Routing Mystery - where is it going?

[bleucube]

I have a mystery and before I call Leonard Nimoy in to do a "In Search Of...." episode thought I post here.

PROBLEM:

I'm converting a remote site from ISDN (At the moment using Ascend Pipelines) and converting the site to Point-to-point using a 1760 Cisco on the remote end and a 7204 vxr on the other. After conversion, everything works except DHCPOFFER doesn't hit the workstation. EVERYTHING works except that. Ping/Telent/Http..blahblah. I can see DHCPDISCOVER packet hit the DHCP server, I can see the DHCP server sending a DHCPOFFER but workstation doesn't get it. If I put a different IP subnet for this location the offer goes through. Routing problem right?

SETUP:

[workstation] - IP 172.22.36.7

|

[1706 Cisco] - E0=172.22.36.1 S0=172.22.136.1 (ip helper on E0)

|

[7204 VXR Cisco] - S0=172.22.136.2 E0=172.22.1.8 (Ip helper on E0)

|

[2948G-L3 Cisco] - 172.22.1.1

|

[DHCP Server] - 172.22.1.50

TROUBLESHOOTING THUS FAR:

1. Check routes on all routers/servers/workstations

2. Clear routers on everything. We are using EIGRP.

3. Enable Show Debug on all routers

with this I see the DHCPDISCOVER hit everything,

I don't see an DHCPOFFER hit the 172.22.1.1 on the way back

4. Put a Sniffer on DHCP server and on the Workstation ends

- Sniffer shows its heading to the right place

5. Enable DHCP debug on the server, shows everything is fine except it can't send DHCPOFFER.

6. If I go to a workstation after converting the site, and it still has an IP, the dhcpserver can ping the workstation no problem. Once I release the IP it can't get another one.

7. I have 7 total sites, 4 sites are working - three are not, using the exact same config, except different ips.

8. I removed all sites from the 7200VXR and cleared all routes and then attempt switch over but still had problem. I was thinking something was advertising the wrong route.

SUGGESTIONS?

I know I can get it to work if I change the IP subnet. Really don't want to do this, need to figure out issue, who knows when and where it will rear its ugly head.

Any help will be great!

[namso2]

It looks like a DHCP server configuation problem. Windows clients don't respond to BOOTP offers, only DHCP. Make sure the scope for that subnet is configured for DHCP/BOOTP or DCHP only.

[bleucube]

As much as the finger points to DHCP, I don't think it is. The reason why I say this:

1. Had a couple people check the different subnet's and everyone is configured the same.

2. In the subnet I'm having a problem with, If I just change the subnet pool - it works.

The Range Type is set to Dynamic Bootp and DHCP

[msingla]

Thanx for the inf,Iam trying and others too.I am also discusiing the same problem with many people on other groups.If anybody comes out of solution.

[bleucube]

Well, Friday is almost over. Tomorrow me and another Administrator will be SOLVING this, one way or another. I will post the outcome.

Here's is are plan... pretty sketchy but you can probably tell we tried just about everything we can think of...

(Currently RIP is being use on 172.22.1.1 because of the ISDN routers, after today we will not need RIP)

Plan A

Backup Configuration on 172.22.1.1

Remove RIP from 172.22.1.1

Clear all routes

Try Out T1

Plan B

Unplug all remote sites

clear all routes

Try out T1

.......

Plan Z

Change the IP Subnet

Change IP on server

Change IP on printers

Change IP on E0 of both routers 1760 and 7204

Clear all routes

Try out T1

Test everything to see what we broke

See the bad thing about Plan Z, is I know it will fix the issue... whatever that maybe. Who know tho, something else might come up and bite us down the road.

[deilert]

I do not see the segment for your next hop 172.22.1.1 in your default route in the 7206 config what segment is it on ?

[bleucube]

The 7204 VXR is on the same segment as 172.22.1.1

[workstation] - IP 172.22.36.7

|

[1706 Cisco] - E0=172.22.36.1 S0=172.22.136.1 (ip helper on E0)

| Default route is 0.0.0.0.0 255.255.255.255 172.22.136.2

|

[7204 VXR Cisco] - S0=172.22.136.2 E0=172.22.1.8

| Default route is 0.0.0.0 255.255.255.255 172.22.1.1

|

[2948G-L3 Cisco] - 172.22.1.1

|

[DHCP Server] - 172.22.1.50

[bleucube]

Well Saturday went really well. Wanted to update and close this conversation. I really don't have a defined idea on what was screwing up the routes, but this is what I did.

1. I listened to the traffic again and tracked down all the RIP packets. Found:

a) A couple of Lanrover's using RIP that had old routes. I removed RIP and cleared out the routes. These devices do not need to know about the network, they only need to know about the core router 172.22.1.1

b) I disconnect the three remain ISDN lines from the core router 172.22.1.1

c) I removed RIP from the core router 172.22.1.1, and cleared all routes

2. Went onsite and converted it and everything went great! DHCPOFFER from DHCP made it to the workstation and the Workstation sent back a DHCPACK. Just to test it we excluded the IP the workstation receieved, released all and renewed... sure enough got another IP!!! Yeah. All three took.

So now have all the sites on T1's. I can only surmise something was sending the old routes out.

On a side note, we had one site that couldn't telnet to our Unix service box, found out our unix had old routes defined on it too.

So check yer routes.

Thanks everyone for all your help, and I hope this can help others with same issue.