RE: [nsp] ISL and 802.1q trunk

From: Oleg Kostine (okostine@chello.com)
Date: Wed Sep 20 2000 - 07:11:30 EDT


One little detail:
If you use 802.1q on Cisco you have only one STP domain for all vlans over
the trunk.
29xx,35xx or 6x00 manuals is a good source for more info.

-----Original Message-----
From: Dmitri Kalintsev [mailto:dek@hades.uz]
Sent: 20 September 2000 12:57
To: cisco-nsp@puck.nether.net
Subject: Re: [nsp] ISL and 802.1q trunk

On Wed, Sep 20, 2000 at 06:07:48PM +0800, Cho Man Fai wrote:
>
> Dear all,
>
> Can ISL and 802.1q trunk exist in the same network? Any workaround to do

Sure they can. One little detail - if you run VLANs with numbers higher than
1000 when you use 802.1q, you'll have to manually map them into lower
numbers
when you need them to cross ISL trunk.

> so without changing the whole network to 802.1q? What's the pros and cons
> of the two trunking protocol?

802.1q is an industry standard, though not all cisco catalysts support it.
802.1q will support up to 4096 VLANs, where ISL will support only 1024 (or
1000? correct me if I'm wrong). ISL does not really care about "native VLAN"
for trunk port, 802.1q does - it must match on both sides of the trunk or
you'll get lost packets.

In general, the answer probably is "use 802.1q where you can, and ISL where
you must".

SY,

-- 
   CCNP,CCDP (R&S)                                   Dmitri E. Kalintsev
   CDPlayer@irc          Chief of Network Operations @ Sonorous Networks
   dek @ hades.uz                   phone: +27 11-327-1524 fax: 327-7648
   http://hades.uz                    UIN:7150410  cell  +27 82-336-1033



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