From: Leigh Harrison (ccileigh@gmail.com)
Date: Sat Oct 29 2005 - 09:46:40 GMT-3
Danny,
Use local-as prepend when you are lying to a neighbour about you AS
number, but don't want to pass that number to anyone.
i.e:
R1 -- bgp1-2 -- r2 -- ibgp3-3 -- r3
R1 peers with r2 using AS1 to AS2
R2 is actually running in AS3 and peers with r3 using ibgp
If you just put the normal neighbour statement on r2 to r1, then they
will not form a relationship, as they disagree on AS numbers. If you
put in the "neighbor 1.2.3.4 local-as 2" command, then they will form
the adjacency.
When any routes from R1 appear in the table of R3, they will have an AS
path of " 1 2 i "
Putting the command "neighbor 1.2.3.4 local-as 2 no-prepend" in will
ensure that r3 will only have an AS path of " 1 i "
LH
Danny Cox wrote:
>I've had an interesting time reading about local-as. The solutions to
>a lab I'm doing indicate that 'local-as 60 no-prepend' should be
>configured on one of the routers, R6. R6 is in AS 600.
>
>My reading of what 'local-as no-prepend' does, is that it will make
>sure that 60 (not 600) is not prepended to routes learned *by* R6 from
>its ebgp peers. It doesn't stop 600 being prepended to routes learned
>from R6 by its peers.
>
>Anyone agree with me here?
>
>Many thanks!
>
>Danny
>
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