BGP AS-Path Changing

[hopak]

Hello There,

I have a Cisco Catalyst 8500 Router. I run BGP on this router. I have a neighborship with my datacenter and i get the full route from they.

I Want to replace the as-path to some networks/as paths by regex/static.

How can i do that?

What i want;

In my route table when i want to go 1.0.128.0/24 i must use the 0 42xxx 6939 4651 23969

*> 1.0.128.0/24 77.92.xxx.xx 200 0 42xxx 6939 4651 23969

But i want to use this path for going to 1.0.128.0/24 0 42xxx 159xx

Can i do that?

When i tried the prepend it does 42xxx 159xx 42xxx 6939 4651 23969

This is my bgp configuration;

this is my bgp configuration;
router bgp xxxx
bgp log-neighbor-changes
neighbor 77.92.xxx.xx remote-as 42xxx
neighbor 77.92.xxx.xx log-neighbor-changes
neighbor 77.92.xxx.xx ebgp-multihop 255
neighbor 77.92.xxx.xx transport connection-mode active
neighbor 77.92.xxx.xx update-source TenGigabitEthernet0/1/0
!
address-family ipv4
network 77.92.xxx.xx mask 255.255.255.224
neighbor 77.92.xxx.xx activate
neighbor 77.92.xxx.xx soft-reconfiguration inbound
neighbor 77.92.xxx.xx route-map PDC_IN in
neighbor 77.92.xxx.xx route-map PDC_OUT out
exit-address-family

route-map PDC_IN permit 10

set local-preference 200

!

route-map PDC_OUT permit 10

match ip address prefix-list announces

[M02@rt37]

Hello @hopak 

You want replace all AS-PATH in inbound ?

[hopak]

When i do it i will check from show ip bgp x.x.x.x

it shows me those path 42xxx 159xx 42xxx 6939 4651 23969
I apply this policy to in may i use this to out policy?

I want to specify also inbound and outbound as-path for some ip/asns

[M02@rt37]

@hopak 

Modify full path is impossible. You could delete private ASN, replace-as with your ASN, prepend the AS-PATH in order to influence ingress flow.

[MHM Cisco World]

I think You can try

Use route-map 

And set as-path replace 

Note:- please note that even if this work you maybe see routing loop since you change attribute bgp use to detect loop.

Thanks

MHM

[Giuseppe Larosa]

Hello @hopak ,

you can use local preference in a route-map to prefer a path over another

By the way you likely have a local preference set to 200 on the current best path

*> 1.0.128.0/24 77.92.xxx.xx 200 0 42xxx 6939 4651 23969

But i want to use this path for going to 1.0.128.0/24 0 42xxx 159xx

The route-map has to be applied inbound on the neighbor that you want to increase the local preference using prefix-lists you can do this in a selective way.

Hope to help

Giuseppe