ICMP Fragmentation needed抓包实例

0000   e0 be 03 92 27 52 f8 98 ef a3 69 be 08 00 45 c0
0010   02 40 d7 42 00 00 3f 01 79 d1 c0 a8 d5 c9 c0 a8
0020   d0 ce 03 04 15 c8 00 00 05 c4 45 00 06 f2 cb bb
0030   40 00 7f 06 60 56 c0 a8 d0 ce 0d 6b 2a 12 e8 dd
0040   01 bb 8b 7e f5 38 15 ef c8 8a 50 18 04 02 cf d8
0050   00 00 16 03 01 06 c5 01 00 06 c1 03 03 40 97 08
0060   a6 fd e0 3b 38 76 fb 8b 72 f5 36 62 8e 1c df 17
0070   60 9e f3 2c 71 c2 72 b1 44 71 9a 77 db 20 d5 32
0080   7c 30 38 31 4a b8 56 2f bb ac dd 64 a9 74 6b ab
0090   ac e2 fb 8c c9 61 b2 45 41 41 bb 36 08 09 00 20
00a0   fa fa 13 01 13 02 13 03 c0 2b c0 2f c0 2c c0 30
00b0   cc a9 cc a8 c0 13 c0 14 00 9c 00 9d 00 2f 00 35
00c0   01 00 06 58 ea ea 00 00 00 23 00 00 00 10 00 0e
00d0   00 0c 02 68 32 08 68 74 74 70 2f 31 2e 31 44 69
00e0   00 05 00 03 02 68 32 fe 0d 00 ba 00 00 01 00 01
00f0   0f 00 20 f1 6d 43 8f 30 02 8e 6e 7a 27 f8 dc cf
0100   91 6e d3 7b 1b fe 4d d8 a9 3d e2 ad c0 bd 57 8b
0110   a5 80 1e 00 90 fc a6 c5 6f 5e f0 ea ad 8f 04 72
0120   03 c9 5e 89 ed 18 67 2f 98 b3 55 94 f7 b2 94 2e
0130   d6 5a 24 73 ae ed ce 07 7c d5 53 b2 3a 3b b7 4b
0140   86 15 80 35 f4 46 fc 84 48 55 a7 0a c5 e0 d0 a9
0150   d4 0e d6 da 27 81 2d 13 90 05 6f 70 b5 72 4d 35
0160   e3 37 44 5e 24 45 6b 12 2a c4 72 27 ce 13 4b ed
0170   36 e4 81 f0 8e 09 6a c4 de 68 88 37 73 11 fd 3a
0180   41 74 5d c1 4a 42 da 6e 38 21 3b e2 3b bc cb 5b
0190   ac 7e d2 cd 48 57 7b af c8 bc 0f e9 f7 67 bc 87
01a0   07 e0 5d d0 83 00 1b 00 03 02 00 02 00 05 00 05
01b0   01 00 00 00 00 00 2b 00 07 06 2a 2a 03 04 03 03
01c0   00 0a 00 0c 00 0a 5a 5a 63 99 00 1d 00 17 00 18
01d0   00 0b 00 02 01 00 00 17 00 00 00 00 00 21 00 1f
01e0   00 00 1c 6d 61 72 6b 65 74 70 6c 61 63 65 2e 76
01f0   69 73 75 61 6c 73 74 75 64 69 6f 2e 63 6f 6d ff
0200   01 00 01 00 00 12 00 00 00 33 04 ef 04 ed 5a 5a
0210   00 01 00 63 99 04 c0 08 cc 05 03 02 45 27 64 23
0220   52 62 9b 25 14 b2 d4 bd e4 96 4f f6 65 07 e9 ee
0230   a7 db 86 bd c4 f8 61 f8 a1 42 e2 08 a2 44 a3 a4
0240   6a 27 aa ac 10 c3 9b 30 7a d1 49 c3 52 61      


