網路工程考題

某IP封包其前面幾個欄位內容以16進位表示為:

45000058000100001706.......

則此封包還可以經過幾個路由器,而不會被丟棄

1 Answer

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  • FISH
    Lv 4
    1 decade ago
    Favorite Answer

    表頭

    4:0100 板本

    5:0101 header length fiedl=5 * 32 =160bit

    00 : 0000 0000

    bits 0-2: precedence

    bit 3: 0 = Normal Delay, 1 = Low Delay

    bit 4: 0 = Normal Throughput, 1 = High Throughput

    bit 5: 0 = Normal Reliability, 1 = High Reliability

    bits 6-7: Reserved for future use

    0058 : Total Length(datagram size)

    0000 0000 0101 1000 = 64+16+8=58Bytes

    0001 : Identification

    0000 : (000) 000 0000 0000 =(Flags)+Fragment Offset

    Fragment Offset

    This allows a maximum offset of 65,528 () which would exceed the maximum IP packet length of 65,535 with the header length included.

    17 : Time To Live (TTL)

    0001 0111 = 32+4+2+1=39

    所以剩16個count

    06 : Protocol 0000 0110

    說了一堆其實那些16進位要一個個化成二進位會更好懂

    其實要看TTL就次從NO.64bit ~ 72 bit來看

    化成二進位加總就好了最高是255

    2008-03-08 10:22:45 補充:

    更正內容 :

    -----------------------------------

    17 : Time To Live (TTL)

    0001 0111 = 32+4+2+1=39

    所以剩16個count

    -----------------------------------

    上面0001 0111的二進位加總是23

    因此應該剩23個cunt

    2008-03-08 12:08:43 補充:

    好笑的是...我還寫成32+4+2+1......

    應該是16+4+2+1......

    一題兩笨點我應該要去po笨版了...

    Source(s): 門市工程師
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