ISL and DOT1q

gojericho0gojericho0 Member Posts: 1,059 ■■■□□□□□□□
in CCNA & CCENT
Is there an advantage/disadvantage of the methods (enclapsalation/first 4 bytes) of packaging the info on the frame for VLAN identification?
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  • lordylordy Member Posts: 632 ■■■■□□□□□□
    ISL is Cisco proprietary.
    dot1q is an IEEE standard.

    As ISL offers no real advantages that I am aware of I prefer dot1q.
    Linux also speaks dot1q so that's pretty neat.
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  • johnnynodoughjohnnynodough Member Posts: 634
    ISL doesnt recognize the native VLAn either, so doesnt play nice with IP phones. ISL completely encapsulates the packets. If a packet is destined for the native VLAN on a dot1q network, the switch wont even tag the frame.
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  • gojericho0gojericho0 Member Posts: 1,059 ■■■□□□□□□□
    Since dot1q seems much more friendly why doesn't everyone use that?
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  • johnnynodoughjohnnynodough Member Posts: 634
    They pretty much do, the newer switches dont support ISL.
    Go Hawks - 7 and 2

    2 games againts San Fran coming up, oh yeah baby, why even play? just put then in the win category and call it good :p
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  • lordylordy Member Posts: 632 ■■■■□□□□□□
    Yep, ISL seems to slowly go down the drain.

    I have heard that it isn't supported in the newer IOS so people will sooner or later switch.
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  • AceAllAceAll Member Posts: 36 ■■□□□□□□□□
    I heard the same. I think ISL is not supported by the latest 2950 switches which uses IOS 12.0 or higher
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  • wildfirewildfire Member Posts: 654
    ISL isnt support in any of the 2950 switches.

    From a home lab perspective, you no longer need a fast ethernet interface to support 802.1Q Encap, since IOS 12.2 the standard interface on Cisco 2610-12 supports 802.1Q

    http://www.cisco.com/en/US/products/hw/routers/ps259/prod_bulletin09186a00800921e4.html

    ISL is hardly covered in the latest series of exams. Although there still may be a Question or two on it.
    Looking for CCIE lab study partnerts, in the UK or Online.
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