Why is the TTL for a loopback (127.0.0.1) 128 seconds, and yet it is
relatively small (48 seconds) for others?
The default TTL for all traffic in Windows 2000 (and most recent Windows OSs) is 128, regardless of the interface used. However, any application can override that default when sending packets. For example, PING sets the TTL to 32 by default. So, if you're seeing traffic with a TTL of 48, the application probably overrode the default.
You can change the default by modifying this registry value:
This was first published in November 2001