More about cisco vlans

[Guest_imported]

Maybe Jsteve or someone could answer till question;

How do I do when i trunk a vlan from a cisco-router to a switch that has vlans set up.
Does this only work with cisco or will it do with other labels as well (for example HP)?

Thanx

 

[DanielBowen]

Do you want to route between those VLANs present on the switch?

Daniel,

 

[wybnormal]

Trunking gets messy between vendors.. What Cisco calls *Trunking* is not the same as what 3Com calls trunkng. Also, ISL is Cisco's own version of a trunking protocol so you really can only trunk 802.1q between vendors. Not to say some do not support ISL, it's just somewhat rare.

In order to trunk a Cisco router ethernet port, there are some requirements

1- IOS level must support it
2- Hardware must support it..
3- The Ethernet port needs to be Fastethernet

So.. no 2500s.. no 1600s, no 1700s even though they have the Fa ports.. the hardware does not support trunking.

2620,2621, 4500 with FastEthernet adapter, 3600s with fastethernet and so on.

In order for this work, you need to config a port on the switch.. assuming 10/100 like A/B on the 1900s or 1-24 on a 2924 to be trunk.. you also need to specify the encapsulation if there is a choice.. the older switches speak only ISL.. some new switches like the 4000 only speaks 802.1q. Decide to have trunking ON, AUTO, DESIRABLE.. if it's going to be a trunk and nothing else, ON works but if the trunk link breaks, the link will go down. AUTO works if the other end asks for it to be trunk. Desirable is good that it will attempt to setup the trunk OR back to a 10/100 port. But, older switches may not understand the protocol it's using to make this choice.

THe router needs to have a fastethernet port config'ed with subinterfaces.. set the encapsulation and like the switch, set the trunk mode to either match the switch ON-ON or something like ON-AUTO, DESIRABLE-AUTO and so on.

I may have missed something since I have not had my coffee yet.. so make sure to read up on it and not take my missive as gospel

MikeS
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"The trouble with giving up civil rights is that you never get them back"

 

[jdavis1]

I've never tried trunking to another vendor's equipment, but wyb is correct in that ISL is a Cisco proprietary protocol and 802.1q is an IEEE standard.

When trunking between a Cisco switch and a Cisco router, you should set up the trunk as "nonegotiate" on the switch, assuming a CatOS switch. This is because the router will not participate in DTP (dynamic trunking protocol). Any setting other than "nonegotiate" will cause the switch send DTP packets on the port, and this is Cisco's recommendation. On an IOS based switch, you will need to enter "switchport trunk encapsulation [dot1q | isl]" and "switchport mode trunk". There are, of course, other parameters you can set like which VLANs are allowed on the trunk.

On the router you need a configuration similar to the following:

interface FastEthernet0/0
no ip address
full-duplex
!
! The following defines the VLAN 1 subinterface
!
interface FastEthernet0/0.1
encapsulation isl 1
ip address 10.1.1.1 255.255.0.0
!
! The following defines the VLAN 3 subinterface
!
interface FastEthernet0/0.3
encapsulation isl 3
ip address 10.3.3.3 255.255.0.0
!

Here's a good link for CatOS:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw5_1/cnfigide/e_trunk.htm

-JD