What is the smallest summary route that covers `10.1.100.0/24`, `10.1.101.0/24`, `10.1.102.0/24`, and `10.1.103.0/24`?

### Why this is right The four `/24` networks are contiguous and span third-octet values 100 through 103. That aligned group fits in one `/22` block beginning at `10.1.100.0`, making it the smallest listed summary that covers all four networks. ### The concept Route summarization combines multiple more-specific routes into a single less-specific route advertisement. A `/22` covers four consecutive `/24` networks when the block begins on the correct boundary. A `/16` also covers the four networks, but it covers far more addresses than these four routes. The network address must be aligned to the summary prefix for the summary to describe the intended block correctly. ### The other options - **B. `10.1.100.0/24`**: this covers only one of the four listed networks, so it is tempting as a matching prefix but incomplete. - **C. `10.1.0.0/16`**: this includes all four but is much broader than necessary. - **D. `10.1.100.0/30`**: this is a tiny block and cannot cover four `/24` networks. ### Worked numbers - **Given**: four contiguous `/24` networks, third-octet values 100, 101, 102, and 103. - **Find**: the smallest summary prefix. - **Formula**: four `/24` blocks combine into one `/22` block when aligned, because the block count is $2^{24-22}=4$. - **Solve**: the range 100 through 103 contains four consecutive `/24` networks; the aligned base is 100. - **Answer**: `10.1.100.0/22`. - **Check**: `/22` covers four `/24` blocks, matching the four routes. ### Terms - **IP**: Internet Protocol. The addressing system used to identify networks and hosts. ### Remember Summarize contiguous networks with the narrowest aligned prefix that covers them.