If the default gateway address is incorrectly configured on a host, the host will not be able to communicate with devices outside its local network. This means it cannot access the internet or other remote networks. However, the host can still communicate with other devices within the same local network. The incorrectly configured default gateway prevents proper routing of packets destined for external networks, but local network communication remains unaffected. Key consequences include:

• No internet or remote network access.
• Local network communication remains possible.
• The host will not know the correct path to send packets outside the local network.
• Network performance and connectivity issues may arise when trying to reach external networks.

Some misinformation includes claims that a ping to 127.0.0.1 (loopback) would fail or that local communication would be impacted; these are incorrect. Pinging 127.0.0.1 tests the host's own network stack and is always successful regardless of gateway issues. Also, local network communication does not require a default gateway and is based on MAC addresses handled by switches. In summary, the critical impact of a wrong default gateway is the inability to reach other networks beyond the local subnet, thereby cutting off internet or extranet access.