Mask info doesnt show up in BGP config after it is entered

[Craddockc]

Community,

I am entering the network info under my BGP config and am noticing that the 192 subnets are  not showing the Mask info even after Ive entered it but my other subnets are. I do get the mask option when entering the "network" command, I key in the mask 255.255.255.0 but when I do a show run the mask is nowhere to be found. Why is that? Does this mean BGP is going to take the classful /24 by default now? The subnets are /24 anyway but Im still left wondering why the mask info is not there. Thanks.

router bgp xxxxx
 no synchronization
 no bgp log-neighbor-changes
 network 10.120.40.0 mask 255.255.255.0
 network 10.120.55.0 mask 255.255.255.0
 network 10.120.61.0 mask 255.255.255.0
 network 10.251.1.0 mask 255.255.255.252
 network 192.168.25.0
 network 192.168.30.0
 network 192.168.50.0
 neighbor 10.251.1.0 remote-as xxxxx
 neighbor 10.251.1.0 timers 15 45
 no auto-summary

!
ip classless

(config-router)#network 192.168.50.0 ?
  backdoor   Specify a BGP backdoor route
  mask       Network mask
  route-map  Route-map to modify the attributes
  <cr>

[Vinit Jain · Accepted solution]

This is an expected behavior if the subnet that you are entering is a classful subnet and the actual subnet of that address is also same. Then it will not show the mask command.

[Vinit Jain]

Below is another example.

R1(config)#int lo10

R1(config-if)#ip add 172.16.0.1 255.255.0.0
R1(config-if)#router bgp 100
R1(config-router)#add ipv4
R1(config-router-af)#net 172.16.0.0 mask 255.255.0.0
R1(config-router-af)#end
R1#sh run | s r b
router bgp 100
 bgp router-id 192.168.1.1
 bgp log-neighbor-changes
 neighbor 192.168.2.2 remote-as 100
 neighbor 192.168.2.2 update-source Loopback0
 !
 address-family ipv4
 network 172.16.0.0
neighbor 192.168.2.2 activate
 neighbor 192.168.2.2 next-hop-self
 exit-address-family

[Craddockc]

Thank you! This was very helpful.

[Craddockc]

Vinit,

WOW! That makes perfect sense! The 10.x.x.x networks are class A network by nature so the mask will show if its different where the 192 subnets are class C's by nature and since the mask is class C it wont show. Thanks!