ISL and DOT1.Q

Unanswered Question
Nagaraja Thanthry Tue, 09/21/2010 - 14:45

Hello,


You can use a mix of DOT1q or ISL trunks in the switch (except on some where ISL is not supported).


Regards,


NT

Reza Sharifi Tue, 09/21/2010 - 14:58

Hi Abbas,


In addition to NT's comments, here are some of the 6500 modules that do not support ISL:


When configuring Layer 2 LAN ports, follow these guidelines and restrictions:

The following switching modules do not support ISL encapsulation:

WS-X6502-10GE

WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF

WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF


http://scc.cisco.com/en/US/docs/routers/7600/ios/12.2SXF/configuration/guide/layer2.html


HTH

Reza

Leo Laohoo Tue, 09/21/2010 - 15:05

Addition to what was posted, the following model DO NOT support ISL:


2940/2950/2955, 2960/2960S


NOTE:


1900 will support ONLY ISL

Scott_O'Brien Tue, 09/21/2010 - 17:10

to also add to this remember:


isl does not use a native vlan

if one side isl and the other is dot 1q the link will work you just will get native vlan miss matches on the dot1q side and also may course baby giant frames.

Jon Marshall Wed, 09/22/2010 - 02:24

Scott_O'Brien wrote:


to also add to this remember:


isl does not use a native vlan

if one side isl and the other is dot 1q the link will work you just will get native vlan miss matches on the dot1q side and also may course baby giant frames.


Scott


A switch can use a mixture of 802.1q and ISL encapsulations on trunk links but a trunk link between 2 switches must be the same encapsulation as ISL and 802.1q use very different methods when they add a vlan tag ie.


802.1q inserts a tag into the existing frame

ISL actually encapsulates the frame with a new header


so the 2 switches must agree on the encapsulation being used per trunk link otherwise they will be looking for the vlan information in the wrong place.


Jon

Leo Laohoo Wed, 09/22/2010 - 15:16

Aside from what Jon's mentioned (+5), be aware that not all brand will support ISL.

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