From: Li Li (cslili@gmail.com)
Date: Thu Nov 03 2005 - 14:18:01 GMT-3
*Routing TCP/IP volumn2* and *Internet Routing Architectures *both said that
EBGP routes is preferred over confederation external routes,which is better
than IBGP routes.
But in Cisco latest topic of BGP Best Path Selection Algorithm, No.7 is:
*Prefer eBGP over iBGP paths. If bestpath is selected, go to Step 9
(multipath). Note: Paths that contain AS_CONFED_SEQUENCE and AS_CONFED_SET
are local to the confederation. Therefore, these paths are treated as
internal paths. There is no distinction between Confederation External and
Confederation Internal.*
**
Consider following scenario:
R2 (confed 65002) --- R5 (confed 65002) ---networkA(as100)
| |
|-------------------------- R6 (confed 65001) -----|
If R2 to R5 cost is 10, R2 to R6 cost is 20, R2 will pick which path to
networkA?
According to the books, R2 should choose path via R6, which is the
confederation external route. But if follow that Cisco document, path via R5
is better, becasue it has the lower IGP cost.
So which one is true?
Thanks,
Li
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