very simple topology i create 4 routers as a i put scenario's photo below
No special configuration very basic eBGP peering with physical interface
but output is weird
220.127.116.11 is also on R1
i've checked several times No special BGP config i did , but each time i face different outputs from command " show ip bgp "
R1 config :
router bgp 100
network 18.104.22.168 mask 255.255.255.255
network 22.214.171.124 mask 255.255.255.255
network 126.96.36.199 mask 255.255.255.255
network 188.8.131.52 mask 255.255.255.255
neighbor 192.168.12.2 remote-as 200
neighbor 192.168.13.3 remote-as 300
and similarly on R2 ...& others
but in R2 when i take output from show ip bgp
From R3 Output of show ip bgp
From R4 output as below
!!!!why R3 shows just 1 Best valid path while R2 shows both paths
i use "debug ip bgp neighbor 192.168.13.3 update" and i received below
logically yes it gets from originator and other paths it cant install
but why it should show like that !!!!
The AS numbers on the AS_PATH list are used for loop detection; a router receiving a BGP route with its own AS number in the AS_PATH assumes a loop and discards the route.
Its loop avoidance initiating it isn't a problem- Both R2 -R3 will advertise that prefix originating from R1 to R4 and R4 sees both paths from those rtts to that prefix as equal so it will possibly choose based on the oldest route or lowest bgp rid.
R4 will choose R2 as its best path so it will advertise the prefix it receives from R2 towards R3, As such R3 will also have two paths to that prefix and rtr2 will only have the one unless it loses connection towards R1 then it will obtain the prefix via rtr 4 -rtr3 path.