Junos OS

Hello Community

Can some one please tell where do the originating AS exsists in the AS-Path sequence i.e at right most side or at left most side.

For example : AS 65000 AS 65002 AS 65003 (172.16/12)

If my local as is 65000 i will recieve the 172.16/12 subnet from 65003 with AS-Path as follows

172.16/12 AS-Path 65000 65002 65003(Originating As appears at right most side)

                                                     OR

172.16/12 AS-Path 65003 65002 65000(Originating As appears at left most side)

& what if just want to accept only the routes that originate in my adjacent AS wil Regex ".*adjacent As" suffice.

Thanks & Regards

Malik

Hi,

The originating AS is at the right most side.

If you want to receive prefixes originated only by neighboring AS, than it is as simple as this: "."

Hello Dumitru

Thnak you

Does this Regex for matching neighboring As is wrong

".*Neighbor As Number"

I mean what is wrong with the Regex above.

Regards

Malik

Hello,

---

If you want to receive prefixes originated only by neighboring AS, than it is as simple as this: "."

---

This regex does not allow prepending.

Rgds

Alex
 

Hi Alex

So what will be the correct regex if i just want to accept routes that originate in my adjacent as

Isn't this regex ".*As #" alright.

Regards

Malik

Hello,

If you want to accept routes originated by your adjacent AS, and you don't care how many ASNs are prepended, use this regex:

set policy-options adjacent-as-only "<adjacent AS#>$"

 If you want to accept routes originated by your adjacent AS, and you don't want to accept routes with more than 10 prepends, use this regex:

set policy-options adjacent-as-only-10prepends "<adjacent-AS#>{1,10}$"

Please PLEASE substitite <adjacent-AS#> with real ASN before using above regex.

HTH

Rgds

Alex

 Hi Alex

I think u r getting it wrong as i want to accept the routes that are originated in my adjacent AS.

As the originating AS appears last in the path i.e. at the right most side when i recieve it, so the regex .*65000 say if my adjacent AS is 65000  will be able to match all the routes just originated in 65000 .

It is like stack.

What do you think?

Regards

Malik

Hi Mailik,

In this case you should have as-path regex (assuming your peer AS no as 65000) as below:

policy-options {
    policy-statement import_peer {
        from {
            protocol bgp;
            neighbor 172.10.2.1;
            as-path peer_as;
        }
        then accept;
    }
    as-path peer_as ".* 65000";
}

Regards

Surya Prakash

Hello Surya

Thanks & hence this also employs that originating AS appears at the right most side in path.

Regards

Malik