ICMP l l l Echo Request Echo Reply
- Slides: 32
常見的ICMP類型 l l l Echo Request / Echo Reply(要求與回應) Destination Unreachable(無法到達目的) Source Quench(降低來源端傳輸速度) Redirect(重新導向) Time Exceeded(逾時)
Echo Request / Echo Reply(要求與回應) l 封包欄位 l ICMP表頭
Echo Request / Echo Reply(要求與回應) l ICMP資料的三個欄位: l l Identifier:長度為 2 Bytes,做為識別之用,由Echo Request來 源端裝置的程式所決定。當目的端裝置收到Echo Request後, 所回應Echo. Reply的Identifier欄位值必須與收到的Echo Request相同。 Sequence Number:長度為 2 Bytes,用來記錄序號,由Echo Request來源端裝置的程式所決定。當目的端裝置收到Echo Request後,所回應Echo Reply的Sequence Number欄位值必須 與收到的Echo Request相同,如此Identifier與Sequence Number兩個欄位合起來,可識別特定配對的Echo Request / Echo Reply。
Echo Request / Echo Reply(要求與回應) l Optional Data:長度不定,由Echo Request來源端裝 置的程式所決定,可記錄一些選擇性的資料。當目 的端裝置收到Echo Request後,所回應Echo Reply的 Optional Data欄位值必須與收到的Echo Request相同。 Echo Request來源端收到Echo Reply後,會讀取 Optional Data欄位值,確認此為配對的Echo Reply。
Destination Unreachable(無法到 達目的) l Code欄位值
Time Exceeded(逾時) l 封包欄位 l Code欄位值: l l 0:TTL count exceeded 1:Fragment reassembly time exceeded Unused:長 度為 4 Bytes,未定義用途,欄位內容必須為 0。
擷取ICMP封包(Echo request)
擷取ICMP封包(Echo request) l l l l 說明: Type = 8 (Echo Request) ,其十六進位為 08; Code = 0 (Not Used (MBZ)) ,其十六進位為 00; Check. Sum = 0 x 032 c(十六進位值); Indentified = 0 x 0200; Sequence Number = 62163,其十六進位為 0 xf 2 d 3; Data : [64 bytes]
擷取ICMP封包(Echo reply)
擷取ICMP封包(Echo reply) l l l l 說明: Type = 0 (Echo Reply) ,其十六進位為 00 ; Code = 0 (Not Used (MBZ)) ,其十六進位為 00; Check. Sum = 0 x 0 b 2 c(十六進位值); Indentified = 0 x 0200; Sequence Number = 62163 ,其十六進位為 0 xf 2 d 3; Data : [56 bytes];
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