i have the network topology in the diagram below. i was given the Internal address block of for assigning IP addresses.

Topology Diagram

Router 1 has a public ip address to the ISP

router 2 i assigned it the network which allows enough space for the 204 hosts

router 3 i assigned it the network which allows enough space for the 50 hosts

router 4 connected to r1 and frame relay.

router 6 i assigned it the 4 networks,,, which allows enough space for the 4 * 44 hosts networks.

router 5 i assigned it the 6 networks,, - which allows enough space for the 6 * 210 hosts networks.

my question is what ip addresses should i assign the serial ports of r1 - r2, r1 - r3, r1 - r4, etc. should i use another network( or use up free addresses in lets say the block like,, ?

what is good practice in this situation as i will be summarize the addresses for smaller routing tables.

the routing protocol i will be using will be OSPF.

R1 will be implementing Nat.


  • 1 is not a private network address
    – hertitu
    Commented Nov 9, 2016 at 16:27
  • i know but thats what we were given for the internal IP address of our assignment
    – Swannie
    Commented Nov 12, 2016 at 16:38

1 Answer 1


For point-to-point links, use a maximum size of /30. Depending on your model of router, it may support a subnet size of /31 which would be even better. Carve these small subnets out of your unused space. You can reserve a /24 network and use it only for p2p links, then take your smaller /30 /31 subnets from this space.

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