1、網(wǎng)絡(luò)拓?fù)?/strong>
網(wǎng)絡(luò)拓?fù)淙缦滤荆覀冊(cè)谶@里用到了三臺(tái)機(jī)子做實(shí)驗(yàn)，分別是①、④、⑦號(hào)機(jī)，使用①號(hào)機(jī)ping⑦號(hào)機(jī)，④號(hào)機(jī)作為路由轉(zhuǎn)發(fā)。
2、錯(cuò)誤的路由配置
首先我們使用如下的配置方法，配置這三臺(tái)機(jī)子的路由表：
1）在①號(hào)機(jī)種配置如下，讓目的網(wǎng)段是10.0.4.0/24的從eth1端口出去
route add -net 10.0.4.0/24 dev eth1
在①號(hào)機(jī)的查看路由表輸入如下命令：
route -n
①號(hào)機(jī)的路由表的結(jié)果如下：
2）在⑦號(hào)機(jī)使用同樣方法配置路由，結(jié)果如下：
3）在4號(hào)機(jī)配置路由轉(zhuǎn)發(fā)功能，即將/etc/sysctl.conf文件里面的net.ipv4.ip_forward的值置1：
4）所有的配置已經(jīng)完成，我們?cè)冖偬?hào)機(jī)ping④號(hào)機(jī)
ping 10.0.4.3
結(jié)果如下，即ping 不通：
PING 10.0.4.3 (10.0.4.3) 56(84) bytes of data.From 10.0.1.3 icmp_seq=2 Destination Host UnreachableFrom 10.0.1.3 icmp_seq=3 Destination Host UnreachableFrom 10.0.1.3 icmp_seq=4 Destination Host UnreachableFrom 10.0.1.3 icmp_seq=6 Destination Host UnreachableFrom 10.0.1.3 icmp_seq=7 Destination Host UnreachableFrom 10.0.1.3 icmp_seq=8 Destination Host Unreachable
這里為了方便研究，把①號(hào)機(jī)的eth1配置放出來(lái)
eth1 Link encap:Ethernet HWaddr 00:16:EC:AF:CB:CB inet addr:10.0.1.3 Bcast:10.255.255.255 Mask:255.255.255.0 inet6 addr: fe80::216:ecff:feaf:cbcb/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4564 errors:0 dropped:0 overruns:0 frame:0 TX packets:6688 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:459463 (448.6 KiB) TX bytes:546633 (533.8 KiB) Interrupt:23 Base address:0x6000
在①號(hào)機(jī)ping 的同時(shí)，我在④號(hào)機(jī)抓eth1包，結(jié)果如下：
[root@h4~]# tcpdump -i eth1 -enntcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes15:26:44.388614 00:16:ec:af:cb:cb > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.4.3 tell 10.0.1.3, length 4615:26:45.391014 00:16:ec:af:cb:cb > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.4.3 tell 10.0.1.3, length 4615:26:47.387821 00:16:ec:af:cb:cb > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.4.3 tell 10.0.1.3, length 4615:26:48.391220 00:16:ec:af:cb:cb > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.4.3 tell 10.0.1.3, length 4615:26:49.392621 00:16:ec:af:cb:cb > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.4.3 tell 10.0.1.3, length 46
可見(jiàn)①號(hào)一直在尋找配有10.0.4.3 IP的機(jī)子的mac地址，即一直在發(fā)arp包。但是路由器（④號(hào)機(jī)）默認(rèn)是不轉(zhuǎn)發(fā)arp報(bào)文的，所有①號(hào)機(jī)永遠(yuǎn)也ping不通⑦號(hào)機(jī)。
3、正確的配置
在①號(hào)機(jī)種配置路由，命令如下：
route add -net 10.0.4.0/24 gw 10.0.1.2
這時(shí)候①號(hào)機(jī)的路由表：
[root@h1 ~]# [root@h1 ~]# route -nKernel IP routing tableDestination Gateway Genmask Flags Metric Ref Use Iface10.0.4.0 10.0.1.2 255.255.255.0 UG 0 0 0 eth110.0.5.0 0.0.0.0 255.255.255.0 U 0 0 0 eth210.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1192.168.99.0 0.0.0.0 255.255.255.0 U 1 0 0 eth00.0.0.0 192.168.99.1 0.0.0.0 UG 0 0 0 eth0
同樣的方法配置⑦號(hào)機(jī)的路由表
root@h7:~# route -n內(nèi)核 IP 路由表目標(biāo) 網(wǎng)關(guān) 子網(wǎng)掩碼 標(biāo)志 躍點(diǎn) 引用 使用 接口0.0.0.0 192.168.99.1 0.0.0.0 UG 0 0 0 eth010.0.1.0 10.0.4.2 255.255.255.0 UG 0 0 0 eth110.0.4.0 0.0.0.0 255.255.255.0 U 1 0 0 eth110.0.7.0 0.0.0.0 255.255.255.0 U 1 0 0 eth2192.168.99.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
下面再進(jìn)行ping測(cè)試，在①號(hào)機(jī)ping⑦號(hào)機(jī)，結(jié)果能夠ping通。在這里我們問(wèn)了方便分析,首先列出各網(wǎng)卡的MAC地址
①號(hào)機(jī) eth1:HWaddr 00:16:EC:AF:CB:CB④號(hào)機(jī) eth1:HWaddr 40:61:86:32:8F:0B ④號(hào)機(jī) eth4:HWaddr 40:61:86:32:8F:0E⑦號(hào)機(jī) eth1:HWaddr 00:25:90:93:40:79
