Saturday, June 4, 2011

Can you run two AS Numbers in Single Router ? - Local AS

according to my experience we can't but similar functionalities given by Local AS option . It enables to act one AS for some of the neighbors and another AS for other neighbors

R2 connects to R1 using remote as 100 , but the R1 using remote-as as 2 rather than 300
R2#
router bgp 300
 no synchronization
 bgp log-neighbor-changes
 network 200.200.200.0
 neighbor 192.168.100.1 remote-as 100
 neighbor 192.168.100.1 local-as 2
R1#router bgp 100
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.100.2 remote-as 2
 no auto-summary
but when the route injected it shows originated AS as 300
R1#show ip bgp 
BGP table version is 2, local router ID is 192.168.100.1
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
*> 200.200.200.0    192.168.100.2            0             0 2 300 i

with no-prepend we can remove the local as prepending .
R2#show ip bgp 
BGP table version is 3, local router ID is 192.168.100.2
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
*> 100.100.100.0/24 192.168.100.1            0             0 100 i
*> 200.200.200.0    0.0.0.0                  0         32768 i
 
R2#router bgp 300
 no synchronization
 bgp log-neighbor-changes
 network 200.200.200.0
 neighbor 192.168.100.1 remote-as 100
 neighbor 192.168.100.1 local-as 2 no-prepend
 no auto-summary

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