To determine if two hosts can communicate directly, their IP addresses must:
Belong to the same subnet
Have matching subnet boundaries (based on their masks)
Let’s evaluate each:
A. 192.168.17.15/29 → Subnet: 192.168.17.8 – 192.168.17.15
192.168.17.20/28 → Subnet: 192.168.17.16 – 192.168.17.31
→ Different subnets →❌
B. 10.5.5.1/24 → Subnet: 10.5.5.0 – 10.5.5.255
10.5.5.100/25 → Subnet: 10.5.5.0 – 10.5.5.127
→ Different masks → Host with /25 may treat others outside /25 as unreachable →❌
C. 10.10.0.17/22 → Range: 10.10.0.0 – 10.10.3.255
10.10.1.30/23 → Range: 10.10.0.0 – 10.10.1.255
→ Both addresses fall within same larger /22 range →✅
D. 192.168.0.5/26 → Subnet: 192.168.0.0 – 192.168.0.63
192.168.0.100 → Not enough info; assume default /24
→ /26 and /24 will not overlap fully → likely unreachable →❌
MTCNA Course Manual – IP Subnetting:
“Hosts can communicate directly if they are in the same IP range and have the same subnet mask. Different subnet boundaries require routing.”
René Meneses Guide – Mask Comparison:
“Be cautious of overlapping address ranges. Matching IPs in same range with differing subnet masks may fail to communicate.”
Terry Combs Notes – Direct Connectivity Rules:
“Same subnet mask and same address block = direct communication. If masks differ, communication needs a router.”
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