Trunking protocol in Cat2950?

[imran_mcse]

I just want to know that why there is only 802.IQ Trunking support in Cat2950.

Why not ISL, Is it true that 802.IQ is better than ISL,

Why Cisco left ISL in 2950.

Pls explain.

[Kevin Dorrell]

ISL was a Cisco-proprietary solution, that was implemented before the 802.1Q standard. It is gradually being phased out, and quite a lot of recent equipment supports 802.1Q only. The ISL frame is considerably bigger than an 802.1Q, and requires quite a lot more processing. 802.1Q is therefore much better suited to implementation in hardware than is ISL.

Kevin Dorrell

Luxembourg

[imran_mcse]

hi kevin,

You mean that ISL is totally not available in Cat2950 Switches. If your answer is Yes.

Then when we use command "show Vlan", then it displays ISL ID something like this, so what is this,

How can we check that our vlans are using what trunking protocol.

Plz help.

[Kevin Dorrell]

That's right. ISL is not avaiable in any 2950 series due to hardware limitations, amongst other reasons.

You are right, I think I have seen a reference to ISL in one of the show commands, but I think it is a spurious hangover from the 2900XL code. I couldn't find it on my 2950 switches, but I think I remember seeing it on a posting on this forum. As I say, I'm pretty sure it is spurious. What was the exact show command you were using, and which IOS do you have. Could you post the output so we can compare with what I have here?

Kevin Dorrell

Luxembourg

[Josef Oduwo]

The Catalyst 2950 switches do not support Inter-Switch Link Protocol (ISL) trunking due to hardware limitations (http://www.cisco.com/en/US/products/hw/switches/ps628/products_configuration_example09186a00800ef797.shtml).

801.Q is an IEEE standard (http://standards.ieee.org/getieee802/download/802.1Q-2003.pdf) and by default has a wider acceptance than the Cisco-proprietary ISL (http://www.cisco.com/warp/public/473/24.shtml). There is a fine illustration of the differences between the two tagging formats here http://www.cisco.com/en/US/tech/tk389/tk390/technologies_tech_note09186a0080094665.shtml.

Josef.

[robphill]

It is my understanding that on top of hardware limitations that prevent the 2950 from supporting ISL, Cisco in general is doing away with ISL. One reason I have heard is that since ISL tags all packets and does not support "native VLAN" which is vital for VoIP apps they are doing away with ISL to facilitate VoIP in the future.