In binary notation, which pattern represents the first octet of a Class B IPv4 network address?

Introduction / Context:
Traditional classful IPv4 addressing divides addresses into classes A, B, C, and others based on the leading bits of the first octet. Although modern networks use classless addressing, understanding these patterns remains useful for historical questions and for quickly recognizing approximate address ranges.

Given Data / Assumptions:

• We are considering the first octet of an IPv4 address in binary.
• Class B addresses historically covered decimal values from 128 to 191.
• We must express this range as a bit pattern for the first eight bits.
• The x characters in the pattern represent either 0 or 1.

Concept / Approach:
An 8-bit octet can represent values from 0 to 255. Class B addresses start at 128 and end at 191. In binary, 128 is 10000000 and 191 is 10111111. The common prefix for all values in this range is 10, meaning that all Class B addresses begin with the bits 10 followed by six bits that can vary. Therefore, the general pattern for a Class B first octet is 10xxxxxx.

Step-by-Step Solution:
1. Recall the decimal range for Class B first octet values: 128 through 191.2. Convert 128 to binary: 10000000.3. Convert 191 to binary: 10111111.4. Observe that both values share the prefix bits 10 in the most significant positions.5. Replace the remaining six bits with x characters to indicate any combination, giving 10xxxxxx.

Verification / Alternative check:
You can quickly test a few values within the range, such as 130 or 150, and confirm that their binary representations also start with 10. Checking values outside the range, such as 110 or 200, shows different prefixes, confirming that only Class B addresses share the 10xxxxxx pattern.

Why Other Options Are Wrong:
Option A, 01xxxxxx, corresponds to decimal values roughly from 64 to 127, which are not Class B. Option B, 0xxxxxxx, covers values from 0 to 127 and mainly includes Class A ranges. Option D, 110xxxxx, describes the prefix for Class C addresses, which start at 192.

Common Pitfalls:
Learners sometimes reverse the mapping of bit patterns to classes or confuse Class B and Class C prefixes because both begin with 1. Remember the specific prefixes: 0 for Class A, 10 for Class B, and 110 for Class C in the first octet.

Final Answer:
10xxxxxx