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100-101 CCENT Exam Topic Question

mgmguy1mgmguy1 Member Posts: 485 ■■■■□□□□□□
in CCNA & CCENT
I am looking over the new 100-101 exam topic PDF for what will be on the CCENT test.
I was looking at it and I did not see ISL mentioned in the PDF. I realize that 802.1q is the newer standard and ISL is not supported on newer switches. But am i correct in assuming ISL is not going to be a test subject ?


In addition please please let me know if I am missing any facts here.
IEEE 802.1q was created by IEEE.
Both ISL and 802.1Q tag each frame with a VLAN ID
The VLAN ID filed inside the 802.1Q Header, the 12-bit field supports a theoretical maximum of 4096 VLANS
802.1Q also defines one special VLAN ID on each Trunk as the Native VLAN.
"A lot of fellows nowadays have a B.A., M.D., or Ph.D. Unfortunately, they don't have a J.O.B."

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    arrogantbastardarrogantbastard Member Posts: 61 ■■□□□□□□□□
    Just rewatched the chris bryant video on this. dot1q has a 4 bit header, whereas ISL encapsulates with a header and trailer. An advantage to dot1q is if a native vlan is defined it further strips the header and sends out the frame untagged assuming the next switch will know it is to be switched in their native vlan. Can't tell you if ISL will be mentioned or not, the updated cisco academy still mentions ISL in their course material.
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    networker050184networker050184 Mod Posts: 11,962 Mod
    arrogantbastard wrote: »
    dot1q has a 4 bit header, whereas ISL encapsulates with a header and trailer.

    That's a 4 byte field inserted into the ethernet header, not a separate header which would be an encapsulation like ISL does.

    Looking at the exam topics for the 100-101 I don't see 802.1q or ISL specifically mentioned, but it only takes a few minutes to get yourself familiarized with the differences so it wouldn't hurt to have the knowledge just in case.
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    Magic JohnsonMagic Johnson Member Posts: 414
    802.1q is mentioned in Odom's book at least, ISL is but only referred to as being replaced by 802.1q, that's it. There is a blurb on 802.1q but nothing more really, you only need to know that it inserts a 4 byte tag as has been said, and even within that the only bit that is referenced is the 12 bit VLAN ID part.

    Further to this, it goes on to specify how to configure the trunk port (switchport trunk encapsulation {dot1q/isl/negotiate}).
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    mgmguy1mgmguy1 Member Posts: 485 ■■■■□□□□□□
    Just trying to make sure I cover all the bases. Wendell Odom's books are known to be very detailed and the PDF I have on the new exam objectives did not list ISL. I have noticed sometimes in taking tests that it's the small details that will kill you on a test and in real life!
    "A lot of fellows nowadays have a B.A., M.D., or Ph.D. Unfortunately, they don't have a J.O.B."

    Fats Domino
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    Magic JohnsonMagic Johnson Member Posts: 414
    mgmguy1 wrote: »
    Just trying to make sure I cover all the bases. Wendell Odom's books are known to be very detailed and the PDF I have on the new exam objectives did not list ISL. I have noticed sometimes in taking tests that it's the small details that will kill you on a test and in real life!

    The reason Odom gives for not delving further in is that most Cisco switches now do not support it. I'd imagine for completeness he showed the configuration options.

    EDIT: I'd be livid if there was a question about it in the exam! Haha.
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