Computer Networks · M2 · mocks

Q3 · Find the complete /27 block

M2 mock A

Q1(a)+Q1(b) compulsory; choose any two of Q2/Q3/Q4 · 10 marks attempted

Question. Find the network address, broadcast address and usable host range of 192.168.5.197/27. [3 practice marks]

Answer

Given

IP/prefix = 192.168.5.197/27.

To find

The complete containing address block and its usable host range.

Formula and why

h=32-p,\qquad N=2^hLaTeX: h=32-p,\qquad N=2^h
\text{step}=256-\text{changing mask octet}LaTeX: \text{step}=256-\text{changing mask octet}

Use the explicit prefix. We show both the interval method and bitwise AND so the boundary can be understood.

Step-by-step solution

Step 1. Count host bits and addresses

h=32−27=5; N=25=32.

Step 2. Construct the mask

Mask=255.255.255.224; binary=11111111.11111111.11111111.11100000.

Step 3. Find the changing-octet interval

The changing octet is number 4. Its mask value is 224, so step=256−224=32. The IP value 197 lies in 192…223.

Step 4. Form the first/network address

Keep earlier octets; place 192 in octet 4; set any later octets to zero. Network=192.168.5.192.

Step 5. Show the AND operation

OctetIP bitsMask bitsAND resultDecimal
1110000001111111111000000192
2101010001111111110101000168
30000010111111111000001015
4110001011110000011000000192

Step 6. Form the last/broadcast address

Use 223 in the changing octet and 255 in any later octets. Broadcast=192.168.5.223.

Step 7. State usable hosts

First usable=192.168.5.193; last usable=192.168.5.222; count=32−2=30.

Final answer: Network 192.168.5.192; broadcast 192.168.5.223; 32 total, 30 ordinary usable; range 192.168.5.193–192.168.5.222.