Trunking between Cisco 3500XL and 3Com 4800g - Page 2

knichel67 · ‎10-15-2012

I know this is not a 3com support forum, but am hoping that the Cisco GuRu's are watching. I teach the Cisco Network Academy. Our IT Staff recently upgraded the network infrastructure and changed our switches to 3com 4800g's (about 2 years ago).

I want to add a lab bench in my classroom that can access the school's network. My classroom is on a dedicated Cable Modem connection.

Here is my problem...

I am trying to trunk between a 3Com 4800g and a Cisco 3500xl. I can get the a PC that connects to a vlan 1 port on thecisco switch to connect to the 3com switch and get connectivity. However, I cannot get anthing on the cisco switch that is on vlan 2 to connect and get dhcp. I am not a 3com guy, so I am not familiar with the command and configs.

We have 2 vlans on both switches: Vlan 1 is Admin and Vlan 2 is Student.

Our Topology is like this...

Internet -> 3Com 4800g -> Cisco 3500xl

My Cisco 3500xl Fa0/1 is my trunk

interface FastEthernet0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk

The Cisco switch has Vlan 1 interface with appropriate ip in appropriate subnet. I can ping addresses in both vlans from the cisco switch (vlan 1 and vlan 2)

My 3Com 4800g gi1/0/11 is my trunk on other end.

interface GigabitEthernet1/0/11
 port link-type trunk
 port trunk permit vlan 1 to 2
 undo voice vlan mode auto
 broadcast-suppression pps 3000
 undo jumboframe enable
 lldp compliance admin-status cdp txrx

I am connected between them with a crossover cable.

If I plug a pc into the 3500xl to a port in vlan 1, I get DHCP address and connectivity. If I plug into a port in vlan 2, I do not. If I set the pc to have an IP in the vlan 2 subnet, I still have no connectivity. I am guessing there is an issue with the vlan tagging?

This is really bugging me. Any help would be appreciated.

knichel67 · ‎11-26-2012

I aquired another switch that I can play with without issue. If it is not too much trouble, would you give me a config for each (Cisco 3500XL) and (3Comm 4800g) that would allow a pc connected to each switch on vlan 2 to communicate?

I tried to set it up but it is not working.

--

Mike

amikat · ‎11-27-2012

Hi,

It is nice to hear that you have not given up.

So the basic (ie. no dhcp, no voice, no routing etc.) configuration which should enable PC in vlan 2 connected to each switch to communicate is as follows (we will stick with the same trunk port and addressing scheme):

3500XL (PC at port fa0/2, trunk to 4800G port fa0/1):

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

interface FastEthernet0/2

switchport access vlan 2

Interface Vlan 1

no ip address

shutdown

interface VLAN2

ip address 192.168.140.108 255.255.254.0

no shutdown

4800G (PC at port gi1/0/1, trunk to 3500XL port gi 1/0/11):

vlan 1 to 2

interface Vlan-interface2

ip address 192.168.140.109 255.255.254.0

interface GigabitEthernet1/0/1

port link-type access

port access vlan 2

interface GigabitEthernet1/0/11

port link-type trunk

port trunk permit vlan 1 to 2

As you can see I have also included Interface Vlan 2 configuration which should give you the option to ping to these from both sides. Please be sure to assign the correct ip addresses and subnet masks to your PCs (you do not need DG at the moment).

As soon as you succeed to connect PCs at both sides we can extend the configuration similarly to your production network.

Good luck!

Best regards,

Antonin

knichel67 · ‎11-27-2012

I appreciate the assistance very much. I have aquired an additional switch to play with and wiped it as well as the cisco switch. I applied the config and everything is working.

It seems that the issue was with how they were handling vlan 2 on the 3comm as untagged where on the cisco it was tagged. I tried to set vlan 2 as native originally on the cisco but that did not do the trick.

So it works now.

Thanks a million.

Mike