[j-nsp] as-path rewrite

[Rafal Szarecki (WA/EPO)]

Sorin,

The juniper "set loops 2" is the same as ciscos "allow-in". So What do not use them if you use allows-in?

Try to use AS-overide on ebgp session. this has to be don on AS2 CE on session to global instance.

"local-as" do not solve your problem. This do not overwrite real AS. thay just add "virtual" AS in between neighbors. If you define AS3 as local AS between AS 1 and AS 99, on path you will see "1 3 99 2".

Rewrittink of AS-PATH is impossible. And this is good. Let imagine World wide inconsistency. AS pre RFC1771 AS-PATH attribute is used to AVOID LOOPS. So any misteak here can ...

The other concept is to as customer to:
do not advertize prefixes lerned from VPN to Internet connection (wuith AS1 on path)
create aggregate route on CE in AS2 which represent whole AS1.

Sorin, are you work for ROMTELECOM?

Rafal Jan Szarecki JNCIE #136
Senior Consultant - Datacom Networks
Ericsson Poland EPO/S/D
Office: +48 22 6916635
ECN:    837 6635
Mobile: +48 602418971
Skype: callto://Rafal_Szarecki <callto://Rafal_Szarecki/> 




> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net 
> [mailto:juniper-nsp-bounces at puck.nether.net]On Behalf Of 
> Sorin CONSTANTINESCU
> Sent: Tuesday, September 27, 2005 12:17 PM
> To: juniper-nsp at puck.nether.net
> Subject: [j-nsp] as-path rewrite
> 
> 
> Hi, all.
> 
> I have the following topology:
> 
> AS1 - AS99 (L3 Mpls VPN) - AS2 - AS99 - INTERNET
> 
> My customer (AS2 - public AS Number) buys from the company i work for
> 2 services:
> 
> 1) Internet Access
> 2) VPN between his location, and AS1 (also public AS Number).
> 
> The problem i have is that when i receive a prefix originated by AS1
> on the Internet Transit BGP session, the AS-PATH is: 1 99 2 . Our
> network is a mixture of Juniper and Cisco routers. I used "allowas-in"
> on the neighbor to the customer, but the Juniper routers won't import
> this prefix throughout the network. I know i can use
> 
> a at R1# set loops ?
> Possible completions:
>   <loops>              Maximum number of times this AS can be in an AS
> path (1..10)
> [edit routing-options autonomous-system]
> a at R1# set loops
> 
> ... but i don't consider this an option.
> 
> Has anyone ever ran into this problem? As far as i see it, i have the
> following options:
> 
> - use private "local-as" for the BGP sessions between AS99 and AS1/AS2
> for the MPLS VPN BGP sessions (haven't tested this one so far)
> - ask the customer to configure EBGP Multihop between AS1 and AS2, so
> that my own AS won't be in the AS-PATH
> 
> I wish i could AS-PATH rewrite :))
> 
> Thanks,
> --
> Sorin CONSTANTINESCU
> Cisco CCNP / JNCIA #845
> consta at gmail.com
> 
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