In my home network, 192.168.1.0/24. I ping all pcs and received TTL=128, but except 1 PC (XP1), I got TTL=64.
The PC(XP1) is able to access other PC and has the access to internet as well.

Pinging 192.168.1.5 with 32 bytes of data:

Reply from 192.168.1.5: bytes=32 time<1ms TTL=64
Reply from 192.168.1.5: bytes=32 time<1ms TTL=64
Reply from 192.168.1.5: bytes=32 time<1ms TTL=64
Reply from 192.168.1.5: bytes=32 time<1ms TTL=64

Ping statistics for 192.168.1.5:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms


Can anyone tell me why this PC has TTL=64? I think it should be TTL=128 for XP
machine...

While I don't think having a Time To Live (TTL) value of 64 will cause any problems whatsoever, your question was why this one PC has this setting.

The TTL value is stored in the registry (warning: dangerous territory) and can be changed (again warning!).

The default TTL for XP is 128, so something did change it, but again, I don't believe this will cause you any problems.

Refer to this article (http://support.microsoft.com/kb/314053) for more info.

In lieu of editting the registry directly (very dangerous), you might download SpeedGuide's TCP Optimizer (http://www.speedguide.net/downloads.php) program.

Best of luck,
WallyH