AS Number

Unanswered Question
Nov 29th, 2007

Hai frenz, may be an easy question to you all but i have doubt ...pls do help me

1.why do we need AS Number, what situation AS number is needed??

3.if my customer using AS do i also need to have AS to talk to his router

4.if i dont have AS .. can i route traffic that have AS number.

pls need help...???? TQ

I have this problem too.
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Paolo Bevilacqua Thu, 11/29/2007 - 11:31

1 for bgp to the internet

2 ditto

3 no

4 traffic never has as number. you can caryy traffic for any network your ISP allows, and you have ask them if BGP is a requisite for that.

paul.matthews Fri, 11/30/2007 - 02:21

AS numbers dentify the network - they are most commonly used with BGP, but are also applicable to(E)IGRP.

An AS number is needed when using BGP or (E)IGRP

As for you needing one, it depends! there areother ways - a simple static route may be enough to get things working.

You will need an AS Number to participate in the routing protocols that use them, but AS for (E)IGRP are normally locally allcated, and for BGP there are ways to do it withut needing to go the whole hog.

chenoi2007 Fri, 11/30/2007 - 02:58

i have one scenario like this

current setup


New Plan


Midle ISP have core router but dont have ASN they only running static route. can this middle router route customer ASN to ASN_upstream without having ASN? middle ISP only act as a middle man. can this be done if my customer insist to have their ASN talk to provider ASN.

Please verified this. TQ

osiristrading123 Fri, 11/30/2007 - 04:23

EBGP multihop will allow you to run the configuration above. You will still need to have the IP range routed to the customer statically or with some other IGP (or MIDDLE_ISP won't know how to route the packets through to the customer).

In addition, the loopback or other addresses used to originate the BGP sessions will need to be reachable from either side.

chenoi2007 Fri, 11/30/2007 - 09:33

do you mean even do middle_isp dont have ASN it still able to talk to 2 different AS Cloud with nly eBGP? Please, I need some sample configuration and a network diagram to make my understand better. i hope you can provide me with the sample confg.

Danilo Dy Sun, 12/02/2007 - 06:16


Since MIDDLE_ISP have direct connection to cust_rtr(ASN) and (ASN)Ups_routr, try building IP/GRE Tunnel between cust_rtr(ASN) and (ASN)Ups_routr over MIDDLE_ISP and run BGP on it. Remain static route between cust_rtr(ASN) and MIDDLE_ISP, MIDDLE_ISP and (ASN)Ups_routr. Anyway, MIDDLE_ISP will always be a middle man between cust_rtr(ASN) and (ASN)Ups_routr :)




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