From: Li Li (cslili@gmail.com)
Date: Thu Nov 03 2005 - 15:37:57 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(http://www.cisco.com/warp/public/459/25.shtml), 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) -----|
R2,R5,R6 are all in AS200. R5 and R6 are both EBGP to AS100. If R2 to
R5 metric is 10, R2 to R6 metric is 20, R2 will pick which path to
networkA?
According to the books, R2 should choose path via R6, which is a
confederation external route. But if follow that Cisco document, path
via R5 is better, becasue it has a lower IGP cost.
So which one is true?
Thanks,
Li
This archive was generated by hypermail 2.1.4 : Thu Dec 01 2005 - 09:12:05 GMT-3