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I apologise in advance I don't specialize in computer networks, but my tutor gave me this urgent task to analyze some raw data obtained from RIPE.

So basically I find a tool recommended by RIPE on github:

https://github.com/RIPE-NCC/bgpdump

and I think I run the program properly, I analyzed approximately tens of millions of pieces of data like this

TIME: 04/11/24 00:54:41
TYPE: BGP4MP/MESSAGE/Update
FROM: 2001:504:1::a506:2567:2 AS14061
TO: 2001:504:1::a501:2654:1 AS12654
ORIGIN: IGP
ASPATH: 14061 3356 1299 20473
MP_REACH_NLRI(IPv6 Unicast)
NEXT_HOP: 2001:504:1::a506:2567:2
NEXT_HOP: fe80::3e61:4ff:fe09:c13c
COMMUNITY: 3356:3 3356:22 3356:86 3356:575 3356:601 3356:666 3356:901 3356:2039 14061:400 14061:2000 14061:2001 14061:4000 14061:4004
ANNOUNCE
  2a0e:97c4:ae3f::/48

somehow I believe the data itself doesn't have any problem since I got them generated smoothly.

But I don't really understand this row:

ASPATH: 14061 3356 1299 20473

since

FROM: 2001:504:1::a506:2567:2 AS14061
TO: 2001:504:1::a501:2654:1 AS12654

Why this ASPATH end with a 20473 instead of 12654,

and there are also some data have a "right" ASPATH end with 12654?

In short, I know what ASN stand for, but I don't understand how it works in a routing network and how ASN participate in network transmission.

My English is not very good, thanks for all the answers.

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1 Answer 1

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The AS path is the AS number through which the BGP advertisement needs to pass in order to reach the destination AS.

Your advertisement passes through the ASes 14061, 3356, 1299, 20473 before reaching the destination AS 12654. The destination AS would not see its own AS number in the AS path.

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  • I checked the neighbours of AS20473 on this website: stat.ripe.net/app/launchpad turns out AS12654 isn't one of its neighbours. Could you please explain it in more detail ？
    – Lackind
    Commented Apr 13 at 8:26
  • It is very simple: each AS will prepend its AS number to the AS_PATH when advertising the prefix. That is really all there is to AS_PATH. Do not try to make more of it than there is. The last AS through which the advertisement passed is 14061. If 20473 and 12654 were neighbors, then the rest of the AS numbers would not be in the path.
    – Ron Maupin ♦
    Commented Apr 13 at 10:39

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