Re: L3 routing between a 3560 and 3550

jjnagel102 · ‎03-07-2006

I am trying to setup L3 routing between a 3550 in our core to a 3560 in another building on our campus. I have set up the routed ports on both the 3550 and the 3560 and the 3560 can ping other resources on the network such as servers, etc. The problem I am having is that a machine plugged into the 3560 does not get an ip address from the dhcp server. Just wondering what I can do to get this to work. I am new to setting up routing so any help would be appreciated.

Thanks in advance.

Jeff

pkhatri · ‎03-07-2006

Hi Jeff,

Are you using the DHCP server on the 3560 ?

If not, you will need to configure the following under the routed interface for the VLAN that this machine is plugged into:

interface vlan

ip helper-address

That will relay the DHCP packets to the DHCP server so that it can hand out addresses to the client PC.

Hope that helps - pls rate the post if it does.

Paresh

jjnagel102 · ‎03-07-2006

Thanks Paresh,

The 3560 has only one vlan 1 on it right now and I I put in the ip helper-address under vlan 1. The dhcp server is actually on another vlan on the 3550. For some reason the client pc still won't get an ip address.

Thanks.

Jeff

pkhatri · ‎03-07-2006

Hi Jeff,

I assume you have reachability to the DHCP Server from the 3560 - can you ping it from the 3560 at all ?

Paresh

jjnagel102 · ‎03-08-2006

Hi Paresh,

I can ping the DHCP server from the 3560. I have pasted below what I have for the vlan 1 config on the 3560. The strange thing is that I can ping the 172.17.24.1 address but not the 172.17.24.2 address from the 3560.

interface Vlan1

ip address 172.17.24.2 255.255.252.0

ip helper-address 172.16.10.20

no ip redirects

standby 1 ip 172.17.24.1

Thanks for you help.

Jeff

amit-singh · ‎03-07-2006

Hi Jeff,

Let us know that DHCP server is in which Vlan on 3550. As you posted, your 3560 has only vlan 1 that means your clients are on vlan 1 looking for an IP. I would check few things.

1. Try setting up a static IP address on your any client PC and ping the DHCP server to make sure that inter vlan routing is working if DHCP server is in diff Vlan.

2. If that works then make sure that you have the IP helper-address command under the vlan 1 interface on 3550, assuming that 3550 is doing inter vlan routing, if DHCP server is in diff vlan.

3. Check the DHCP pool settings on DHCP server.

Write back if you have an issue.

regards,

-amit singh

nethelper · ‎03-08-2006

Hello,

in addition to all other posts, just make sure that the port where the client is connected to is configured with ´spanning-tree portfast´, otherwise there might be problems with getting IP addresses through DHCP...

Regards,

Nehelper

m.christian · ‎03-08-2006

I agree. I've seen DHCP requests time-out before the switch puts the port in the forwarding state.

jjnagel102 · ‎03-09-2006

Hi,

I set up a static ip address on a client pc and basically the only thing I could ping was the ip address of the routed interface and the ip address of interface vlan 1. From the 3560 I can ping the other vlans off the 3550. I am not sure if this is related but on the 3560 when I did a sh ip int brief the status is up but the protocol is down.

Thanks again for your help.

jjnagel102 · ‎03-10-2006

Hi,

I just want to thank everyone for their help and suggestions. I was able to solve the problem I was having. It turns out that on our core 3550 there was a vlan created in the same network range as the ip that I gave to vlan 1 on the 3560. Once I removed it, everything worked as it should.

Thanks again.

Jeff