On Oct 30, 2011, at 12:48 PM, Dale McCoy wrote:
> Unless I miss my guess, the pcap has timestamps stored in UTC.
Correct:
$ man pcap-savefile
PCAP-SAVEFILE(5) PCAP-SAVEFILE(5)
NAME
pcap-savefile - libpcap savefile format
DESCRIPTION
NOTE: applications and libraries should, if possible, use libpcap to
read savefiles, rather than having their own code to read savefiles.
If, in the future, a new file format is supported by libpcap, applica-
tions and libraries using libpcap to read savefiles will be able to
read the new format of savefiles, but applications and libraries using
their own code to read savefiles will have to be changed to support the
new file format.
...
Following the per-file header are zero or more packets; each packet
begins with a per-packet header, which is immediately followed by the
raw packet data. The format of the per-packet header is:
+---------------------------------------+
| Time stamp, seconds value |
+---------------------------------------+
| Time stamp, microseconds value |
+---------------------------------------+
| Length of captured packet data |
+---------------------------------------+
|Un-truncated length of the packet data |
+---------------------------------------+
All fields in the per-packet header are in the byte order of the host
writing the file. The per-packet header begins with a time stamp giv-
ing the approximate time the packet was captured; the time stamp con-
sists of a 4-byte value, giving the time in seconds since January 1,
1970, 00:00:00 UTC, followed by a 4-byte value, giving the time in
microseconds since that second. Following that are a 4-byte value giv-
ing the number of bytes of captured data that follow the per-packet
header and a 4-byte value giving the number of bytes that would have
been present had the packet not been truncated by the snapshot length.
The two lengths will be equal if the number of bytes of packet data are
less than or equal to the snapshot length.
> You can
> set Wireshark to display UTC timestamps, regardless of the local
> timezone, but I'm not aware of any way to force Wireshark to display
> any particular (other, i.e. non-zero) timezone offset.
On UN*X systems, you can run Wireshark with the TZ environment variable set to refer to the other time zone - note that a time zone may have more than just an offset, it may have an offset that changes over time, due to daylight savings time/summer time or due to the region changing its offset for other reasons.
