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.

--
Richard G. Harper [MVP Win9x] (E-Mail 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" <(E-Mail Removed)> wrote in message
news:A528F7F4-1D05-4A65-A141-(E-Mail Removed)...
> 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

As RGH says..^^

"Richard G. Harper" wrote:

> 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 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" <(E-Mail Removed)> wrote in message
> news:A528F7F4-1D05-4A65-A141-(E-Mail Removed)...
> > 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
>
>
>

Does the DHCP use separate scopes for each subnet or are you using
SuperScopes?

--

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

"Grant" <(E-Mail Removed)> wrote in message
news:A528F7F4-1D05-4A65-A141-(E-Mail Removed)...
> 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

Do not use Superscopes. Use separate individual Scopes for each subnet.

--

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

"Grant" <(E-Mail Removed)> wrote in message
news:A7C8FF52-A405-4C94-AB12-(E-Mail Removed)...
> 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" wrote:
>
> > Does the DHCP use separate scopes for each subnet or are you using
> > SuperScopes?
> >
> > --
> >
> > Phillip Windell [MCP, MVP, CCNA]
> > www.wandtv.com
> >
> > "Grant" <(E-Mail Removed)> wrote in message
> > news:A528F7F4-1D05-4A65-A141-(E-Mail Removed)...
> > > 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
> >
> >
> >