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Thread Index Re:[isp-bgp] How to properly utilize backup link in multi-homed setup?
Colo Host wrote: > first. I'm going to have to contact Foundry TAC on the route choice > thing. We're using Foundry routers and their algorithm is to prefer > IGP over EGP, opposite of Cisco's "administrative distance" factor > which treats IGP as a much lower preference to EGP. So in my case, > once the router determines that both hops are usable, local > preference is the same and AS path length is the same, it should > then choose IGP according to their docs but seems to be going with > EGP instead Hello Colo Host To my knowledge, Foundry also uses the Administrative weight parameter which overrides LOCAL_PREF, AS_PATH and ORIGIN. One must not confuse BGP administrative weight with Administrative distance. Weight is used to rank multiple routes to the same destination within BGP, Administrative distance is used to rank multiple contending paths to the same destination across different routing protocols. For ex: by default cisco uses a Administrative cost of 20 for EBGP, but 200 for IBGP while various IGPs have an Administrative distance in between ex: RIP 120, OSPF 110. Lower is better. So EBGP routes will be preferred over IGP and IGP over IBGP in Cisco. The reason IBGP has a very low preference is due to the potential of routing loops - AS_SEQUENCE is NOT exchanged between IBGP peers and the potential for routing loops exist if they enter the routing table hence IGP has preference. EBGP uses AS_SEQUENCE to detect routing loops so such a problem can be avoided. My guess is that any equivalent Administrative distance property of a route in Foundry should also follow the same ranking - based on the same principle, if not the exact values for distance..... Now I'm wondering if you are confusing Distance and Weight? ...If you are referring to preferences within the attribute ORIGIN - IGP/EGP/Unknown or the inter-protocol distance ranking .... This is because you mention IGP and EGP not IGP and EBGP Rgrds Rahul Sawarkar __________________________________ Do you Yahoo!? Yahoo! Mail - Easier than ever with enhanced search. Learn more. http://info.mail.yahoo.com/mail_250 To unsubscribe via postal mail, please contact us at: Jupitermedia Corp. Attn: Discussion List Management 475 Park Avenue South New York, NY 10016 Please include the email address which you have been contacted with. Copyright 2004 Jupitermedia Corporation All Rights Reserved. <- Previous Message | Next Message -> Thread Index |
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