BGP regular expression for 4-byte AS numbers
Hi;
I'm working on a topology and trying to test regular expression. I have used 4-bytes AS numbers and have written the regular expression as this:
ip as-path access 2 permit ^[1-9]+$
I want to permit the routes that are local to the neighboring ASs (I mean the routes with only one AS in AS_PATH). I applied it to the neighbors with filter-list command but it blocked all the routes from the neighbors. regarding to the fact that I have used 4-buyes AS numbers on routers, the BGP routes are shown like this on devices:
* 15.15.15.5/32 9.9.9.1 0 19661100 32768500 i
*> 11.11.11.1 0 19661100 32768500 i
* i 5.5.5.2 0 100 0 400 32768500 i
if the as numbers shown above were in decimal values, the regular expression should worked fine, but it didn't. I suppose that writing regular expression for 4-byte AS numbers must be different. how can I achieve my goal in this scenario?
anyway if there is a good article about using regular expression for 4-byte AS numbers, please let me know. tnx a lot.
Comments
There has to be something wrong in your configuration, or you did not do a route-refresh after applying the filter. Between 2-byte and 4-byte AS number there is a single difference, that the 4-byte AS number can be displayed with or without the '.' by using command "bgp asnotation dot". If you choose to display the '.' and want to match on that AS number you need to match on the '.' as well in your regex.
You should be able to test your regexp with show ip bgp regexp <expression>.
Hi Timaz and All,
ip as-path access 2 permit ^[1-9]+$
Don't the anchors: ^ and $
Limit the list to match but single ASN?
bgp table entries all appear to have 2 ASNs in AS Path
yes! I need to permit just the networks originated inside the neigboring ASs. this regular expression must work, but it doesn't. maybe I'm using 4-byte AS numbers and there should be a trick somewhere.
Hi Timaz and All,
Got it. I'm getting old and sometimes miss the point. Looks like a great Lab problem![:)]
Will study tonight.//RandyB
following the example in my previous topic, I faced with another example of this. I had some networks in my BGP table and want to aggregate them into one summary route: 8.0.0.0/5.
my subnets in my BGP table are as follows, for clarity, I deleted unrelevant parts of the output, so only networks and AS-PATH information are shown as follows:
9.9.9.5/32----19661100 i
10.10.10.5/32----32768 i
11.11.11.5/32----19661100 i
12.12.12.1/32----19661100 i
12.12.12.2/32----19661100 i
12.12.12.3/32----19661100 i
12.12.12.4/32----19661100 i
12.12.12.5/32----19661100 i
12.12.12.6/32----19661100 i
12.12.12.7/32----19661100 i
12.12.12.8/32----19661100 i
12.12.12.9/32----19661100 i
12.12.12.10/32---19661100 i
12.12.12.11/32---19661100 i
12.12.12.12/32---19661100 i
13.13.13.5/32----19661100 32768500 i
15.15.15.5/32----19661100 32768500 i
I wrote these commands on the aggregating router:
router bgp 200.200
aggregate-address 8.0.0.0 248.0.0.0 as-set advertise-map ADV_MAP
!
route-map ADV_MAP permit 10
match as-path 3
!
ip as-path access-list 3 permit _19661100_
ip as-path access-list 3 permit _32768500_
but again the router does not produce any aggregate route based on the advertised-map that has written. I think this problem relates to the regular expression about 4-bytes as numbers. because I have used 4-bytes AS numbers throughout my topology, I should find a solution to this issue. any ideas?
Hi Timaz and All,
Your commands look appropriate and correct. I used same commands with 15.3(1) IOL and had success.
using your commands:
1) R6#show ip as-path-access-list
AS path access list 7
permit ^[0-9]+$
AS path access list 67
permit 458759 589833
R6#
R6#show route-map
route-map BGP_R7_IN, permit, sequence 10
Match clauses:
as-path (as-path filter): 7 67
Set clauses:
Policy routing matches: 0 packets, 0 bytes
3) Got matches for:
R6#show ip bgp route-map BGP_R7_IN