VLANS

[BZeto]

Are VLANS widely used in current networks?
Also, is vlan administration done entirely through the switch interface? Do IP addresses matter at all in a VLAN?

Just some things that were never clear to me.

Thanks

 

[Woodie]

Yes.
I dunno. I believe so, but it depends on the switch manufacturer.
Yes.

 

[spidey07]

Originally posted by: BZeto
Are VLANS widely used in current networks?
Also, is vlan administration done entirely through the switch interface? Do IP addresses matter at all in a VLAN?

Just some things that were never clear to me.

Thanks

Are vlans used widely?
Not as much as they used to be. They're still used, but current design practices dictate that a vlan be contained to a single network closet and ONLY that closet. So it's not like the old design models where vlans were used everywhere.

Vlan administration is done on the switch itself.

IP addresses matter a lot to a VLAN. A vlan is a layer2 network and a single broadcast domain. There is another term for that - a subnetwork or LAN. each vlan typically contains an IP network/subnet so they are addressed differently.

 

[BZeto]

Thanks for the answers.

One thing though, if each vlan is on a different subnet, what is used to route between vlans? I thought you needed routers for that.

 

[spidey07]

lol, yeah.

that's what routers do.

They route.



But normally the routing is done by a switch (aka layer 3 switch, or more simply a router)

 

[cmetz]

spidey07, a lot of medium sized enterprises use L2-only switches slaving off of one L3 switch, and carry VLAN trunks between them. The downside is that you route between VLAN x and VLAN y on an L2 switch by going up to the L3 switch and back, but if your traffic levels are low and it's a gigabit link, it's very cost effective. So I wouldn't quite agree with your statement about VLANs only within a closet. I see a lot of folks who use them building-wide.

 

[jlazzaro]

Originally posted by: cmetz
spidey07, a lot of medium sized enterprises use L2-only switches slaving off of one L3 switch, and carry VLAN trunks between them. The downside is that you route between VLAN x and VLAN y on an L2 switch by going up to the L3 switch and back, but if your traffic levels are low and it's a gigabit link, it's very cost effective. So I wouldn't quite agree with your statement about VLANs only within a closet. I see a lot of folks who use them building-wide.

This was the exact setup of a network I used to work on...all cisco layer 2's using default vlan connected to layer 3 extreme switches that had all the vlan info based on the interface with 10gigabit links between the layer 3's just curious, where did you get that from spidey?

 

[spidey07]

It's called the 3-tier design model or mulitlayer design.

Pretty much what you and cmetz are talking about. Each access layer switch/closet contain a single vlan (unless your doing voice, then 2), and then the distribution layer does layer3 only. Typically the distribution and core layers have two or more layer3 switches for redundancy.

I guess what I meant was VLANs aren't trunked all over the place like they used to be in "flat" networks. If this is done a problem in one closet/building can cause problems for any other switch that has that VLAN.