HiddenOne

The first thing I would like to do is clarify that this article discusses how to configure an 802.1q VLAN trunk between a Cisco switch and an HP Procurve switch. From here on out any references to trunking refer to an 802.1q tagged VLAN trunk. I am making that distinction now because in the Procurve world trunking refers to a feature similar to Cisco’s Etherchannel.

In a mixed vendor network, consisting of both Cisco and HP Procurve switches, it is important to keep traffic to and from multiple VLANs flowing. In any environment trunks, or tagged VLAN links, are an integral part of keeping that traffic moving. This can be a source of confusion since Cisco and HP handle the tagging of VLANs a bit differently. In my opinion Cisco handles 802.1q trunks in an easier to manage way; however the method used by Procurve switches is simple once you are familiar with the process.

The trunk between a Cisco and HP Procurve switch must be of the 802.1q variety. ISL trunks will not work because it is a Cisco proprietary encapsulation. I rarely see ISL in use these days, and I personally consider 802.1q the preferred method of encapsulation if for no other reason than its interoperability.

I will focus on the configuration of the trunks on each switch; if you need a refresher on how to configure VLANs on Cisco or Procurve switches consult the documentation for your switches. Once you have configured all of the needed VLANs it is time to configure the trunk on the Cisco switch using the following commands:

3550-02(config)#interface fa0/48
3550-02(config-if)#switchport mode trunk
3550-02(config-if)#switchport trunk allowed vlan all
3550-02(config-if)#no shutdown
3550-02(config-if)#exit

Here interface number 48 is the trunk port on the Cisco switch. After entering interface sub-configuration mode, the port mode is changed to “trunk” (the default is access). Next, it’s a good idea to set what VLANs you want to allow across the trunk. Here I used the “all” option, but for security reasons you may wish to specifically list the VLANs you use in your environment. Finally, you want to make sure the interface is not in a shutdown state because that would not allow the traffic to flow (ask me how I know)!

Procurve switches, much like their Cisco counterparts, can have a VLAN either tagged or untagged on any particular port. The configuration of this tagging varies a bit as shown in the configuration below.

HP ProCurve Switch 3400cl-24G(config)# vlan 4
HP ProCurve Switch 3400cl-24G(vlan-4)# tagged 24
HP ProCurve Switch 3400cl-24G(vlan-4)# exit

The “vlan 4” command drops you into VLAN sub-configuration mode. Here the “tagged 24” command is used to tell the switch to encapsulate any packets on port 24 that originate from VLAN 4. As may already be obvious, port 24 will be the trunk port on the HP switch. Below is the command that is used to accomplish the same for VLAN 5.

HP ProCurve Switch 3400cl-24G(config)# vlan 5
HP ProCurve Switch 3400cl-24G(vlan-5)# tagged 24
HP ProCurve Switch 3400cl-24G(vlan-5)# exit

The next step is to connect the trunk ports on each switch using the appropriate network cable. Issue the “show interfaces fa0/48 trunk” command on the Cisco switch to verify the trunk has been established. You should see output similar to what is displayed below.

3550-02#show interfaces fa0/48 trunk

Port        Mode             Encapsulation  Status        Native vlan
Fa0/48      on               802.1q                trunking   1

Port            Vlans allowed on trunk
Fa0/48      1-4094

Port            Vlans allowed and active in management domain
Fa0/48      1,4-5

Port            Vlans in spanning tree forwarding state and not pruned
Fa0/48      1,4-5

The key here is that you want the status to read “trunking”. This will indicate that the trunk has been successfully established.

Next test connectivity between two hosts that are in the same VLAN, but on different switches. In this case I assigned IP addresses directly to the VLAN interface on each switch. Here is the IP address layout I used.

Cisco 3550

• VLAN 4: 172.16.1.1/24
• VLAN 5: 172.16.2.1/24

HP 3400

• VLAN 4: 172.16.1.2/24
• VLAN 5: 172.16.2.2/24

Below is ping output from the Cisco switch  after issuing a ping command to both VLAN interfaces on the HP switch:

3550-02#ping 172.16.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

3550-02#ping 172.16.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/202/1000 ms

Now, here is the ping output from the HP switch after issuing a ping command to both of the VLAN interfaces on the Cisco switch.

HP ProCurve Switch 3400cl-24G# ping 172.16.1.1
172.16.1.1 is alive, time = 1 ms

HP ProCurve Switch 3400cl-24G# ping 172.16.2.1
172.16.2.1 is alive, time = 1 ms

As you can see, configuration of 802.1q trunks between Cisco and HP Procurve switches is not overly complicated. The key is to test connectivity to ensure that traffic is flowing as it should. In larger environments it could be a bit cumbersome to manage a large number of tagged VLANs on a Procurve switch. If things are not working, double check your config on both ends. Many times I find that it is easy to forget a tagged command on the HP side of things.