Offer phase.

We are using Cisco's ip-helper address command on the Catalyst switches to
relay the DHCP broadcasts. This problem has occured regardless of the
subnet, i.e. on the same subnet as the DHCP server itself.

Any commments or suggestions are most welcome.

Thanks,

Grant
 
What you're seeing is how DHCP is supposed to work. You should be able to
work around it by having the laptop user do an IPCONFIG /RELEASE followed by
an IPCONFIG /RENEW - that should put things to rights.
 
As RGH says..^^

Richard G. Harper said:
What you're seeing is how DHCP is supposed to work. You should be able to
work around it by having the laptop user do an IPCONFIG /RELEASE followed by
an IPCONFIG /RENEW - that should put things to rights.

--
Richard G. Harper [MVP Win9x] (e-mail address removed)
* PLEASE post all messages and replies in the newsgroups
* for the benefit of all. Private mail is usually not replied to.
* HELP us help YOU ... http://www.dts-l.org/goodpost.htm


Grant said:
Greetings list,

I have been experiencing a few problems lately with my DHCP server. We
have
several VLANs in our network all serviced by the same DHCP server, and
clients are having a difficult time roaming between subnets.

For instance, a user typically resides on subnet A, but attends a meeting
in subnet B. He brings his laptop to the meeting and plugs in and
attempts
to get an address on subnet B. The laptop ends up getting the same
address
they used in subnet A and of course it does not work because it is the
wrong
subnet.

I have done a packet trace on the DHCP server, and it appears that the
client, during the DHCP Discover phase, does request the old address, and
the
DHCP server allows the request in the DHCP Offer phase.

We are using Cisco's ip-helper address command on the Catalyst switches to
relay the DHCP broadcasts. This problem has occured regardless of the
subnet, i.e. on the same subnet as the DHCP server itself.

Any commments or suggestions are most welcome.

Thanks,

Grant
Click to expand...
Click to expand...
 
Do not use Superscopes. Use separate individual Scopes for each subnet.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

Grant said:
A combination of both, actually. I am not familiar with the effective
difference, I guess I will have to read up on that. Which should it be?



Phillip Windell said:
Does the DHCP use separate scopes for each subnet or are you using
SuperScopes?

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

Grant said:
Greetings list,

I have been experiencing a few problems lately with my DHCP server.
Click to expand...
We
have
several VLANs in our network all serviced by the same DHCP server, and
clients are having a difficult time roaming between subnets.

For instance, a user typically resides on subnet A, but attends a meeting
in subnet B. He brings his laptop to the meeting and plugs in and attempts
to get an address on subnet B. The laptop ends up getting the same address
they used in subnet A and of course it does not work because it is the wrong
subnet.

I have done a packet trace on the DHCP server, and it appears that the
client, during the DHCP Discover phase, does request the old address,
Click to expand...
and
the
DHCP server allows the request in the DHCP Offer phase.

We are using Cisco's ip-helper address command on the Catalyst switches to
relay the DHCP broadcasts. This problem has occured regardless of the
subnet, i.e. on the same subnet as the DHCP server itself.

Any commments or suggestions are most welcome.

Thanks,

Grant
Click to expand...
Click to expand...
Click to expand...
 
Back
Top