Ethereal-users: [Ethereal-users] IP Header Checksum 0x0000

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From: "Beasley, Alicia Ms CTR US DISA CDM2" <Alicia.Beasley@xxxxxxxxxxxx>
Date: Tue, 8 Aug 2006 10:21:56 -0500
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Ethereal,
    I am troubleshooting an issue involving a smtp connection from our exchange server on one network to an Ironport Mail Relay.  The problem is that email will start building up in the mail queue on the exchange server and during this time I don't see any packets traverse between the two devices on the network.  An ethereal capture taken on the exchange server itself shows one difference at the time right before the mail stops flowing.  I have attached three packets with 0x0000 IP header checksum. 
Can someone explain to me what this means?  After these three packets, there are no packets for about 60 seconds and then a new session starts and mail starts flowing again.
 
 
Alicia D. Beasley
Systems Analyst II
Central Communications Center (CCC)
DISA Montgomery
 
 
No.     Time        Source                Destination           Protocol Info
   1590 108.811255  x.x.x.x         y.y.y.y          TCP      29453 > smtp [SYN] Seq=0 Ack=0 Win=65535 Len=0 MSS=1460

Frame 1590 (62 bytes on wire, 62 bytes captured)
    Arrival Time: Aug  8, 2006 08:28:12.593030000
    Time delta from previous packet: 108.811255000 seconds
    Time since reference or first frame: 108.811255000 seconds
    Frame Number: 1590
    Packet Length: 62 bytes
    Capture Length: 62 bytes
    Protocols in frame: eth:ip:tcp
Ethernet II, Src: x.x.x.x (00:02:a5:4e:86:16), Dst: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Destination: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Source: x.x.x.x (00:02:a5:4e:86:16)
    Type: IP (0x0800)
Internet Protocol, Src: x.x.x.x (x.x.x.x), Dst: y.y.y.y (y.y.y.y)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 48
    Identification: 0x6981 (27009)
    Flags: 0x04 (Don't Fragment)
        0... = Reserved bit: Not set
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: TCP (0x06)
    Header checksum: 0x0000 [incorrect, should be 0xa442]
    Source: x.x.x.x (x.x.x.x)
    Destination: y.y.y.y (y.y.y.y)
Transmission Control Protocol, Src Port: 29453 (29453), Dst Port: smtp (25), Seq: 0, Ack: 0, Len: 0
    Source port: 29453 (29453)
    Destination port: smtp (25)
    Sequence number: 0    (relative sequence number)
    Header length: 28 bytes
    Flags: 0x0002 (SYN)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...0 .... = Acknowledgment: Not set
        .... 0... = Push: Not set
        .... .0.. = Reset: Not set
        .... ..1. = Syn: Set
        .... ...0 = Fin: Not set
    Window size: 65535
    Checksum: 0x491f [correct]
    Options: (8 bytes)
        Maximum segment size: 1460 bytes
        NOP
        NOP
  
 SACK permitted
***********************************************

No.     Time        Source                Destination           Protocol Info
   1601 111.692413  x.x.x.x         y.y.y.y          TCP      29453 > smtp [SYN] Seq=0 Ack=0 Win=65535 Len=0 MSS=1460

Frame 1601 (62 bytes on wire, 62 bytes captured)
    Arrival Time: Aug  8, 2006 08:28:15.474188000
    Time delta from previous packet: 2.881158000 seconds
    Time since reference or first frame: 111.692413000 seconds
    Frame Number: 1601
    Packet Length: 62 bytes
    Capture Length: 62 bytes
    Protocols in frame: eth:ip:tcp
Ethernet II, Src: x.x.x.x (00:02:a5:4e:86:16), Dst: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Destination: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Source: x.x.x.x (00:02:a5:4e:86:16)
    Type: IP (0x0800)
Internet Protocol, Src: x.x.x.x (x.x.x.x), Dst: y.y.y.y (y.y.y.y)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 48
    Identification: 0x7373 (29555)
    Flags: 0x04 (Don't Fragment)
        0... = Reserved bit: Not set
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: TCP (0x06)
    Header checksum: 0x0000 [incorrect, should be 0x9a50]
    Source: x.x.x.x (x.x.x.x)
    Destination: y.y.y.y (y.y.y.y)
Transmission Control Protocol, Src Port: 29453 (29453), Dst Port: smtp (25), Seq: 0, Ack: 0, Len: 0
    Source port: 29453 (29453)
    Destination port: smtp (25)
    Sequence number: 0    (relative sequence number)
    Header length: 28 bytes
    Flags: 0x0002 (SYN)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...0 .... = Acknowledgment: Not set
        .... 0... = Push: Not set
        .... .0.. = Reset: Not set
        .... ..1. = Syn: Set
        .... ...0 = Fin: Not set
    Window size: 65535
    Checksum: 0x491f [correct]
    Options: (8 bytes)
        Maximum segment size: 1460 bytes
        NOP
        NOP
        SACK permitted


*******************************************
No.     Time        Source                Destination           Protocol Info
   1622 117.699396  x.x.x.x         y.y.y.y          TCP      29453 > smtp [SYN] Seq=0 Ack=0 Win=65535 Len=0 MSS=1460

Frame 1622 (62 bytes on wire, 62 bytes captured)
    Arrival Time: Aug  8, 2006 08:28:21.481171000
    Time delta from previous packet: 6.006983000 seconds
    Time since reference or first frame: 117.699396000 seconds
    Frame Number: 1622
    Packet Length: 62 bytes
    Capture Length: 62 bytes
    Protocols in frame: eth:ip:tcp
Ethernet II, Src: x.x.x.x (00:02:a5:4e:86:16), Dst: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Destination: All-HSRP-routers_06 (00:00:0c:07:ac:06)
    Source: x.x.x.x (00:02:a5:4e:86:16)
    Type: IP (0x0800)
Internet Protocol, Src: x.x.x.x (x.x.x.x), Dst: y.y.y.y (y.y.y.y)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 48
    Identification: 0x8d01 (36097)
    Flags: 0x04 (Don't Fragment)
        0... = Reserved bit: Not set
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: TCP (0x06)
    Header checksum: 0x0000 [incorrect, should be 0x80c2]
    Source: x.x.x.x (x.x.x.x)
    Destination: y.y.y.y (y.y.y.y)
Transmission Control Protocol, Src Port: 29453 (29453), Dst Port: smtp (25), Seq: 0, Ack: 0, Len: 0
    Source port: 29453 (29453)
    Destination port: smtp (25)
    Sequence number: 0    (relative sequence number)
    Header length: 28 bytes
    Flags: 0x0002 (SYN)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...0 .... = Acknowledgment: Not set
        .... 0... = Push: Not set
        .... .0.. = Reset: Not set
        .... ..1. = Syn: Set
        .... ...0 = Fin: Not set
    Window size: 65535
    Checksum: 0x491f [correct]
    Options: (8 bytes)
        Maximum segment size: 1460 bytes
        NOP
        NOP
        SACK permitted

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