BGP Extended Access-List Filtering

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.

Rene