To share what I've learned !

 this blog we will look the PPP link's ip route / address negotiation . In the above diagram, there is not static routing / protocol implemented just serial interface with ppp encapsulation link brought up .   if you try to ping the R1 interface ip 192.168.100.1  from R2 interface ip 192.168.1.1 will it succeed ? R2#ping 192.168.100.1 Lets check the router interface: R1#show run int s1/0 Building configuration... Current configuration : 160 bytes ! interface Serial1/0 ip address 192.168.200.1 255.255.255.0 secondary ip address 192.168.100.1 255.255.255.0 encapsulation ppp serial restart-delay 0 R2#show run int s1/0 Building configuration... Current configuration : 110 bytes ! interface Serial1/0 ip address 192.168.1.1 255.255.255.254 encapsulation ppp serial restart-delay 0 end Answer is Yes you can ping. R2#ping 192.168.100.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.100.1, ti...

Can we assign /31 address on the point to point link & save 50 % of ip address?  Answer is yes. R2(config)#int fa0/0 R2(config-if)#ip address 192.168.1.0 255.255.255.254 % Warning: use /31 mask on non point-to-point interface cautiously R4(config)#int fa0/0 R4(config-if)#ip address 192.168.1.1 255.255.255.254 % Warning: use /31 mask on non point-to-point interface cautiously Let’s try to ping :) R4#ping 192.168.1.0 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.1.0, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms Ok do we need privilege mode to ping ? no . R4> ping 192.168.1.0 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.1.0, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms Let’s check the ip route: R4#show ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP...