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Notable Replies

  1. awesome lessons! didnt know you can use extended access-list like this!

    correct me if im wrong, the difference i see here is that, its working like a prefix-list but you can only use "greater than or equal to"?

    on your examples, it only shows like:

    -/24 to /32

    -/25 to /32

    -/26 to /32

    is it possible to have /24 to /30 only? /26 to /29? what will be your subnet and subnet wild card?



  2. Hi John,

    Good question, it can't be done...let's look at an example:

    00000000 /24
    10000000 /25
    11000000 /26
    11100000 /27
    11110000 /28
    11111000 /29
    11111100 /30
    11111110 /31
    11111111 /32

    Let's say you want to match /26 up to /29, the problem is that they don't have a lot of bits in common...only the first two bits are the same:

    11000000 /26
    11100000 /27
    11110000 /28
    11111000 /29

    Now if you would use wildcard 00111111 (63 in decimal) then it matches /26, /27, /28, /29 but also /30, /31 and /32.

    It can't be done in one statement but of course you can use multiple statements...just create one for /26, /27, /28 and /29 and you are done.


  3. Hi Rene/All,

    I got Problem for the attached toplogy ,R4 contains Two network 44 and 55 ,R2 at AS2 got to network 44 through R3 in AS1 ,and go to net 55 through R1 in AS1 using AS prepending in R1 and R3 the border AS Router in AS1 ,but the problem all traffic from R4 to network at r2 AS2 ,unsing source address 55 and 44 go out AS1 to AS2 through R1 the lowest Router id , my request when go to at r1 As1 with source address 44 go through r3 and to go to with sources address 55 go through R1 .,the toplogy attached.


  4. Hi Shady,

    If you want to enforce one path for outgoing traffic from AS 1 to AS 2 then it's best to influence the attributes. Don't let the router ID decide it. If you want to do this for the entire AS, it's best to configure local preference inbound on R1 and/or R3.


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