No ip addresses are being assigned to PC's from Router

Unanswered Question
Sep 23rd, 2010

I have a problem with one of my sites that I need to fix.

I created a configuration that goes on the router which has multiple vlans and each vlan has it's own IP DHCP pools that is assigned to it.

The problem that I am experiencing is that whenever I upload the config to the Cisco 2851 router it does not give out the ip addresses from the router.

I can ping from the router to any of my other sites, but cannot get IP addresses for the PC's.

I have a Cisco 2851 Voice router that connects to a 3750 stack. The 3750 stack than connects to two other 3750 stacks in different areas via fiber connection.

The current config is working as follows:

Cisco 2851 router connects to the 3750 stack which is setup as a Layer 3. The 3750 stack connects to the other two 3750 stacks via fiber connection.

Attached is the new configs for the site.

I have this problem too.
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Stephen Leach Thu, 09/23/2010 - 02:44

Hi Shawn,

I have not had the opportunity as yet to look through all of the configs and only read your overview. So an initial thought was that if you are crossing a Layer 3 boundary you may need 'ip helper address' to get broadcasts to the next hop, and I would also ensure you are not filtering out the DHCP broadcasts anywhere in the path?

Work permitting I may get a chance to look at the configs later.



shawn.lewis Thu, 09/23/2010 - 04:27

Hi There

Much appreciated. The strange part of this is that I have setup a small lab environment in the office and used the same configs on the router and switch and it works. We tested it with about six technicians PC's and they were getting ip addresses from the router.

The current config is setup so that the switch is acting as a Core switch and running layer 3. The new config is changed so the router does all the routing and the switch is setup as a layer two access switch.

glen.grant Thu, 09/23/2010 - 05:53

   On your first hop switch you have this  " no vlan 3,7,8,10,11,16"  , is this valid ? 

This would remove all your l2 vlans  and your trunks would not work.  Also I would remove spanning tree portfast on links between switches.  On SW2 and 3 I don't see where you have turned off ip routing  like you did on Sw1 .

shawn.lewis Thu, 09/23/2010 - 06:20

Much appreciated. I have been changing the configs to see what will work and what does not work. I have fixed the configs accordingly and will test in the lab environment before doing it on the Live environment.

Attached is the updated configs.

pughaz1330 Thu, 09/23/2010 - 06:07


Thanks & Regards

D.Pugalendi. Senior Consultant (Networks), TAFE Ltd.,

35,Nungambakkam High Road, Chennai 34,Phone - 044-32977969 ; 9962017117


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