From: Angelo De Guzman (a.deguzman@wesolv.ph.fujitsu.com)
Date: Thu Aug 31 2006 - 22:10:00 ART
Thanks!
So without changing the as path that comes from R9. Maybe I should change my
advertisement out of R9. This way even if R6 prefers these routes through AS1
it will still advertise these routes to R4 because I did not change any local
attribute within AS 567. Am I correct?
( I am not able to try this but I guess this will be correct)
Gianpietro Lavado (9/1/06 12:41 AM):
>
>The explanation is: when a router has two BGP possible routes, and picks one
>of them, it only advertises the preferred one to its neighbors; so in this
>case, when you activate the prepend, only R6 is holding the two possible
>routes, and since it prefers the one that comes from AS 1, it will not
>advertise the other one (from AS 9) to AS 24 or to R5.
>When R6 looses the route coming from AS 1 (turning off the R1 peering), its
>new preferred route is through AS 9, so it starts advertising this route to
>AS 24 and R5.
>
>HTH
>
>Gianpietro
>
>
>On 8/31/06, Ivan <ivan@iip.net> wrote:
>>
>> AS1 and AS9 announce 10.34.19.32/28 and 10.34.19.0/28 after peering with
>> R1
>> shut off AS24 see path to this prefixes through AS567 and 2-a prepends.
>>
>> *> 10.34.19.0/28 192.168.6.6 0 567 9 9 9 i
>> *> 10.34.19.32/28 192.168.6.6 0 567 9 9 9 i
>>
>>
>> > Hi,
>> > R1 AS 1 peers with R2 AS 24
>> > R2 peers with R4 AS 24
>> > R5 AS 256 and R6 AS 256
>> >
>> > R5 peers with R2 in AS 24, and R6 peers with R4 in as 24
>> >
>> > R6 peers to R9 in AS 9
>> >
>> > Both R9 and R1 are advertising the same route.
>> >
>> > When I do as path prepend for the routes coming into R6 (from R9)
>> these
>> > routes dissappears from AS 24.
>> >
>> > Is this normal? If I removed the peering to R1 then the bgp routes
>> comes
>> > back. Any explanation why R4 is not installaing the BGP routes at the
>> same
>> > time at R4? I guess it has something to do with the AS Path but I need
>> more
>> > clarification on this matter.
>> >
>> > ******NO AS Path prepend at R6 yet*******
>> > R4#sh ip bgp
>> > BGP table version is 5, local router ID is 192.168.4.4
>> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
>> > internal, r RIB-failure, S Stale
>> > Origin codes: i - IGP, e - EGP, ? - incomplete
>> >
>> > Network Next Hop Metric LocPrf Weight Path
>> > * 10.34.19.0/28 192.168.6.6 0 567 9 i
>> > *>i 192.168.1.1 0 100 0 1 i
>> > *> 10.34.19.0/26 192.168.6.6 0 567 9 i
>> > * i 192.168.5.5 0 100 0 567 9 i
>> > * 10.34.19.32/28 192.168.6.6 0 567 9 i
>> > *>i 192.168.1.1 0 100 0 1 i
>> > *> 172.16.80.0/27 192.168.6.6 0 567 7 8 ?
>> > * i 192.168.5.5 0 100 0 567 7 8 ?
>> > R4#
>> > *Aug 31 15:39:29.746: %BGP-5-ADJCHANGE: neighbor 192.168.6.6 Down Peer
>> > closed th e session
>> > *Aug 31 15:39:29.978: %BGP-5-ADJCHANGE: neighbor 192.168.6.6 Up
>> >
>> > **** With AS path prepend at R6*****
>> > !
>> > access-list 1 permit 10.34.19.0 0.0.0.15
>> > access-list 1 permit 10.34.19.16 0.0.0.15
>> > access-list 1 permit 10.34.19.32 0.0.0.15
>> > !
>> > route-map ADDAS permit 10
>> > match ip address 1
>> > set as-path prepend 9 9
>> > !
>> > ******************************************
>> > R4#sh ip bgp
>> > BGP table version is 8, local router ID is 192.168.4.4
>> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
>> > internal, r RIB-failure, S Stale
>> > Origin codes: i - IGP, e - EGP, ? - incomplete
>> >
>> > Network Next Hop Metric LocPrf Weight Path
>> > *>i10.34.19.0/28 192.168.1.1 0 100 0 1 i
>> > *>i10.34.19.32/28 192.168.1.1 0 100 0 1 i
>> > *>i172.16.80.0/27 192.168.5.5 0 100 0 567 7 8 ?
>> >
>> > ****Turning off the R1 peering******
>> > R4#sh ip bgp
>> > BGP table version is 14, local router ID is 192.168.4.4
>> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
>> > internal, r RIB-failure, S Stale
>> > Origin codes: i - IGP, e - EGP, ? - incomplete
>> >
>> > Network Next Hop Metric LocPrf Weight Path
>> > *> 10.34.19.0/28 192.168.6.6 0 567 9 9 9 i
>> > *> 10.34.19.0/26 192.168.6.6 0 567 9 9 9 i
>> > *> 10.34.19.32/28 192.168.6.6 0 567 9 9 9 i
>> > *> 172.16.80.0/27 192.168.6.6 0 567 7 8 ?
>> > * i 192.168.5.5 0 100 0 567 7 8 ?
>> >
>> > TIA,
>> > Angelo
>> >
>> >
>> >
>> > ***********************
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>>
>> --
>> Ivan
>>
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This archive was generated by hypermail 2.1.4 : Fri Sep 01 2006 - 15:41:59 ART