Examine the exhibit. You have determined that RTR2 is not advertising the CIDR summary address 192.168.0.0 to the other routers in AS 65100.

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RTR2(config)# router bgp 65100
RTR2(config-router)# neighbor 172.16.1.2 remote-as 65101
RTR2(config-router)# neighbor 192.168.3.2 remote-as 65100
RTR2(config-router)# network 192.168.0.0 mask 255.255.0.0
RTR2(config-router)# ip route 192.168.0.0 255.255.0.0 null 0

The network command specifies the address that will be inserted into the BGP table. Without the mask keyword, the classful network will be assumed. Because 255.255.0.0, or /16, is not the natural mask for any Class C address, the mask keyword must also be specified. Thus, 192.168.0.0 and 255.255.0.0 identify the desired address and mask of the 192.168.0.0/16 network prefix.

The router checks the IP forwarding table for an exact match before it advertises the route. Without a matching entry in the IP forwarding table, that route will not be advertised. RTR2 must be able to advertise a CIDR block and not the individual subnets. A static route is required because BGP requires that a match of the network prefix be present in the forwarding table when using the network command with the mask keyword. Therefore, to ensure an exact match for the identified prefix exists in the IP forwarding table, and to ensure that the prefix will always be advertised, a static route for 192.168.0.0/16 to null 0 is also required.

The syntax for the network command is shown below:

network network-number [ mask network-mask ] [ route-map map-tag ]

The parameters are:
mask – This parameter is optional and identifies the network or subnetwork to advertise.
route-map – This parameter is optional and identifies a preconfigured route-map that will be used to filter specific addresses from being advertised.

The following command set is missing the mask keyword in the network command and the command to create a static route to null 0. The address used in the network command is also incorrect. It should 192.168.0.0:

router bgp 65100
neighbor 172.16.1.2 remote-as 65100
neighbor 192.168.3.2 remote-as 65100
network 192.168.3.0

The following command set is missing the mask keyword in the network command and the command to create a static route to null 0:

router bgp 65100
neighbor 172.16.1.2 remote-as 65101
neighbor 192.168.3.2 remote-as 65100
network 192.168.0.0

The following command set uses an incorrect mask (255.0.0.0) in the command that creates the static route to null 0. It should be 255.255.0.0:

router bgp 65100
neighbor 172.16.1.2 remote-as 65100
neighbor 192.168.3.2 remote-as 65100
network 192.168.0.0 mask 255.255.0.0
ip route 192.0.0.0 255.0.0.0 null 0

Objective:
Layer 3 Technologies
Sub-Objective:
Describe, configure, and verify BGP peer relationships and authentication

• 300-410 : All Parts