Computer Networks · M2 · read

Exact route aggregation · example 3

CIDR, VLSM and route matching

Unit 4 · classless addressing

Practice question. Find a single exact CIDR aggregate for these networks: 172.16.8.0/23, 172.16.10.0/23. [3 practice marks]

Answer

Given

  • 172.16.8.0/23
  • 172.16.10.0/23

To find

One prefix covering exactly the same address range.

Formula and why

\text{total addresses}=\sum_i N_iLaTeX: \text{total addresses}=\sum_i N_i
p=32-\log_2(N)LaTeX: p=32-\log_2(N)

Adding sizes gives the candidate prefix. Contiguity and start-boundary alignment must also be satisfied.

Step-by-step solution

Step 1. Determine each block size

Each input block has 512 addresses.

Step 2. Add the address counts

2×512=1024.

Step 3. Find host bits and prefix

1024=210; prefix=32−10=/22.

Step 4. Verify the exact range

Inputs cover 172.16.8.0–172.16.11.255, without gaps. 172.16.8.0/22 covers the same start and end and is correctly aligned.

Final answer: 172.16.8.0/22