Frame 23176: 590 bytes on wire (4720 bits), 590 bytes captured (4720 bits) on interface \Device\NPF_{7FCA93D6-9836-4A47-95B7-BC82C4AB4747}, id 0
Ethernet II, Src: HuaweiTechno_a3:69:be (f8:98:ef:a3:69:be), Dst: LiteOnNetwor_92:27:52 (e0:be:03:92:27:52)
Internet Protocol Version 4, Src: 192.168.213.201, Dst: 192.168.208.206
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0xc0 (DSCP: CS6, ECN: Not-ECT)
        1100 00.. = Differentiated Services Codepoint: Class Selector 6 (48)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 576
    Identification: 0xd742 (55106)
    000. .... = Flags: 0x0
        0... .... = Reserved bit: Not set
        .0.. .... = Don't fragment: Not set
        ..0. .... = More fragments: Not set
    ...0 0000 0000 0000 = Fragment Offset: 0
    Time to Live: 63
    Protocol: ICMP (1)
    Header Checksum: 0x79d1 [validation disabled]
    [Header checksum status: Unverified]
    Source Address: 192.168.213.201
    Destination Address: 192.168.208.206
    [Stream index: 8]
Internet Control Message Protocol
    Type: 3 (Destination unreachable)
    Code: 4 (Fragmentation needed)
    Checksum: 0x15c8 [correct]
    [Checksum Status: Good]
    Unused: 0000
    MTU of next hop: 1476
    Internet Protocol Version 4, Src: 192.168.208.206, Dst: 13.107.42.18
        0100 .... = Version: 4
        .... 0101 = Header Length: 20 bytes (5)
        Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
            0000 00.. = Differentiated Services Codepoint: Default (0)
            .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
        Total Length: 1778
        Identification: 0xcbbb (52155)
        010. .... = Flags: 0x2, Don't fragment
            0... .... = Reserved bit: Not set
            .1.. .... = Don't fragment: Set
            ..0. .... = More fragments: Not set
        ...0 0000 0000 0000 = Fragment Offset: 0
        Time to Live: 127
        Protocol: TCP (6)
        Header Checksum: 0x6056 [validation disabled]
        [Header checksum status: Unverified]
        Source Address: 192.168.208.206
        Destination Address: 13.107.42.18
        [Stream index: 25]
    Transmission Control Protocol, Src Port: 59613, Dst Port: 443, Seq: 2340353336, Ack: 368035978
        Source Port: 59613
        Destination Port: 443
        Sequence Number: 2340353336
        [Stream index: 33]
        [Stream Packet Number: 6]
        [Conversation completeness: Complete, WITH_DATA (47)]
            ..1. .... = RST: Present
            ...0 .... = FIN: Absent
            .... 1... = Data: Present
            .... .1.. = ACK: Present
            .... ..1. = SYN-ACK: Present
            .... ...1 = SYN: Present
            [Completeness Flags: R·DASS]
        Acknowledgment Number: 368035978    (relative ack number)
        Acknowledgment number (raw): 368035978
        0101 .... = Header Length: 20 bytes (5)
        Flags: 0x018 (PSH, ACK)
            000. .... .... = Reserved: Not set
            ...0 .... .... = Accurate ECN: Not set
            .... 0... .... = Congestion Window Reduced: Not set
            .... .0.. .... = ECN-Echo: Not set
            .... ..0. .... = Urgent: Not set
            .... ...1 .... = Acknowledgment: Set
            .... .... 1... = Push: Set
            .... .... .0.. = Reset: Not set
            .... .... ..0. = Syn: Not set
            .... .... ...0 = Fin: Not set
            [TCP Flags: ·······AP···]
        Window: 1026
        [Calculated window size: 1026]
        [Window size scaling factor: 256]
        Checksum: 0xcfd8 [unverified]
        [Checksum Status: Unverified]
        Urgent Pointer: 0
        [Timestamps]
            [Time since first frame in this TCP stream: 0.061379000 seconds]
            [Time since previous frame in this TCP stream: 0.000411000 seconds]
        TCP payload (508 bytes)
    Transport Layer Security
        TLS segment data (508 bytes)

IPv4 以太网最小MTU是576，故当包设置不分片并且超过交换机最大MTU时会响应ICMP Fragmentation needed报文。
并且响应的报文最大字节是576，组成内容为 IP头部(20) + ICMP头部(8) + 不分片包的IP头部(20) + 不分片包的TCP头部(20) + 不分片包的剩余数据(508)