在网络问题的调试中，tcpdump应该说是一个必不可少的工具，和大部分linux下优秀工具一样，它的特点就是简单而强大。它是基于Unix系统的命令行式的数据包嗅探工具，可以抓取流动在网卡上的数据包。

图片

监听所有网卡所有包

tcpdump

监听指定网卡的包

tcpdump -i ens18

监听指定IP的包

tcpdump host 192.168.1.11

监听指定来源IP

tcpdump src host 192.168.1.11

监听目标地址IP

tcpdump dst host 192.168.1.11

监听指定端口

tcpdump port 80

监听TCP

tcpdump tcp

监听UDP

tcpdump udp

监听192.168.1.11的tcp协议的80端口的数据包

tcpdump tcp port 80 and src host 192.168.1.11

11:59:07.836563 IP 192.168.1.11.39680 > hello.http: Flags [.], ack 867022485, win 502, length 0
11:59:07.836711 IP 192.168.1.11.39680 > hello.http: Flags [P.], seq 0:77, ack 1, win 502, length 77: HTTP: HEAD / HTTP/1.1
11:59:07.838462 IP 192.168.1.11.39680 > hello.http: Flags [.], ack 248, win 501, length 0
11:59:07.838848 IP 192.168.1.11.39680 > hello.http: Flags [F.], seq 77, ack 248, win 501, length 0
11:59:07.839192 IP 192.168.1.11.39680 > hello.http: Flags [.], ack 249, win 501, length 0

监听IP之间的包

tcpdump ip host 192.168.1.11 and 192.168.1.60

11:57:52.742468 IP 192.168.1.11.38978 > hello.http: Flags [S], seq 3437424457, win 64240, options [mss 1460,sackOK,TS val 2166810854 ecr 0,nop,wscale 7], length 0
11:57:52.742606 IP hello.http > 192.168.1.11.38978: Flags [S.], seq 3541873211, ack 3437424458, win 64240, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0
11:57:52.742841 IP 192.168.1.11.38978 > hello.http: Flags [.], ack 1, win 502, length 0
11:57:52.742927 IP 192.168.1.11.38978 > hello.http: Flags [P.], seq 1:78, ack 1, win 502, length 77: HTTP: HEAD / HTTP/1.1
11:57:52.742943 IP hello.http > 192.168.1.11.38978: Flags [.], ack 78, win 502, length 0
11:57:52.744407 IP hello.http > 192.168.1.11.38978: Flags [P.], seq 1:248, ack 78, win 502, length 247: HTTP: HTTP/1.1 200 OK
11:57:52.744613 IP 192.168.1.11.38978 > hello.http: Flags [.], ack 248, win 501, length 0
11:57:52.744845 IP 192.168.1.11.38978 > hello.http: Flags [F.], seq 78, ack 248, win 501, length 0
11:57:52.745614 IP hello.http > 192.168.1.11.38978: Flags [F.], seq 248, ack 79, win 502, length 0
11:57:52.745772 IP 192.168.1.11.38978 > hello.http: Flags [.], ack 249, win 501, length 0

监听除了与192.168.1.4之外的数据包

tcpdump ip host 192.168.1.60 and ! 192.168.1.4

11:57:20.862575 IP 192.168.1.9.47190 > hello.9200: Flags [P.], seq 3233461117:3233461356, ack 1301434191, win 9399, length 239
11:57:20.878165 IP hello.9200 > 192.168.1.9.47190: Flags [P.], seq 1:4097, ack 239, win 3081, length 4096
11:57:20.878340 IP hello.9200 > 192.168.1.9.47190: Flags [P.], seq 4097:8193, ack 239, win 3081, length 4096
11:57:20.878417 IP 192.168.1.9.47190 > hello.9200: Flags [.], ack 4097, win 9384, length 0

组合示例

tcpdump tcp -i ens18 -v -nn -t -A -s 0 -c 50 and dst port ! 22 and src net 192.168.1.0/24 -w ./cby.cap

