dhcp issue

[yanhui-wang]

I am trying to setup router as dhcp server. for data vlan(vlan 1) and voice vlan(vlan 2). voice vlan works fine but dhcp doesn't work on data vlan.

see attached for config.

Thanks!

[Richard Burts]

Yanhyui

I have looked at the config that you posted and do not see any obvious issues that would explain the symptoms that you report. I assume that the router is connected to some switch and wonder if there might be some issue on the switch. Would you post the output of these commands on the switch: show port (for the port connecting to the router), show vlan, and show trunk.

HTH

Rick

[yanhui-wang]

Thanks,Rick,

Actually I hardcoded PC with an IP in data vlan, it works fine and also have spanningtree portfast configured. that is the reason I think this may not be switch issue.

[paul.werner · Accepted solution]

I was looking at your config and I was a little curious about some of the entries you had. For example, I noted this for your DHCP pools:

ip dhcp pool phones

network 10.1.2.0 255.255.255.0

default-router 10.1.2.1

option 150 ip 10.1.3.230

!

ip dhcp pool workstations

network 10.1.1.0 255.255.255.0

default-router 10.1.1.1

This seems to want to allocate all of 10.1.2.1-254 for allocatable IP addresses for the IP phones and 10.1.1.1-254 for the workstations. I then went to your exclution list and found the following:

ip dhcp excluded-address 10.1.2.1 10.1.2.9

ip dhcp excluded-address 10.1.2.101 10.1.2.255

ip dhcp excluded-address 10.1.1.1 10.1.2.49

ip dhcp excluded-address 10.1.1.201 10.1.1.255

I can see the intent behind line 1 (exlude .1 through .9). Likewise on line 2 you reserved from .101 to 255 on the 10.1.2.x subnet for exclusion. What was not clear was line three. Was this intentional?

ip dhcp excluded-address 10.1.1.1 10.1.2.49

Specifically, you ecluded a range that crossed the subnet of the actual pool itself. 10.1.2.49 is on a different subnet. I don't know how the IOS would handle that, other than to *assume* you want to exclude the entire subnet. Try changing that line to this:

ip dhcp excluded-address 10.1.1.1 10.1.1.49

See if that works.

[Richard Burts · Accepted solution]

Paul

I am glad to see you becoming active in these forums. I look forward to more of your insightful analysis.

I believe that this was a good catch on your part. If the third line of the excluded address commands did exclude the entire range of the pool for VLAN 1 then it makes sense that no workstation in VLAN 1 was able to acquire an address. Correcting that line is likely to resolve the problem.

HTH

Rick

[paul.werner]

Rick,

Long time, no see :-) Say hi to the gang from the old days. CCCI was definitely one of the better companies I worked with over the years. Like yourself, I felt the need to stay current on some technologies that got a little rusty. My wife passed me an email that had a CCO newsletter with the networking professionals forum and I noticed a name from the past - yours. I also do miss teaching the classes. Hopefully Netmasters will get back into the teaching arena. I will try to drop in from time to time to make posts where possible. My current job has peaks and valleys and right now there are valleys. Take care, and all the best.

Paul

[yanhui-wang]

Thanks,

You are exactly right!!

It is a typo...