Secure Point-to-Point IP Addressing

Nerd Cafe | نرد کافه

Step 1: Understand the topology

We have:

• You want to assign addresses in the 10.0.0.0/x range.

• This is a point-to-point link, meaning only 2 devices exist on this subnet.

Step 2: Choose the subnet mask

• Normally, a subnet mask defines the number of hosts.

• On a point-to-point link, we only need 2 IPs.

• The smallest subnet mask to allow 2 usable hosts is /30.

Calculation:

• /30 → 32 − 30 = 2 host bits

• Hosts = 2² − 2 = 2 usable IPs, Perfect for point-to-point.

Subnet: 10.0.0.0/30

• Network address: 10.0.0.0

• Usable IPs: 10.0.0.1 and 10.0.0.2

• Broadcast: 10.0.0.3

Step 3: Assign IP addresses

• R1 Serial interface: 10.0.0.1/30

• R2 Serial interface: 10.0.0.2/30

Step 4: Cisco configuration

On R1:

R1> enable
R1# configure terminal
R1(config)# interface serial0/0/0
R1(config-if)# ip address 10.0.0.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# exit

On R2:

R2> enable
R2# configure terminal
R2(config)# interface serial0/0/0
R2(config-if)# ip address 10.0.0.2 255.255.255.252
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# exit

Step 5: Test connectivity

From R1:

R1# ping 10.0.0.2

• If successful, the link is up.

Step 6: Security advantage

• Using /30:

  • Limits IP addresses to exactly two usable hosts, preventing extra devices from joining.

  • Minimizes attack surface on the link.

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Keywords

Network IP , Broadcast IP , First IP (usable) , Last IP (usable) , Number of available IPs (hosts) , Subnet mask , Nerd Cafe , نرد کافه

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