Hello,
I have 3 routers:-
150.150.150.0/24
----------------------------------------------------------------
|
|
|
|
R1 ---------------------------- R2----------------------------R3
(AS1) (AS2)
(AS3)
R1 - R2, R2 - R3 are using EBGP
I injected the network 150.150.150.0/24 into BGP from both R1 & R3. I have
enabled bgp always-compare-med to allow R2 to compare the MED from AS 1 & AS
3. I have also set a route-map on R3 so that when it advertise
150.150.150.0/24 to R2, it would have a metric of 20, as compared to 0 from
R1.
The thing I'm confused is that after I have enabled the command "bgp
bestpath med missing-as-worst", according to CCO, the MED of 0 from R1 would
now be considered as infinity (as confirmed by the debug messages), but why
is R2 still prefers the route from R1 instead of from R3?
Best Regards,
Hunt
RouterB#sh ip bgp 150.150.150.0/24
BGP routing table entry for 150.150.150.0/24, version 3
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
10.1.1.2
1
172.17.1.2 from 172.17.1.2 (20.20.20.1)
Origin IGP, metric 0, localpref 100, valid, external, best
3
10.1.1.2 from 10.1.1.2 (15.15.15.1) 10.1.1.2 to
main IP table
02:58:54: BGP: 172.17.1.2 rcv message type 4, length (excl. header) 0
02:58:54: BGP(0): 172.17.1.2 computing updates, afi 0, neighbor version 0,
table version 2, starting at 0.0.0.0
02:58:54: BGP(0): 172.17.1.2 send UPDATE (format) 150.150.150.0/24, next
172.17.1.1, metric 0, path 3
02:58:54: BGP(0): 172.17.1.2 1 updates enqueued (average=47, maximum=47)
02:58:54: BGP(0): 172.17.1.2 update run completed, afi 0, ran for 12ms,
neighbor version 0, start version 2, throttled to 2
02:58:54: BGP: 10.1.1.2 rcv message type 4, length (excl. header) 0
02:58:54: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin
i, metric 0, path 1
02:58:54: BGP(0): 172.17.1.2 rcvd 150.150.150.0/24
02:58:54: BGP(0): Revise route installing 150.150.150.0/24 -> 172.17.1.2 to
main IP table
02:59:17: BGP: Performing BGP general scanning
02:59:17: BGP(0): scanning IPv4 Unicast routing tables
02:59:17: BGP(IPv4 Unicast): Performing BGP Nexthop scanning for general
scan
02:59:17: BGP(1): scanning VPNv4 Unicast routing tables
02:59:17: BGP(VPNv4 Unicast): Performing BGP Nexthop scanning for general
scan
02:59:17: BGP(2): scanning IPv4 Multicast routing tables
02:59:18: BGP(IPv4 Multicast): Performing BGP Nexthop scanning for general
scan
02:59:22: BGP(0): 10.1.1.2 computing updates, afi 0, neighbor version 1,
table version 3, starting at 0.0.0.0
02:59:22: BGP(0): 10.1.1.2 send UPDATE (format) 150.150.150.0/24, next
10.1.1.1, metric 0, path 1
02:59:22: BGP(0): 10.1.1.2 1 updates enqueued (average=47, maximum=47)
02:59:22: BGP(0): 10.1.1.2 update run completed, afi 0, ran for 12ms,
neighbor version 1, start version 3, throttled to 3
02:59:23: BGP(0): 172.17.1.2 computing updates, afi 0, neighbor version 2,
table version 3, starting at 0.0.0.0
02:59:23: BGP(0): 172.17.1.2 send unreachable 150.150.150.0/24
02:59:23: BGP(0): 172.17.1.2 send UPDATE 150.150.150.0/24 -- unreachable
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=46255&t=46255
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