④號(hào)機(jī)eth1抓包如下：
[root@h4 ~]# tcpdump -i eth1 -enntcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes16:02:26.809445 00:16:ec:af:cb:cb > 40:61:86:32:8f:0b, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 1, length 6416:02:26.810723 40:61:86:32:8f:0b > 00:16:ec:af:cb:cb, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 1, length 6416:02:27.811847 00:16:ec:af:cb:cb > 40:61:86:32:8f:0b, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 2, length 6416:02:27.813136 40:61:86:32:8f:0b > 00:16:ec:af:cb:cb, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 2, length 6416:02:28.813248 00:16:ec:af:cb:cb > 40:61:86:32:8f:0b, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 3, length 6416:02:28.814551 40:61:86:32:8f:0b > 00:16:ec:af:cb:cb, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 3, length 6416:02:29.814648 00:16:ec:af:cb:cb > 40:61:86:32:8f:0b, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 4, length 64
④號(hào)機(jī)eth4抓包如下：
root@h4 ~]# tcpdump -i eth4 -enntcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth4, link-type EN10MB (Ethernet), capture size 65535 bytes16:02:26.809460 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 1, length 6416:02:26.810715 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 1, length 6416:02:27.811853 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 2, length 6416:02:27.813130 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 2, length 6416:02:28.813255 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 3, length 6416:02:28.814545 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 3, length 64
⑦號(hào)機(jī)eth1抓包如下：
root@h7:~# tcpdump -i eth1 -enntcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes16:02:27.222853 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 1, length 6416:02:27.222867 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 1, length 6416:02:28.225226 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 2, length 6416:02:28.225237 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 2, length 6416:02:29.226638 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 3, length 6416:02:29.226649 00:25:90:93:40:79 > 40:61:86:32:8f:0e, ethertype IPv4 (0x0800), length 98: 10.0.4.3 > 10.0.1.3: ICMP echo reply, id 8079, seq 3, length 6416:02:30.228059 40:61:86:32:8f:0e > 00:25:90:93:40:79, ethertype IPv4 (0x0800), length 98: 10.0.1.3 > 10.0.4.3: ICMP echo request, id 8079, seq 4, length 64
從抓取的包中我們不難看出，①號(hào)機(jī)在ping ⑦號(hào)機(jī)時(shí)，由于其中路由表配置了通過(guò)四號(hào)機(jī)的eth1（10.0.1.2）地址，這個(gè)地址對(duì)應(yīng)的mac①號(hào)機(jī)已經(jīng)緩存了，所有沒(méi)有進(jìn)行arp廣播就直接開(kāi) 始發(fā)送ICMP包，并且目的ip是⑦號(hào)機(jī)，目的MAC是④號(hào)機(jī)的eth1的，之后在④號(hào)機(jī)路由中又將目的MAC變成了④號(hào)機(jī)的eth4的，目的ip不變， 回來(lái)的過(guò)程相仿。
4、結(jié)論
由 于linux路由器默認(rèn)不轉(zhuǎn)發(fā)arp報(bào)文到,所有若像”錯(cuò)誤的配置“那樣配置路由，①號(hào)機(jī)一直處在詢問(wèn)目的MAC的階段而無(wú)法讓路由器④號(hào)機(jī)轉(zhuǎn)發(fā)數(shù)據(jù)包， 所有我們可以通過(guò)”正確的配置“那樣配置路由讓①號(hào)機(jī)使用④號(hào)機(jī)eth1的MAC出去，然后再一步一步轉(zhuǎn)發(fā)。或者通過(guò)”錯(cuò)誤的配置“那樣配置路由，然后在 ④號(hào)機(jī)中使用arp代理，從而讓①號(hào)機(jī)獲得⑦號(hào)機(jī)的MAC，從而從發(fā)送arp報(bào)文階段到發(fā)送ICMP包階段。謝謝閱讀，希望能幫到大家，請(qǐng)繼續(xù)關(guān)注腳本之家，我們會(huì)努力分享更多優(yōu)秀的文章。
