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No Questions Asked!

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Forum Replies

  1. Hi Rene,
    Very Good Stuff.A quick questions for you …
    How R2 know R1 only 2 byte supported before sending any open message ??


  2. Hi Zaman,

    It doesn’t. When R2 receives a reply from R1 without the “support for 4-octet AS number capability” in its OPEN message, it knows that R1 doesn’t support it.

    You can see it in the wireshark capture:


    Take a look at the 1st packet from R2 and the 2nd packet from R1. R1 is missing the capability.

    Hope this helps!


  3. Hi Rene,
    I have question in 2-Byte & 4-Byte AS compatibility situation.

    In case of we adding R3 (AS3) and connect it to R2. R1 advertises one prefix (for example: to R2 and R2 will forward to R3.
    What will be in the AS path on R3? (22222222 1 or 23456 1)?


  4. Hello Minh

    This is an excellent question. Essentially what you are asking (allow me to put it more generally) is how is the AS path displayed when there is a 2-byte AS compatible router in the mix?

    Well, if you display the AS path on the 2-byte AS compatible router, then you will see the 23456 AS in place of the incompatible 4-byte AS number. So essentially the AS_TRANS attribute replaces the 4-byte AS number. However, the AS4 PATH number is an attribute that is received by the 2-byte AS compatible device, and is transitive. It may not understand it, but it

    ... Continue reading in our forum

  5. Thanks Laz for the explanation.

    Enjoy your weekend,

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