BGP Regular expression ,

[Marc du]

Hi Guys

Refer to the attachment

which statement is true about this As filter accomplishes?
a. It filters BGP update with any AS number starting with the digit 5 and encoding ending with the digit 5, and this only in an AS_PATH
b. It filters incoming BGP update with any AS number matching “5.5”, but not 515,525.535 etc this only in an AS_SET
c. It filters incoming BGP update with any AS number starting with the digit 5 and ending with the digit 5 and this only in an AS_SET
d. If allows any number with the statement “.*” and this only in an AS_PATH.

i am confused between B and D ,kindly help

thanks

[mlund]

Hi

. means any single character

* zero or more of the character preceding the *

\ match the next character as a character not as a function

wich leads to .* means anything, and \. means match as a dot

so your list means "anything5.5anything"example 515.525 will match, 515.425 will not, nor 514.525

also 123.234.345.567 will match

/Mikael

[Marc du]

Hi michel

so B or D

thanks

[mlund · Accepted solution]

The list is read sequence, so first it will read line 1 and see if there is a match. If a match is found it will be denyed, and line 2 will not be involved.

If no match is found in line 1 it it will go to line 2, and line 2 is permitting anything.

So for A and C it will not match line 1, so it will be permitted by line 2

For B it will be a match for 515.525.535 because the pattern inside is 5.5 (actually it is matched twice), so it will be denyed.

For D, if the pattern will pass line 1 ( not matching 5.5) it will be permitted

/Mikael