# R3 R1 R2 7 hosts LAN-2 17 hosts LAN-3 R3 R1 R2 3 hosts LAN-1 Give IP –addresses to the networks below with three point-to-point networks and three local.

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R3 R1 R2 7 hosts LAN-2 17 hosts LAN-3 R3 R1 R2 3 hosts LAN-1 Give IP –addresses to the networks below with three point-to-point networks and three local area networks. The available address space is 10.38.161.0 – 10.38.161.67 and the interface of R3 router towards LAN-3 is 10.38.161.1. 10.38.161.1

SOLUTION: 1. Find the point-to-points networks and the local networks. 2. Define the address space needed in each network (how many interfaces?) 3. What is the size of the block (power of 2)? 4. Start allocating the IP –addresses from R3 (10.38.100.1). 5. What is the mask? 6. Remember the rule: network address/number of addresses in the network = Interger Remarks: Address 10.38.100.12/28 (or 255.255.255.240) cannot be a network address. Why not? How to calculate the network address and broadcast address?

R3 R1 R2 3 hosts7 hosts 17 hosts SOLUTION 1. Find the point-to-points networks and the local networks. LAN-1 LAN-3 LAN-2 R1-R2 R1-R3 R2-R3

SOLUTION 2. Define the address space needed in each network (how many interfaces?) 3. What is the size of the block (power of 2)? LAN-3: 17 hosts+NWA+BCA+R3-interface=20  32 addr (5 bits) LAN-2: 7 hosts+1+1+1=10  16 addr (4 bits) LAN-1: 3 hosts+1+1+1=6  8 addr (3 bits) R1-R2: 2 hosts+1+1=4  4 addr (2 bits) R1-R3: 2+1+1=4  4 addr (2 bits) R2-R3: 2+1+1=4  4 addr (2 bits) 0 31|32 47|48 55|56 59|60 63|64 67| 32 addresses 16 addr 8 addr 4 a. 4 a. 4 a.

Address 10.38.100.12/28 (or 255.255.255.240) cannot be a network address. Why not? Mask=28  28 bits for network  32-28=4 bits for hosts  16 addr NWA/addresses  12/16 NOT Integer

10.38.100.12/28 = 10.38.100.12/255.255.255.240 00 0 0 11 0 0= 12 11 1 1 00 0 0= 240 mask 00 0 0 00 0 0= 0 NWA 00 0 0 11 1 1= INV mask How to calculate the network address and broadcast address? AND 00 0 0 11 1 1= 15 BCA OR

00 0 0 11 0 0= 12 00 0 0 11 0 1= 13 00 0 0 11 1 0= 14 00 0 0 11 1 1= 15 00 0 1 00 0 0= 16  needs 5 bits etc. Suppose we think that 12 is NWA and mask is 28. There are 4 bits available for hosts =16 addr (0  15).

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