The 192.168.0.0 network is not being propagated throughout the network. Observe the BGP
configuration commands from the advertising router.What is the reason the 192.168.0.0
route is not being advertised?
router bgp 65111
neighbor 172.16.1.1 remote-as 65111
neighbor 172.16.2.1 remote-as 65112
network 192.168.0.0
network 10.0.0.0
!
ip route 192.168.0.0 255.255.0.0 null0
Select the best response.
A.
Thenetwork 192.168.0.0statement is missing mask 255.255.0.0
B.
The network 192.168.0.0statement is missing mask 0.0.255.255.
C.
The network 10.0.0.0statement is missing mask 255.0.0.0.
D.
The network 10.0.0.0statement is missing mask 0.255.255.255.
E.
The auto-summaryconfiguration is missing.
Explanation:
The “network” statement in other routing protocols (EIGRP, OSPF, RIP…) is used to enable
routing protocol on the interfaces within that “network” statement. But in BGP, the function
of a network statement is to tell the router to search the IP routing table for a particular
network, and if that network is found, originate itinto the BGP database. But notice that you
must have an exact match in the IP routing table toappear the network in the BGP routing
table (in this case we don’t see the auto-summary command so we suppose it is disabled in
this case). For example:
+ network 10.10.10.0/8 will appear in BGP if network 10.10.10/8 appears in the IP routing
table.
+ network 10.10.10.0/24 will appear in BGP if network 10.10.10.0/24 appears in the IP
routing table.
Therefore, in this question the static route “ip route 192.168.0.0 255.255.0.0 null0″was used
to put a route to 192.168.0.0/16 into the routing table (although it points to Null0 but this
command really makes that route appears in the routing table). But the “network
192.168.0.0″statement tells the router to lookup network 192.168.0.0/24 (if the network
statement under BGP-mode does not specify a subnet mask, the default subnet mask of
that class will be used). The router only finds network 192.168.0.0/16 -> The network
192.168.0.0 is not being propagated throughout the network because of the mismatch of the
subnet mask -> A is correct.
Just for your information, in fact we have to suppose there is no entry of the network
192.168.0.0/24 exist in the routing table except the static route “ip route 192.168.0.0
255.255.0.0 null0″. If such an entry exists (for example, a directly connected entry like “C
192.168.0.0/24 is directly connected”) then the router still advertises it with the “network
192.168.0.0″(without mask 255.255.0.0) command.