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標(biāo)題: 共享網(wǎng)卡是怎么路由的 [打印本頁]

作者: xieShell 時(shí)間: 2008-11-28 21:24
標(biāo)題: 共享網(wǎng)卡是怎么路由的
我的網(wǎng)絡(luò)結(jié)構(gòu)是這樣的：
                              INTERNET
                                    |
                                    |
   A：192.168.1.1/24 -- HUB -- B：192.168.1.2/24
         222.65.*.*
A是我的WINDOWS電腦，它直接連在INTERNET上，有個(gè)公網(wǎng)IP和一個(gè)私網(wǎng)IP，我把它的網(wǎng)卡設(shè)成共享了。B是我另一臺(tái)電腦，它與A用HUB連接，它只有一個(gè)私網(wǎng)IP。A與B的私網(wǎng)IP是在一個(gè)網(wǎng)段里的。B的網(wǎng)關(guān)我設(shè)成了A的私網(wǎng)地址，這樣，B就能訪問公網(wǎng)了。
我用WIRKSHARK抓了A網(wǎng)卡上的包。想了解A是根據(jù)什么來路由B的包的。

這里，A的私網(wǎng)IP是192.168.1.1/24，公網(wǎng)IP是222.65.*.*，MAC地址是00:30:18:aa:3a:cc
B的私網(wǎng)IP是192.168.1.2/24，MAC地址是00:0c:29:b3:a7:76

我抓了B PING百度的包，

No.    Time       Source             Destination          Protocol Info
1    18.926754 192.168.1.2          203.208.*.*       ICMP    Echo (ping) request
Frame 31 (98 bytes on wire, 98 bytes captured)
Ethernet II, Src: 00:0c:29:b3:a7:76, Dst: 00:30:18:aa:3a:cc
Internet Protocol, Src: 192.168.1.2 (192.168.1.2), Dst: 203.208.*.* (203.208.*.*)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 84
Identification: 0x0000 (0)
Flags: 0x04 (Don't Fragment)
Fragment offset: 0
Time to live: 64
Protocol: ICMP (0x01)
Header checksum: 0x85c6 [correct]
Source: 192.168.1.2 (192.168.1.2)
Destination: 203.208.*.* (203.208.*.*)
Internet Control Message Protocol
Type: 8 (Echo (ping) request)
Code: 0 ()
Checksum: 0x4da5 [correct]
Identifier: 0x0a0b
Sequence number: 2 (0x0002)
Data (56 bytes)

No.    Time       Source             Destination          Protocol Info
2    18.926870 222.65.*.*       203.208.*.*       ICMP    Echo (ping) request
Frame 32 (106 bytes on wire, 106 bytes captured)
Ethernet II, Src: 00:30:18:aa:3a:cc, Dst: 00:90:1a:41:d5:6e
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol, Src: 222.65.*.* (222.65.*.*), Dst: 203.208.*.* (203.208.*.*)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 84
Identification: 0x0000 (0)
Flags: 0x04 (Don't Fragment)
Fragment offset: 0
Time to live: 63
Protocol: ICMP (0x01)
Header checksum: 0xf079 [correct]
Source: 222.65.*.* (222.65.*.*)
Destination: 203.208.*.* (203.208.*.*)
Internet Control Message Protocol
Type: 8 (Echo (ping) request)
Code: 0 ()
Checksum: 0x56b0 [correct]
Identifier: 0x0100
Sequence number: 2 (0x0002)
Data (56 bytes)

No.    Time       Source             Destination          Protocol Info
3    19.066742 203.208.*.*       222.65.*.*       ICMP    Echo (ping) reply
Frame 33 (106 bytes on wire, 106 bytes captured)
Ethernet II, Src: 00:90:1a:41:d5:6e, Dst: 00:30:18:aa:3a:cc
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol, Src: 203.208.*.* (203.208.*.*), Dst: 222.65.*.* (222.65.*.*)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 84
Identification: 0x0000 (0)
Flags: 0x04 (Don't Fragment)
Fragment offset: 0
Time to live: 246
Protocol: ICMP (0x01)
Header checksum: 0x3979 [correct]
Source: 203.208.*.* (203.208.*.*)
Destination: 222.65.*.* (222.65.*.*)
Internet Control Message Protocol
Type: 0 (Echo (ping) reply)
Code: 0 ()
Checksum: 0x5eb0 [correct]
Identifier: 0x0100
Sequence number: 2 (0x0002)
Data (56 bytes)

No.    Time       Source             Destination          Protocol Info
4    19.068816 203.208.*.*       192.168.1.2          ICMP    Echo (ping) reply
Frame 34 (98 bytes on wire, 98 bytes captured)
Ethernet II, Src: 00:30:18:aa:3a:cc, Dst: 00:0c:29:b3:a7:76
Internet Protocol, Src: 203.208.*.* (203.208.*.*), Dst: 192.168.1.2 (192.168.1.2)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 84
Identification: 0x0000 (0)
Flags: 0x04 (Don't Fragment)
Fragment offset: 0
Time to live: 245
Protocol: ICMP (0x01)
Header checksum: 0xd0c5 [correct]
Source: 203.208.*.* (203.208.*.*)
Destination: 192.168.1.2 (192.168.1.2)
Internet Control Message Protocol
Type: 0 (Echo (ping) reply)
Code: 0 ()
Checksum: 0x55a5 [correct]
Identifier: 0x0a0b
Sequence number: 2 (0x0002)
Data (56 bytes)

這里，第1和第2個(gè)包是PING出去的包，A的網(wǎng)卡收到B發(fā)來的包后，把包的源IP翻譯成自己的IP，源MAC地址翻譯成自己的MAC地址，再轉(zhuǎn)發(fā)到公網(wǎng)上；收到回的PING包后，同樣，把目的MAC和IP地址翻譯成B網(wǎng)卡的，轉(zhuǎn)發(fā)給B。現(xiàn)在的問題是，我從包的IP層沒法找到能用來標(biāo)記需要轉(zhuǎn)發(fā)的標(biāo)記。

請(qǐng)高人指點(diǎn)，A收到包后根據(jù)那個(gè)部分來識(shí)別這個(gè)包是需要轉(zhuǎn)發(fā)的。

作者: luffy.deng 時(shí)間: 2008-11-29 13:36
根據(jù)包的目的地址

作者: nicecat 時(shí)間: 2008-11-30 00:46
LZ問的大概是送回來的包怎么找回原主機(jī)的吧

作者: xieShell 時(shí)間: 2008-11-30 11:21

原帖由 nicecat 于 2008-11-30 00:46 發(fā)表
LZ問的大概是送回來的包怎么找回原主機(jī)的吧

是的，請(qǐng)指教啊

[ 本帖最后由 xieShell 于 2008-11-30 11:25 編輯 ]

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