(1)tcp: ip icmp arp rarp 和 tcp、udp、icmp这些选项等都要放到第一个参数的位置，用来过滤数据报的类型
(2)-i eth1 : 只抓经过接口eth1的包
(3)-t : 不显示时间戳
(4)-s 0 : 抓取数据包时默认抓取长度为68字节。加上-S 0 后可以抓到完整的数据包
(5)-c 50 : 只抓取50个数据包
(6)dst port ! 22 : 不抓取目标端口是22的数据包
(7)src net 192.168.1.0/24 : 数据包的源网络地址为192.168.1.0/24
(8)-w ./cby.cap : 保存成cap文件，方便用ethereal(即wireshark)分析
(9)-v 使用 -v，-vv 和 -vvv 来显示更多的详细信息，通常会显示更多与特定协议相关的信息。
(10)-nn 单个 n 表示不解析域名，直接显示 IP；两个 n 表示不解析域名和端口。
(11)-A 表示使用 ASCII 字符串打印报文的全部数据

组合过滤器  《与/AND/&&》 《或/OR/||》 《非/not/!》
and or &&
or or ||
not or !

在HTTP中提取用户头

tcpdump -nn -A -s0 -l | grep "User-Agent:"

User-Agent: Prometheus/2.30.0
User-Agent: Microsoft-Delivery-Optimization/10.0

在HTTP中同时提取用户头和主机信息

tcpdump -nn -A -s0 -l | egrep -i 'User-Agent:|Host:'

Host: 192.168.1.42:9200
User-Agent: Prometheus/2.30.0
HOST: 239.255.255.250:1900
USER-AGENT: Microsoft Edge/97.0.1072.55 Windows

抓取 HTTP GET 流量

tcpdump -s 0 -A -vv 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420'

11:55:13.704801 IP (tos 0x0, ttl 64, id 14605, offset 0, flags [DF], proto TCP (6), length 291)
    localhost.35498 > localhost.9200: Flags [P.], cksum 0x849a (incorrect -> 0xd0b0), seq 3090925559:3090925798, ack 809492640, win 630, options [nop,nop,TS val 2076158003 ecr 842090965], length 239
E..#9.@.@.}C... ...+..#..;..0?.....v.......
{..321I.GET /metrics HTTP/1.1
Host: 192.168.1.43:9200
User-Agent: Prometheus/2.30.0
Accept: application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1
Accept-Encoding: gzip
X-Prometheus-Scrape-Timeout-Seconds: 10

抓取 HTTP POST 请求流量

tcpdump -s 0 -A -vv 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354'

11:53:10.831855 IP (tos 0x0, ttl 63, id 0, offset 0, flags [none], proto TCP (6), length 643)
    localhost.47702 > dns50.online.tj.cn.http-alt: Flags [P.], cksum 0x1a41 (correct), seq 3331055769:3331056372, ack 799860501, win 4096, length 603: HTTP, length: 603
        POST /?tk=391f8956e632962ee9c1dc661a9b46779d86ca43fe252bddbfc09d2cc66bf875323f6e7f03b881db21133b1bf2ae5bc5 HTTP/1.1
        Host: 220.194.116.50:8080
        Accept: */*
        Accept-Language: zh-CN,zh-Hans;q=0.9
        Q-Guid: e54764008893a559b852b6e9f1c8ae268958471308f41a96fd42e477e26323b8
        Q-UA: 
        Accept-Encoding: gzip,deflate
        Q-UA2: QV=3&PL=IOS&RF=SDK&PR=IBS&PP=com.tencent.mqq&PPVN=3.8.0.1824&TBSVC=18500&DE=PHONE&VE=GA&CO=IMTT&RL=1170*2532&MO=iPhone14,2&CHID=50001&LCID=9751&OS=15.1.1
        Content-Length: 144
        User-Agent: 
        QQ-S-ZIP: gzip
        Connection: keep-alive
        Content-Type: application/multipart-formdata
        Q-Auth: 

