BGP stands
for Border Gateway Protocol is true built-in policy based routing
protocols. BGP uses different attribute to implement these polices in
route selection process between different autonomous systems. There are
some main attributes that BGP uses in route selection process.
We will
configure here only weight attribute in detail and the remaining
attributes will be discussed in the next tips.
The
weight attribute basically a Cisco proprietary technology and considered
as first attribute in BGP. The default value of weight is 0 and the
range is from 0 to 65535.
If we change the weight
value of one router that change will not propagate to other router and
the route with maximum weight value will be considered as the best
route.
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 BGP. At the end, we will change the weight 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) #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) #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) #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 weight value.
C #show ip bgp
Then verify the routes in router C routing table, run the command
C #show ip route
Now change
the weight value on router C
in order to give it preference over a lower one.
In global
configuration Mode:
C(config)# router bgp 20
C (config-router) # neighbor 50.1.1.1 weight 100
Now again run show command to display the BGP updates on router C
with weight value 100.
C
#show ip bgp
COMPUTER TIPS