AS-Path Regexp matching

RouterOS
1

I’m trying to use this format (from the documentation) but my devices (7.19.6) won’t accept it:

[ ]

[^ ]

Represents the set of AS numbers where one AS number from the list must match.

Use ^ after opening the bracket to negate the set.

It is also possible to reference the pre-defined num-lists from num-list with [[:numset_name:]]

^[1234 5678 1-100]

will match the AS-path that starts with 1234 or 5678 or from the range of 1 to 100

Ideally I’m looking to match any one of a group of AS numbers at the start of the BGP path.

Thanks,

Luke

2

What’s the filter command you are trying to add, and what happens when you try it?

Something like this should work:

if (bgp-as-path [[:match_these:]]^) {action}

And a num-list:

/routing filter num-list add disabled=no list=match_these range=65534

3

Don’t use regexp matching of the AS path for that, it is inefficient and cannot match the start of the path.

Use bgp-input-remote-as to select the AS number of the peer. You can use a number set to match multiple numbers (but not as a regexp, you can use a range).

4

Unfortunately this isn’t what I need to do - we’re looking to set route attributes for certain remote AS numbers (the peer in this case is a route server not an individual AS)

5

As an example of the exact syntax I’m trying to use (taken from the documentation)

if (bgp-as-path ^[1234 5678 1-100]) { set suppress-hw-offload no }

"Word {bgp-as-path} Word {^[1234} Word {5678} Word {1-100]} " - invalid bgp-as-path regexp (6)

6

It seems to want the regexp in quotes. Your option works too and might be better for what I need - thanks

7

It is unclear to me why you write ^[1234 5678 1-100] when you want it to “match anywhere in the path”.

The ^[ means “at the beginning of the path”. It means “negation” only when inside the brackets like [^

8

It is unclear to me why you write ^[1234 5678 1-100] when you want it to “match anywhere in the path”.

I was always trying to match the first AS in the path only, hence why I used “^”