route-filter BGP AS-PATH manipulation

RouterOS Forwarding Protocols
1

Hello

I have a AS-PATH with an internet exchange in the middle. Actually one of my peers kind of acts like an exchange.
I want to remove the AS number of the peer in the middle which is inside the AS PATH (as normally the AS number of the internet exchange is not seen).

so I want to do a rule like this

if (bgp-as-path ^123,456$) { set bgp-as-path=456;}

but bgp-as-path is a read only property. So this doesn’t work.

How can the first AS number in a path be removed (only applies to certain paths, not all, so it can not be set as option on the connection)

2

Manipulating as path with filters is not allowed.
But you can set prepend to 0 to remove last ASN.

3

removing the last ASN is not what I want. I need to remove the FIRST ASN

4

It’s in the manual

In 7 bgp-as-path itself is immutable you can’t change it and you can’t directly remove individual AS numbers from the AS-PATH using filters.

You will need to find another way.

5

hmm… interesting)

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want to remove the AS number of the peer in the middle which is inside the AS PATH (as normally the AS number of the internet exchange is not seen).
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if you did peered with the ix - maybe you can propose to do a kind of confederation with them. hence you won’t see their actual asn anywhere along the path.

but.. this confederation won’t make any global routing changes if you do it with private asn. just be careful with it so you won’t disrupt the world.

6

every internet exchange with a route server basically does not insert their own AS. This is important to not increase the path lengths artificially.
Now I have one guy playing as a internet excange but he inserts his AS number which I want to remove again so routing is more smoothly. But it seems mikrotik cant do that sight

7

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Now I have one guy playing as a internet excange but he inserts his AS number which I want to remove again so routing is more smoothly. But it seems mikrotik cant do that sight
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no no)) this is not MT problem))

sometimes it’s normal to see some ix having their own asn attached. some ix do have their own legitimate address block for their data center. ie. rack rental vps facility etc. supplied by the layer 2 providers.

so… it’s depends on you yourself for the approach.