Database Reference
In-Depth Information
In the preceding output,
time to live
is set to 64. If all IP packets needed to reassemble a segment are
not received in about 60 seconds, then segment transmission is declared as lost and all packets with the same
identification are thrown away.
The following section shows the actual contents of the data itself. Each 1,500-byte packet has a payload of about
1,480 bytes.
Data (1480 bytes)
0000 50 97 f5 c1 20 90 2c 9f 04 03 02 01 22 7b 14 00 P... .,....."{..
0010 00 00 00 00 4d 52 4f 4e 00 03 00 00 00 00 00 00 ....MRON........
0020 8c 5e fd 2b 20 02 00 00 94 20 ed 2a 1c 00 00 00 .^.+ .... .*....
Five more packets are received and printed by the Wireshark tool. Frame 52 starts at an offset of 1480. So, the first
packet starts at an offset of 0 and the second packet has an offset of 1,480 bytes; this offset will be used by kernel to
reassemble the buffer.
Frame 52 (1514 bytes on wire, 1514 bytes captured)
...
Identification: 0x533e (21310)
...
Fragment offset: 1480
Time to live: 64
Protocol: UDP (0x11)
The last packet in this series of packets is important, as it shows how reassembly is performed.
Frame 56
is the
last packet with a size of 970 bytes and a payload of 936 bytes.
More fragments
bit is not set, indicating that there are
no more fragments to receive.
Frame 56 (970 bytes on wire, 970 bytes captured)
...
Total Length: 956
Identification: 0x533e (21310)
Flags: 0x00
0... = Reserved bit: Not set
.0.. = Don't fragment: Not set
..0. = More fragments: Not set
Output printed by Wireshark for the last packet shows various IP fragments as a summary. This summary
shows that five packets with a payload of 1,480 bytes each and a sixth packet with a payload of 936 bytes were received.
These six fragments assemble together to create one UDP buffer of size 8,336 bytes, which is essentially one 8K block
plus header information for the cache fusion traffic.
[IP Fragments (8336 bytes): #51(1480), #52(1480), #53(1480), #54(1480), #55(1480), #56(936)]
[Frame: 51, payload: 0-1479 (1480 bytes)]
[Frame: 52, payload: 1480-2959 (1480 bytes)]
[Frame: 53, payload: 2960-4439 (1480 bytes)]
[Frame: 54, payload: 4440-5919 (1480 bytes)]
[Frame: 55, payload: 5920-7399 (1480 bytes)]
[Frame: 56, payload: 7400-8335 (936 bytes)]
