ISL and dot1q?

mikearamamikearama Member Posts: 749
in CCNA & CCENT
I can't find an answer online...

Could a single switch (say, 3750) have an ISL trunk to another cisco device, but another trunk using dot1q to, say, a Baystack?

or does the first trunk encap dictate all future trunk encaps?

Thanks,
mike
There are only 10 kinds of people... those who understand binary, and those that don't.

CCIE Studies: Written passed: Jan 21/12 Lab Prep: Hours reading: 385. Hours labbing: 110

Taking a time-out to add the CCVP. Capitalizing on a current IPT pilot project.
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Comments

  • networker050184networker050184 Mod Posts: 11,962 Mod
    Yes a switch can use both ISL and dot1q on different trunks. ISL only supports VLANs 1 - 1001 and dot1q supports 0 - 4094 so you would have to map the VLANs used on the dot1q trunks numbering higher than 1001 to VLANs on the ISL trunks. The simple answer is yes.
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  • mikearamamikearama Member Posts: 749
    Great... thanks.

    A follow up...

    Hucaby suggests that it's not mandatory for the native vlans to match on either end of a trunk. Clearly it's best practice... but if it's not mandatory, does it at least cause mega errors?

    Anyone seen a trunk with mismatched native vlans?

    Thanks.
    There are only 10 kinds of people... those who understand binary, and those that don't.

    CCIE Studies: Written passed: Jan 21/12 Lab Prep: Hours reading: 385. Hours labbing: 110

    Taking a time-out to add the CCVP. Capitalizing on a current IPT pilot project.
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  • dtlokeedtlokee Member Posts: 2,378 ■■■■□□□□□□
    In theory the native VLANs don't need to match but CDP will tell you about it and possibly destroy the trunk if it's set to dynamic. For this to work I would turn off CDP and set the interface to "switchport mode trunk". It isn't the best practice and I would try to avoid it.
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  • mikearamamikearama Member Posts: 749
    Never mind... it was in the ISL section. No need for matching native vlans there... native vlans period.

    My bad.

    EDIT... thanks for the quick reply dt. Preciate it.
    There are only 10 kinds of people... those who understand binary, and those that don't.

    CCIE Studies: Written passed: Jan 21/12 Lab Prep: Hours reading: 385. Hours labbing: 110

    Taking a time-out to add the CCVP. Capitalizing on a current IPT pilot project.
    · Share on FacebookShare on Twitter
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