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Webcast-Catalyst9k
New Member

Vlan issue?

Hi,

The problem I am having is this:

Two Cisco 3900 Switch Stacks with 2 VLANS setup (VLAN 1003 & 1005) connected via Fiber uplinks. The Workstations on the switch stack closest to the DHCP server can obtain an IP address, but workstations attached to the other switch stack cannot get an IP address. Any ideas???

Thanks,

Bob

9 REPLIES
Cisco Employee

Re: Vlan issue?

Where is the DHCP and w/s connected to? Different switches or same switch? Are the ports connected to in the same vlan? If you assign a static ip on the w/s could you ping the dhcp server? Are the two vlans corresponds to different ip subnet, and if so who is routing between them, that is if the w/s and DHCP server is on different vlans.

New Member

Re: Vlan issue?

We have 2 3900 (Token) Switch stacks connected via fiber uplink. Two Vlans on each both in the same ip subnet. 1 management and one data VLAN. Both Switch stacks are on the 10.11.0.0/16 subnet. We also have a 3640. All workstations attached to the switch stack that the dhcp server is connected to can obtain an ip address.

Workstations attached to the other switch stack(The remote stack connected via fiber) cannot obtain IP information from the DHCP server. The DHCP server is on the 10.11.0.0 subnet. If I both static IP's on the workstations attached to the remote stack, Eveything works great, they just can't obtain an IP address using DHCP. I have one switch stack configured as a VTP transparent, and the other stack I defined a VTP domain of CISCOA. Should they both be set to CISCOA?

Thanks,

Bob

New Member

Re: Vlan issue?

Bob:

Sorry about that! I wish I would have read this post before I sent my last reply asking about trunking.. This answered my question. To answer your VTP question.. The domain name only comes into play if you want to centrally manage your vlans. Making a vlan change on a vtp server propagates the change throughout the network to switches configured as vtp clients. If a switch is configured as vtp transparent, it ignores and only forwards vtp updates - vtp is basically disabled on it. Try sniffing on both sides of this and see if the dhcp discoveries/requests are ever getting to the server. And if so, does he reply..

New Member

Re: Vlan issue?

Bob:

A couple of questions: Are the workstations that can't obtain an IP address on the same vlan as the ones that can? Are the workstations that can't obtain an IP address on the same vlan as the DHCP server? And finally, do you have a router between the two vlans?

New Member

Re: Vlan issue?

Are the workstations that can't obtain an IP address on the same vlan as the ones that can?

Yes.

Are the workstations that can't obtain an IP address on the same vlan as the DHCP server?

Yes.

And finally, do you have a router between the two vlans?

I'm doing this work for a client. I haven't gotten that far yet. I know they have a 3640 connected to the token network.

Any Ideas??

Thanks,

Bob

New Member

Re: Vlan issue?

Hmm.. Interesting syptoms. As long as all of the hosts and the DHCP server are on the same vlan, the router doesn't come into play. Can you check to make sure that trunking is properly configured on the uplinks between the switches and the vlan in question is being trunked?

New Member

Re: Vlan issue?

when you say you have 2 vlans do you mean that you have a trcrf and a trbrf? since 1003 is the default trcrf and 1005 is the default trbrf, this isn't really 2 vlans, but have a parent child relationship, if I remember correctly, the trbrf needs unique bridge numbers for each switch did you change those, also did you set the ring number for the trcrf, they can be the same I believe, but it would be easier if they are different. hope this helps. So you would have Trbrf 1005 on each switch, one on bridge 0f, and one on bridge 0e, then define a trcrf under this trbrf of lets say ring 300 on one switch and 400 on the other switch. This should help.

New Member

Re: Vlan issue?

when you say you have 2 vlans do you mean that you have a trcrf and a trbrf?

Yes. 1003 & 1005

I'll take a closer look at the configs.

If you think of anything else, please let me know.

(Before I do anything more, I'm going to reboot both switch stacks) :-)

Thanks alot,

Bob

New Member

Re: Vlan issue?

Can you check to make sure that trunking is properly configured on the uplinks between the switches and the vlan in question is being trunked?

I'll take a look at the trunking setup. But if trunking wasn't setup properly, then it shouldn't work at all(If I assign a static IP to the workstations they work fine, they just can't obtain IP info from the DHCP server.)

Thanks Alot,

Bob

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