Newsgroup: it.comp.os.linux.iniziare
Titolo: Header checksum: 0x0000 [incorrect, should be 0xc18a]

Salve.
Ho una macchina linux (kernel 2.4.32) e un server windows 2003.
Ho installato wireshark sul server windows. Poi dalla macchina linux
ho fatto una richiesta http (web server su porta 81, ma vale anche per
ping e tutto il resto) su tale server. sul pacchetto di ritorno
wireshark mi dice:
No.     Time        Source                Destination
Protocol Info
     48 26.459925   192.168.0.2           192.168.0.1
TCP      81 > 32873 [ACK] Seq=494 Ack=347 Win=65190 Len=0 TSV=1499690
TSER=50841679
Frame 48 (66 bytes on wire, 66 bytes captured)
    Arrival Time: Nov 12, 2009 12:04:33.518684000
    [Time delta from previous captured frame: 0.000014000 seconds]
    [Time delta from previous displayed frame: 0.000014000 seconds]
    [Time since reference or first frame: 26.459925000 seconds]
    Frame Number: 48
    Frame Length: 66 bytes
    Capture Length: 66 bytes
    [Frame is marked: False]
    [Protocols in frame: eth:ip:tcp]
    [Coloring Rule Name: Checksum Errors]
    [Coloring Rule String: cdp.checksum_bad==1 || edp.checksum_bad==1
|| ip.checksum_bad==1 || tcp.checksum_bad==1 || udp.checksum_bad==1 ||
mstp.checksum_bad==1]
Ethernet II, Src: Micro-St_10:6a:0f (00:21:85:10:6a:0f), Dst:
HewlettP_05:11:ef (00:16:35:05:11:ef)
Internet Protocol, Src: 192.168.0.2 (192.168.0.2), Dst: 192.168.0.1
(192.168.0.1)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN:
0x00)
    Total Length: 52
    Identification: 0xf903 (63747)
    Flags: 0x04 (Don't Fragment)
    Fragment offset: 0
    Time to live: 128
    Protocol: TCP (0x06)
    Header checksum: 0x0000 [incorrect, should be 0x806c]
    Source: 192.168.0.2 (192.168.0.2)
    Destination: 192.168.0.1 (192.168.0.1)
Transmission Control Protocol, Src Port: 81 (81), Dst Port: 32873
(32873), Seq: 494, Ack: 347, Len: 0
0000  00 16 35 05 11 ef 00 21 85 10 6a 0f 08 00 45 00   ..
5....!..j...E.
0010  00 34 f9 03 40 00 80 06 00 00 c0 a8 00 02 c0 a8   .
4..@...........
0020  00 01 00 51 80 69 31 9c 85 92 d3 36 be db 80
10   ...Q.i1....6....
0030  fe a6 7f 2f 00 00 01 01 08 0a 00 16 e2 2a 03
07   .../.........*..
0040  c8 4f                                             .O
Notare il
    Header checksum: 0x0000 [incorrect, should be 0x806c]
e me lo marca in rosso su nero.
mentre linux con "tcpdump -vv  -n src host 192.168.0.2 and src port
81"
12:03:29.648548 IP (tos 0x0, ttl 128, id 63732, offset 0, flags [DF],
proto: TCP (6), length: 64) 192.168.0.2.81 > 192.168.0.1.32873: S,
cksum 0xede9 (correct), 832340900:832340900(0) ack 
3543580033
 win
65535 <mss 1460,nop,wscale 0,nop,nop,timestamp 0 0,nop,nop,sackOK>
12:03:29.659256 IP (tos 0x0, ttl 128, id 63733, offset 0, flags [DF],
proto: TCP (6), length: 544) 192.168.0.2.81 > 192.168.0.1.32873: FP
1:493(492) ack 346 win 65190 <nop,nop,timestamp 1499659 50841376>
12:03:32.688687 IP (tos 0x0, ttl 128, id 63747, offset 0, flags [DF],
proto: TCP (6), length: 52) 192.168.0.2.81 > 192.168.0.1.32873: .,
cksum 0x7f2f (correct), 494:494(0) ack 347 win 65190
<nop,nop,timestamp 1499690 50841679>
Il pacchetto corrispondente a quello di cui sopra è l'ultimo, ma
wireshark mi da un output simile anche per gli altri due.
E' normale?
Ciao
Matteo

 E' normale?
Vedi un po'
http://wiki.wireshark.org/TCP_Checksum_Verification
Davide

Davide Bianchi wrote:

Ehm mi pare che il suo problema sia nell'header IP, non TCP.