Can someone explain why .2 /31 can ping and .4/31 cannot ping

[hfakoor222]

I have 2 routers

RouterA
interface FastEthernet1/0
description Link to AS30
ip address 100.122.1.2 255.255.255.254    (Can ping Router B)

duplex auto
speed auto







Router B

interface FastEthernet0/0
description Link to Central
ip address 100.122.1.3 255.255.255.254




RouterA
interface FastEthernet1/0
description Link to AS30
ip address 100.122.1.4 255.255.255.254    (Cannot ping Router B)

duplex auto
speed auto

Someone explain this to me please?

[MHM Cisco World]

this subnet give you 0 host, you can use one side .2/31 other .3/31
or better use /30 

https://packetlife.net/blog/2008/jun/18/using-31-bit-subnets-on-point-point-links/

[hfakoor222]

Broadcast address:  100.122.1.3  

clarified a lot for me.

Thanks

[MHM Cisco World]

Even if it broadcast it can use for p2p link,

Are you check link i attach?

[Paulo Thame · Accepted solution]

As you use a /31, it has 0 usable hosts per subnets.

Change the network for /30 , then you will be able to ping then.