From: Carlos Chorao (cchorao@xxxxxxxxxx)
Date: Wed Nov 28 2001 - 01:48:57 GMT-3
This question relates to the case set out in Doyle vol page 219. The
typology is set out on page 212.
Apologies to those that don't have Doyle on hand.
The facts are as follows
1) As 30 is multihomed
2) The 2 edge devices in as 30 are not peered i.e. no iBgp in as 30
3) The 2 edge routers redis their BGP routes into IGP - ISIS in this case
4) The 2 edge routers redis IGP into BGP
The net result is that at least one of the edge devices in AS 30 will/could
feedback routes learned from other AS back into BGP showing AS 30 as the
originating router.
On page 220 in example 3-84 Doyle shows that this feedback can be avoided
by applying a filter list ensuring that AS30 only advertises routes
originating from the AS to other peers i.e." ip as-path access-list 1 permit
^$ "
My question is how will this avoid the feedback problem , all the path info
is lost when the BGP redistributes into ISIS , when the "external routes
are redis back into BGP at one of the edge devices in AS30 they show as
having originated internally and therefore slip past the filter list.
Tx
Carlos
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