On Tue, Dec 14, 2010 at 6:03 PM, Michuki Mwangi <michuki@swiftkenya.com> wrote:
Hi Jamal,
On 12/14/10 12:42 PM, ibtisam jamal wrote:
Hi ,
I have this scenario i have 2 ISP's . I do eBGP with both of them. ISP 1 -send /24 subnets ISP 2 - send /23 subnets
Ok.
Could you confirm if you are the one originating the prefix (with your own ASN) or its your upstream provider? We are originating the prefix with own ASN
what we want to achieve is automatic failover .Such that if ISP1 fails traffic goes to ISP 2 automaticaly.
Ok.
But when testing this live ...something strange happens traffic goes out through ISP 1 which is wat we want .BUt incoming traffic uses ISP 2.
How it works is simple Routing information flows in opposite direction of traffic flow. That means if you were receiving traffic flow through ISP2 - it means your BGP announcements via ISP1 were not being advertised to the rest of the Internet as they should be.
Please log on onto any looking glass outside your network and review what the routing table looks like with your prefixes. An example of a looking glass is route-views.oregon-ix.net (use telnet).
For cisco there are good examples on the net but for juniper Mx series or just any junos we cant find examples.
The concept is the same only the command line is different but should achieve the same.
something about AS-PREPEND and playing with metrics.We want to keep it as simple as possible.THat why we opted to use the more specific subnet method.
Well AS-Path Prepend cannot do anything better than longer prefix match will do. Already if you are announcing longer prefixes (/24) via ISP1 then that should be your preferred inbound path to your network.
The only time in such a configuration that your traffic will come via ISP2 is when the announcements via ISP1 are withdrawn from the routing table.
To influence your outbound traffic use local preference where the default route received from ISP1 will have a higher local preference that the one from ISP2.
Thats basically as simple as it can get. There are instances to use AS-Path Prepend but its not the place to start.
Regards,
Michuki. |* * END * *|
Thanks Will do a test tonight and check the looking glass routes.