I am just learning on a 2948G managed switch. I have 48 ports and I would like to divide those up into 4 networks with 12 ports each. I don't want them to be able to communicate between networks at all as a security measure.

I know I have a lot of questions and I have tried to read and understand these on my own. I have put the more important questions at the top if you can answer any of them I would appreciate it!

I am trying to understand the difference between VLAN and trunking and etherchannel and which one would do what I am trying to do above. It sounds like VLAN might be it, but isn't that about the same as just letting the connected devices assign static IPs in the same range? Or does setting it up as a VLAN ensure that none of the devices try to change their IP to connect to another port in another subnet that I don't want it to access?

Does trunking in effect connect those separate networks? For instance, if network A has ports 1-12 and network B 13-24, would port 3 and 18 still be able to communicate with trunking on?

Also I'm not sure if there are specific groups of ports that would make traffic move more smoothly. Eg) is there one central hub in the back of the switch that all data going form port 1->2 and also 1->48 will pass through? Or can 1 communicate with 2 without interfering with data from 47 to 48? Or when the ports are all in module 1, does that mean the module itself has a central hub that all data will pass through?

2 Answers 2


What you are trying to achieve is done with VLANs. A VLAN is basically a logical L2 domain so two hosts on the same VLAN will be able to communicate without a router.

Trunking basically means 'allow more than one VLAN on the same port'. You can do that to allow a host to be able to connect to different VLANs using the same port or for interswitch communications. If you have two switches you will want to connect them with a trunk so the hosts in VLAN A on SW1 can communicate with hosts in VLAN A on SW2.

Etherchannel is used to aggregate two ports into one logical port adding the bandwidth.

About the architecture of this specific hardware I am not sure. Usually ports are connected by groups. Ports 1-8 belong to the same ASIC, so port 2 to get to port 9 (which is in a different ASIC) will have to go through the backplane. However, from port 1 to port 2 you do not need to get to the backplane. However, this is very platform specific so read the switch architecture to be sure about this.


  • Awesome thanks - i think i understand the terminology and process a little better now to make sense of everything :)
    – DAB
    Commented Jul 20, 2013 at 21:58

Vlans will allow you to have 4 networks that do not talk to each other without (usually) going though a L3 devices. You need 1 IP address space per VLAN

If you want a single connection to the L3 device you use trunking, that allows the 4 vlans to use a single wire (don't forget you need to reserve an uplink port for this.

Etherchannel allows multiple links to look like 1 link to spanning tree, so if 1 link fails traffic just flows.

As to internal hardware, does not matter in 99% of the cases on low end hardware, there are some platforms that only allow etherchannels on the same parts of the switch.

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