Trunking and DHCP

[mattb]

I have two NetVanta 1335, one is set up as a router and has 3 VLANs,  101, 102, 103.

The second one is set up just as a switch, and also has the same VLANs.

The Gigabit 0/2's are connected together and trunking is configured.

My DHCP server is a linux PC and is connected to both 102 and 103 via two different NIC's to the router 1335.

Connecting a PC to the router on any of the ports configured for VLAN 102 or 103, the PC is able to get an IP.

However, if I connect the PC to the 1335 switch, on either VLAN, it cannot get an address.

Hope this is making sense...

router <-Gig trunk -> switch

        I  <- Linux PC x2 (two ports, one on each VLAN)

Both Gig ports are configured:

interface gigabit-switchport 0/2

  description Uplink to Bridge (primary)

  spanning-tree edgeport

  no shutdown

  switchport mode trunk

  switchport trunk native vlan 102

And the other ports are configured:

interface switchport 0/8

  spanning-tree edgeport

  no shutdown

  switchport access vlan 102      (or 103)

[Anonymous]

- Everything that I have seen appears to be correct. Could you post the configurations of both 1335s? Remember to edit any information that is sensitive to your network. Also, which ports is the DHCP server plugging into and which two ports did you plug the PCs into?

Thanks,

Noor

[mattb]

Thanks for the reply.   Attached are the configs.    DHCP server is connected to ports 1-2-3 on the router.  Should be giving out DHCP addresses on ports 2 and 3.

I cut out a lot of the repeating info on the other ports.

Just to be clear, DHCP works fine when connected to the router, but only VLAN 102 works when connected to the bridge (Switchport 0/1 works fine, switchport 0/2 does not).

[Anonymous]

- Thanks for posting that information. As I understand, DHCP works on the 'routing' 1335 for VLANs 102 and 103. However, DHCP only works on VLAN 102 when you plug into the 'switching' 1335. I'm assuiming that VLAN 103 on the 'switching' 1335 is never able to obtain an IP address at all.

I would try setting the spanning-tree mode on the access ports of the 'switching' 1335 to "spanning-tree edgeport". It could be that the Linux PC is not waiting for spanning-tree to converge when the access port comes up and, therefore, is timing out before the port has a chance to come up into the forwarding state. By setting the access port to edgeport, the port will immediately go into the forwarding state without having to go through the spanning-tree calculations.

Edgeport can be enabled in the CLI by going into the port configuration menu and issuing the "spanning-tree edgeport" command. This can also be done in the Web GUI by navigating to Data->Switch->Ports, then clicking on the port you would like to modify. On the port configuration page, you will want to 'check' the 'Edgeport Mode' option and click 'Apply'.

Please do not hesitate to let us know if you have any questions.

Thanks,

Noor

[mattb]

For practical purposed, I'm going to call the 1335 in routing mode "Router" and the other 1335 "Switch"

I did try changing the ports to spanning tree edge port mode, which is the default mode.

It's not just the linux PC that cannot get an IP.   I tried other laptops as well.

On the linux machine, I'll wait until the port goes into forwarding mode, then issue a dhcp renew on the client and it still cannot come up with an IP on the 103 network.

It works if I connect the same machine to the 1335 that is routing (and the DHCP Server is attached to).

This really appears that the DHCP broadcast is not going across the trunk between the two 1335's.

On another subject, if you notice, I have gvrp enabled on the router, but if I enable it on the switch, it really bogs the network down.  Even CLI commands take 3-4 seconds to respond. Do I need to remove the identical VLANs on the switch before enabling?  (other switches do the same thing as well).

[Anonymous]

- There are a couple of things I was hoping you could try to help pinpoint where the issue may be:

1. Give the PC connected to the "Switch" on vlan 103 a static IP address and see if you are able to ping across the trunk (i.e the VLAN IP address of VLANs 102 and 103)

2. Set the PC back to retrieve its IP via DHCP and get a packet capture from the PC as well as the DHCP server at the same time.

3. Try setting the "Router" to be the DHCP server for VLAN 103. Capture the output to "debug ip dhcp-server" as well as a packet capture of the PC.

The following article gives instructions on how to set up a port-mirror on NetVanta switches:

As far as GVRP goes, it is not actually doing anything with your current configuration since you have the VLANs statically defined on both the "router" and "switch". Also, I do not believe GVRP is necessary at this point due to the fact that you will need to statically define the VLANs on both 1335s regardless. So, in fact, I would recommend disabling GVRP at this time.

Please do not hesitate to let us know if you have any questions.

Thanks,

Noor

[mattb]

1 - Static IP works just fine.

I'll do the packet capture at some point here.  I'll want to be near the gear while making changes, just in case something goes wrong.

[Anonymous]

- Are you still having trouble with this setup? Please do not hesitate to let us know if you have any questions.

Thanks,

Noor

[Anonymous]

:

I went ahead and flagged this post as “Assumed Answered.”  If any of the responses on this thread assisted you, please mark them as either Correct or Helpful answers with the applicable buttons.  This will make them visible and help other members of the community find solutions more easily.  If you still need assistance, I would be more than happy to continue working with you on this - just let me know in a reply.

Levi