E.......?.f.......t2.V....../...P....A..POST /?tk=391f8956e632962ee9c1dc661a9b46779d86ca43fe252bddbfc09d2cc66bf875323f6e7f03b881db21133b1bf2ae5bc5 HTTP/1.1
Host: 220.194.116.50:8080
Accept: */*
Accept-Language: zh-CN,zh-Hans;q=0.9
Q-Guid: e54764008893a559b852b6e9f1c8ae268958471308f41a96fd42e477e26323b8
Q-UA: 
Accept-Encoding: gzip,deflate
Q-UA2: QV=3&PL=IOS&RF=SDK&PR=IBS&PP=com.tencent.mqq&PPVN=3.8.0.1824&TBSVC=18500&DE=PHONE&VE=GA&CO=IMTT&RL=1170*2532&MO=iPhone14,2&CHID=50001&LCID=9751&OS=15.1.1
Content-Length: 144
User-Agent: 
QQ-S-ZIP: gzip
Connection: keep-alive
Content-Type: application/multipart-formdata
Q-Auth:

注意：一个 POST 请求会被分割为多个 TCP 数据包

提取 HTTP 请求的主机名和路径

root@pve:~# tcpdump -s 0 -v -n -l | egrep -i "POST /|GET /|Host:"

tcpdump: listening on eno1, link-type EN10MB (Ethernet), snapshot length 262144 bytes
        GET /gchatpic_new/2779153238/851197814-3116860870-F4902AF1432FE48B812982F082A31097/0?term=255&pictype=0 HTTP/1.1
        Host: 112.80.128.33
        GET /gchatpic_new/2779153238/851197814-3116860870-F4902AF1432FE48B812982F082A31097/0?term=255&pictype=0 HTTP/1.1
        Host: 112.80.128.33
        POST /mmtls/74ce36ed HTTP/1.1
        Host: extshort.weixin.qq.com
        POST /mmtls/74ce36ed HTTP/1.1
        Host: extshort.weixin.qq.com

从 HTTP 请求中提取密码和主机名

tcpdump -s 0 -v -n -l | egrep -i "POST /|GET /|pwd=|passwd=|password=|Host:"

        POST /index.php/action/login?_=b395d487431320461e9a6741e3828918 HTTP/1.1
        Host: x.oiox.cn
        name=cby&password=Cby****&referer=http%3A%2F%2Fx.oiox.cn%2Fadmin%2Fwelcome.php [|http]
        POST /index.php/action/login?_=b395d487431320461e9a6741e3828918 HTTP/1.1
        Host: x.oiox.cn
        name=cby&password=Cby****&referer=http%3A%2F%2Fx.oiox.cn%2Fadmin%2Fwelcome.php [|http]
        GET /admin/welcome.php HTTP/1.1
        Host: x.oiox.cn

从 HTTP 请求中提取Cookie信息

tcpdump -nn -A -s0 -l -v | egrep -i 'Set-Cookie|Host:|Cookie:'

Host: x.oiox.cn
Cookie: 8bf110c223e1a04b7b63ca5aa97c9f61__typecho_uid=1; 8bf110cxxxxxxxb7b63ca5aa97c9f61__typecho_authCode=%24T%24W3hV7B9vRfefa6593049ba02c33b3c4796a7cfa35; PHPSESSID=bq67s1n0cb9ml6dq254qpdvfec

通过排除 echo 和 reply 类型的数据包使抓取到的数据包不包括标准的 ping 包

tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'

11:20:32.285428 IP localhost > localhost: ICMP localhost udp port 64594 unreachable, length 36
11:20:32.522061 IP localhost > localhost: ICMP localhost udp port 58617 unreachable, length 36
11:20:37.736249 IP localhost > localhost: ICMP redirect 204.79.197.219 to host localhost, length 48
11:20:44.379646 IP localhost > 111.206.187.34: ICMP localhost udp port 37643 unreachable, length 36
11:20:44.379778 IP localhost > 111.206.187.34: ICMP localhost udp port 37643 unreachable, length 36
11:20:46.351245 IP localhost > localhost: ICMP redirect lt-in-f188.1e100.net to host localhost, length 49

