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Switching vs. Trunking

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by swetbak

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Can anyone tell me the difference between "switching" and "trunking" in reguards to connecting switches together. Any examples to use each would help. I've read some things, but still don't think I have a good handle on it.

6 replies

by simon park

Am I right in saying this is to link actives together?

trunking is when you use 2 (or more) ports to create a fast backbone between units - in my case I link 3com 3300 100mb switches via a matrix cable to get gig backbone then link remaining switches into these via 2 ports on a trunk giving 200mb link (400 duplex) to the remaining switches. The alternative is to crossover on a port at 100mb?

Is this what you mean or should I go back to sleep?

by swetbak

Thanks for responding Simon,

I meant to ask the difference between "stacking" and "trunking", not "switching". I have four 3com16670 switches. Two of them are "stacked" with a thick data cable(is this the matrix cable of which you speak?) from behind, these two are linked with the other two only by a single crossover cable. Seems to me they should all be "stacked" together. It's just a single network. All those switches are 10Mb. We just got a couple 10/100Mb switches that we want tolink into the network. They don't have "stacking" capability, but they do have "trunking". Would I connect the new switches to the old 3com's via the trunking ports to increase the throughtput between the segments. Does this do the same thing as "stacking" the switches?

by vrojasg

Switching is the term used when we refer to the 3 basic functions of "Transparent bridging". Learning, filtering and forwarding (sometimes a fourth function is added, "Loop Avoidance"). Basically, switching makes possible a dedicated point-to-point connection between two devices in a LAN environment. When the switch receives a frame from a port, it learns the MAC address and builds a MAC Table with ports vs. MAC addresses.

Trunking refers to a feature where is possible to pass traffic from different VLANs into a single link connecting two switches. The function of multiplexing makes this possible. In order to identify the source VLAN, two types of encapsulation methods can be used (ISL and Dot1q).

by remistuff

Assuming you know what a switch is, trunking is a term used in association with the features of a switch namely VLAN's. A VLAN is basically a logical (as opposed to physical) segmentation of your network based on switch ports. In other words, if youhave Switches A,B and C each with 12 ports, you can assign the first 6 ports in each switch to "VLAN 1" and the next six to VLAN "2" (assuming VLAN 1 & 2 are your VLAN of choice). Now, in other for VLAN 1 on "switch A" to communicate with VLAN 1 on switch 2 or 3, each Switch MUST have a port designated as a TRUNK port. As such a trunk port by definition carries multiple VLAN's. Think of it as a port on a switch that allows all other ports on the switch to pass information through it in VLAN environment.

by simon park

if they are stacked then if they behave like the 100mb switches they become in effect larger switches (eg if I chain 2 x 24 port 3300's via a matrix lead then I get 48 ports on the switch or I can seperate them but then what's the point? This give me a gigbit backbone for all 48 port?? You dont need to run VLANS to trunk and unless you are familiar with VLAN avoid it. If you are running 10mb its probably easier to upgrade. VLANS are great but need to be setup correctly.

by swetbak

I don't think I will fully understand the VLAN concept using the "trunking" feature without actually setting one up.
I did however use the "trunking" feature to V-STACK (if you will allow me to coin the term) the three switches together. Not a gigabit link between them, but better than linking thru a single port.

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