Recently we’ve obtained a bunch of 3Com 4500G 48 port switches, and we’d like to be able to manage them slightly more effectively instead of leaving them as dumb switches. However, rather than giving each switch an IP address, 3Com allows you to use HGMPv2 to cluster them all under one IP address.

Now, this may seem fairly trivial to those with separate management networks, but sadly we’re not in that position (yet) to have a separate management network. Even if we were to set up a new VLAN for management purposes, it wouldn’t be accessible to the rest of the network staff external to our office. So, as it stands, the cluster management switch still has to use VLAN 1 for the admin and management stuff. It can still use (and has to use) a different RFC1918 address for the internal clustering network, but that’s all transparent to us.

Below is a short detail of what needs done in order to build a cluster of 4500G switches…

Enabling the electrical (Cat5) Dual combo port

As the dual combo SFP port is shared with ports 23, 24, 47 and 48 (49, 50, 51, and 52 respectively), the relevant port must be brought up (or ‘undo shutdown’ on its counterpart), in order to enable it.

[WMSWC1_0.WMSW001]system-view
System View: return to User View with Ctrl+Z.
[WMSWC1_0.WMSW001]interface GigabitEthernet 1/0/51
[WMSWC1_0.WMSW001-GigabitEthernet1/0/51]undo shutdown
[WMSWC1_0.WMSW001-GigabitEthernet1/0/51]interface GigabitEthernet 1/0/52
[WMSWC1_0.WMSW001-GigabitEthernet1/0/52]undo shutdown
[WMSWC1_0.WMSW001-GigabitEthernet1/0/52]quit
[WMSWC1_0.WMSW001]

This will enable combo ports 51 and 52, and leave 47 and 48 shut down.

Initial setup

This is done on the switch that you want to be the management switch.

Globally enable Neighbour Discovery Protocol. This allows the switches to discover information about connected neighbours, such as firmware versions, mac addresses, link states, etc.
ndp enable
Globall enable Neighbour Topology Discovery Protocol. This allows the switches to collect information regarding the topology of the network, connected devices, etc
ntdp enable
All NDP packets have a holdtime variable set. This is how long the recieving device will store the information for. The next setting defines how long that should be.
ndp timer aging 200
Next, set how often the ndp packets should be transmitted.
ndp timer hello 70
The number of hops in which to collect topology information. I’ve set this to 10, as we had 9 switches that were daisy chained for a while. Far from optimal, and now in a more star like topology anyway.
ntdp hop 10
Set the delays for each device, and port, respectively
ntdp timer hop-delay 150
ntdp timer port-delay 15
Define the period, in minutes, between topology information collections.
ntdp timer 3
Enable cluster mode.
cluster enable
…and switch into cluster view
cluster
The cluster requires an independant RFC1918 address range to work with. This is for internal management purposes and never seen by the outside world. Apparently.
ip-pool 172.16.0.1 255.255.255.0
Tell the system to build the cluster
build WMSWC1
Configure the length of time to hold member information for, before deciding that the member is gone, and define how long between handshake packets
holdtime 100
timer 10

Adding a cluster member

Just enable the following options on member devices

ndp enable
ntdp enable
cluster enable

On management device
Switch into cluster view again, and add the remote device.
cluster
add-member 3 mac-address 0022-5726-d080

Repeat the above add-member command for each member number (the first parameter) with the MAC address of each switch. After you’re done, all the switches except for the cluster commander should display ‘S’ for ‘Slave’ on their LCD display. The Cluster Commander displays a ‘C’ instead.

Once everything is up and running, you can then use topology accept all and topology save-to local-flash to accept and save the current topology layout.

It should also be noted that there is a cluster autobuild feature, but it’s always best to at least have a rough idea of how it works