DHCP on a VLAN

[Raul102801]

Hi I have a tricky situation and can't figure out how to take care of it. I am rebuilding our DHCP server and while I find the time to get that done, have setup our pix to issue DHCP to the PC VLAN. I have 3 more VLANs and have found the following problem. If I let the PIX issue DHCP then the PC VLAN can't talk to the servers on the other VLANs, if I setup a static IP address and se my gateway to the VLANs IP address I can ping anything on the other VLANs but can't get online. If I let the PIX do the DHCP, the members of the VLAN set the gateway to the Pix's addressand I can get online but can't see other VLAN's. The PC VLAN is the only one with DHCP, everything else has static IP addresses. Everything is connected to a cisco catalyst 6509 switch.

Any ideas or tips?

Thanks

 

[gwildfire]

you need to configure the IP helper address (add of the DHCP server) on each Vlan interface

so

conf t
Interface vlan X
ip helper-add x.x.x.x

This allows broadcasts such as a DHCP request to transit a layer 3 boundry, however it should be noted that it forwards a series of other services by default such as netbios services which can cause network congestion.

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http://www.Cisco-Engineer.com

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[castlesmadeofsand]

Are you seeing the pc's getting an ip from the pix? If so, gwildfire, then that is not the issue. If the pix is giving out dhcp addresses, then it is obviously broadcasting. I do know that you need the helper address command to have a router forward certain broadcasts, protocols like tacacs and dhcp.

Jimi

 

[MattWray]

When everything is working, what is doing the routing? Sounds like a possible routing issue to me.


Matt Wray

http://www.sss-steel.com

 

[Raul102801]

The 6509 does the routing. PCs are getting an IP from the PIX but they also set the gateway to the PIXs address not the VLAN address. Is this the way is supposed to be? if so what do I need to do to see other VLANs? I guess I'll go ahead and configure IP helper and go from there.

I'll post the results
Thanks

 

[MattWray]

I think the problem is when you set the gateway to the PIX for the PC VLAN, the PIX does not know the way to the other VLANs.

You could either try static routes in the PIX (if you don't have them) or set your 0.0.0.0 in the 6509 to the PIX and use the static addresses.


Matt Wray

http://www.sss-steel.com

 

[octavian10]

I think you need to setup the pix DHCP to issue a layer 3 port on the 6509 as the gateway. This port should then be programed for inter VLAN routing. Pix's cannot perform inter VLAN routing (router on a stick) so having the PIX as your gateway is most likley your problem.

"I hear and I forget. I see and I remember. I do and I understand."
- Confucius (551 BC - 479)

 

[Raul102801]

You guys are correct, this is an old Pix which won't do vlans. I finally got the drives I need for my DHCP server so I'll configure that today and take DHCP out of the PIXs plate.


Thanks everyone for the great advise