Catalyst 3550 Series; L2 or L3?

Unanswered Question
May 12th, 2008

Hi guys,

I'm not too sure but I have a 48-port Catalyst 3550 Series switch and I need to know if this switch is a Layer 3 switch?

When I do a sh ver, one of the things it says is "Running Layer2/3 Switching Image"

thanks in advance

I have this problem too.
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insccisco Mon, 05/12/2008 - 12:26

I was just reading that. So by enable the "ip routing" I will be basically enabling routing within this switch?

I want to make sure because I will be putting 10 networks in this switch and once I VLAN each of these networks, I want this 3550 to be the default gateway in each of those VLANs.

Let me know if I will be able to accomplish this with this switch?


Jon Marshall Mon, 05/12/2008 - 12:29

Yes you can do this. The 3550 will route between the vlans because they are directly connected.


insccisco Mon, 05/12/2008 - 12:41

good, so I will just setup each VLAN, give them their IP address and then use this IP as the default gateway for all hosts which will belong to those vlans, right?


insccisco Mon, 05/12/2008 - 16:21

you're the greatest.... thank you for the confirmation... I always try to be 300% sure when dealing with cisco as it is quite a big area

I will go ahead and deploy this 3550 switch with all the inter-vlan routing. This is good news as it will free up like 6 physical interfaces that I was using out of my router in order to have routing from all my vlans in 2 2950 switches.

thanks a lot

omal Thu, 05/15/2008 - 08:41


According to my knowledge, usually a 3550 comes in the 'core' layer of the three layer designing model (access layer, distribution layer & core layer) that Cisco describes.

In that it normally says that you fix 2950 switches at Access layer, because it is to access layer that the users connect to.

Then at distribution layer you fix the routers, where inter branch and inter VLAN communication happens at this layer.

Then finally it says at core layer you fix a multi layer (layer 3) switch. The core layer connects to the backbone. A packet goes to the core layer means that it has to go out of the network to the public network.

My question is, if we use a 3550 at the core layer as a L3 switch, how can we connect a leased line or any other WAN connection, I mean to which ports of the switch can we connect them to?

Thanks in advance!

Richard Burts Thu, 05/15/2008 - 09:09


If you think of WAN in terms of leased line then the 3550 does not have an interface that connects to leased line. In that case perhaps the 3550 as the core switch is doing inter vlan routing and could be connected to some router for WAN routing.

And in many networks these days a WAN connection may come on an Ethernet interface, such as DSL or cable modem connections or Metro Ethernet connections. In that case the 3550 could provide connectivity to the WAN without needing any other device.



omal Thu, 05/15/2008 - 09:20

Hi Rick

Thanks a lot for your post. It helps a lot.

I just have one more question. In a 3550 switch that I have, I get 24 Rj45 ports and two some big slots. What are they please?

Thanks in advance!

Richard Burts Thu, 05/15/2008 - 09:42


The two big slots are for GBIC (GigaBit Interface Converter). The GBIC provides flexibility to use copper, fiber, or the GigaStack converters to establish connections.



omal Thu, 05/15/2008 - 09:57


Thanks Rick. Thanks a lot for your information. It helps a lot.

Take care!!

insccisco Thu, 05/15/2008 - 13:35

hey Rick, these GBIC slots are there to link up the switch with another one to make it seem like it is a one unit? right?

Jon Marshall Thu, 05/15/2008 - 13:47

You can use them to interconnect your 3550 switches but they do not appear as one device in the same way that the 3750's appear as one unit.

Edit - apologies i may not have explained that very well. You can cluster 3550 switches to be managed by a single IP address. I just wanted to stress that it is an older technology than the 3750's. For 3550 clustering info see:


insccisco Sun, 05/18/2008 - 19:09

What would be the details on this? I mean on the link.... I know I would have to buy the link adapters, and then configure them. But what about the speed? will the hosts located in sw2 be able to locate the servers at sw1 at the same speed as if those servers were on the same sw as the hosts?



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