IBGP stands for
Internal Border Gateway Protocol use local preference attribute
to propagate the IBGP traffic to other autonomous systems. We use local
preference attribute in IBGP, if there are multiple exit path are
available from local autonomous system to destination.
The default
value of local preference is 100 and the range is from 0 to 4294967295.
If we change the local preference value of one router that change will
propagate to all other routers in same autonomous system and the route
with maximum local preference value will be considered as the best
route.
We will configure here
only local preference attribute in detail and the remaining attributes
will be discussed in the next tips. Today tip will help you configure
BGP between two different autonomous systems. In this case, we will try
to configure four different routers with routing protocols RIP and then
complete the all routing tables using EBGP and IBGP. At the end, we will
change the local preference of one route in order to give it preference
over a lower one.
Follow
the network topology of four different class networks in the given
figure:
Configuration BGP on Router A
In global configuration Mode:
A(config)# router bgp 10
A (config-router) # neighbor 40.1.1.2 remote-as 20
A (config-router) # neighbor 70.1.1.1 remote-as 20
A (config-router) # network 210.100.30.0
A (config-router) #end
Configuration to Enable BGP & RIP on Router B
In global configuration Mode:
B(config)# router bgp 20
B (config-router) # neighbor 40.1.1.1 remote-as 10
B (config-router) # neighbor 50.1.1.2 remote-as 20
B (config-router) # neighbor 60.1.1.2 remote-as 20
B (config-router) #no synchronization
B (config-router) #end
B (config) #router rip
B (config-router) # network 40.0.0.0
B (config-router) # network 50.0.0.0
B (config-router) #end
Configuration to Enable BGP & RIP on Router C
In global configuration Mode:
C(config)# router bgp 20
C (config-router) # neighbor 50.1.1.1 remote-as 20
C (config-router) # neighbor 60.1.1.2 remote-as 20
C (config-router) #no synchronization
C (config-router) #end
C (config) #router rip
C (config-router) # network 50.0.0.0
C (config-router) # network 60.0.0.0
C (config-router) #end
Configuration to Enable BGP & RIP on Router D
In global configuration Mode:
D(config)# router bgp 20
D (config-router) # neighbor 70.1.1.2 remote-as 10
D (config-router) # neighbor 50.1.1.1 remote-as 20
D (config-router) # neighbor 60.1.1.1 remote-as 20
D (config-router) #no synchronization
D (config-router) #end
D (config) #router rip
D (config-router) # network 70.0.0.0
D (config-router) # network 60.0.0.0
D (config-router) #end
Now run show command to display the BGP updates on router C with
default local
preference value.
C #show ip bgp
D #show ip bgp
Now change the
local preference value on router B (exit
point
router) in order to give it preference over a lower one.
In global configuration Mode:
B(config)# router bgp 20
B
(config-router) # bgp default local-preference 400
Now again run show command to display the BGP updates on C and D
router to verify the best exit path after changing the local preference
400.
C #show ip
bgp
D #show ip
bgp
COMPUTER TIPS