可以通过过滤器 ip6 来抓取 IPv6 流量，同时可以指定协议如 TCP

root@vm371841:~# tcpdump -nn ip6 proto 6 -v

tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
06:40:26.060313 IP6 (flowlabel 0xfe65e, hlim 64, next-header TCP (6) payload length: 40) 2a00:b700::e831:2aff:fe27:e9d9.44428 > 2001:2030:21:181::26e7.443: Flags [S], cksum 0x451c (incorrect -> 0x24cd), seq 3503520271, win 64800, options [mss 1440,sackOK,TS val 2504544710 ecr 0,nop,wscale 6], length 0
06:40:34.296847 IP6 (flowlabel 0xc9f9c, hlim 64, next-header TCP (6) payload length: 40) 2a00:b700::e831:2aff:fe27:e9d9.55082 > 2a00:1450:4010:c0e::84.443: Flags [S], cksum 0x6754 (incorrect -> 0x0813), seq 3899361154, win 64800, options [mss 1440,sackOK,TS val 2141524802 ecr 0,nop,wscale 6], length 0

发起的出站 DNS 请求和 A 记录响应

tcpdump -i eth0 -s0 port 53

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
06:44:10.499529 IP vm371841.37357 > dns.yandex.ru.domain: 34151+ [1au] A? czr12g1e.slt-dk.sched.tdnsv8.com. (61)
06:44:10.500992 IP vm371841.56195 > dns.yandex.ru.domain: 45667+ [1au] PTR? 219.3.144.45.in-addr.arpa. (54)
06:44:10.661142 IP dns.yandex.ru.domain > vm371841.56195: 45667 NXDomain 0/1/1 (112)
06:44:10.661438 IP vm371841.56195 > dns.yandex.ru.domain: 45667+ PTR? 219.3.144.45.in-addr.arpa. (43)
06:44:10.687147 IP dns.yandex.ru.domain > vm371841.56195: 45667 NXDomain 0/1/0 (101)
06:44:10.806349 IP dns.yandex.ru.domain > vm371841.37357: 34151 11/0/1 A 139.170.156.155, A 220.200.129.141, A 58.243.200.63, A 113.59.43.25, A 124.152.41.39, A 139.170.156.154, A 59.83.204.154, A 123.157.255.158, A 113.200.17.157, A 43.242.166.42, A 116.177.248.23 (237)

抓取 DHCP 服务的请求和响应报文

tcpdump -v -n port 67 or 68

11:50:28.939726 IP (tos 0x0, ttl 64, id 35862, offset 0, flags [DF], proto UDP (17), length 320)
    192.168.1.136.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 70:3a:a6:cb:27:3c, length 292, xid 0x3ccba40c, secs 11529, Flags [none]
          Client-IP 192.168.1.136
          Client-Ethernet-Address 70:3a:a6:cb:27:3c
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Request
            Client-ID (61), length 7: ether 70:3a:a6:cb:27:3c
            Hostname (12), length 11: "S24G-U_273C"
            Vendor-Class (60), length 13: "CloudSwitch_1"
            MSZ (57), length 2: 800
            Parameter-Request (55), length 5: 
              Subnet-Mask (1), Default-Gateway (3), Hostname (12), Domain-Name-Server (6)
              Vendor-Class (60)

https://www.oiox.cn/

https://www.chenby.cn/

https://cby-chen.github.io/

https://weibo.com/u/5982474121

https://blog.csdn.net/qq_33921750

https://my.oschina.net/u/3981543

https://www.zhihu.com/people/chen-bu-yun-2

https://segmentfault.com/u/hppyvyv6/articles

https://juejin.cn/user/3315782802482007

https://space.bilibili.com/352476552/article

https://cloud.tencent.com/developer/column/93230

https://www.jianshu.com/u/0f894314ae2c

https://www.toutiao.com/c/user/token/MS4wLjABAAAAeqOrhjsoRZSj7iBJbjLJyMwYT5D0mLOgCoo4pEmpr4A/

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