IGMP Snooping

man tcpdump | less -Ip examples, чтобы увидеть некоторые примеры

фильтр tcpdump для HTTP GET:

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

фильтр tcpdump для HTTP POST:

sudo tcpdump -s 0 -A 'tcp dst port 80 and (tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354)'

Мониторинг HTTP-трафика, включая заголовки запросов и ответов и тело сообщения (источник):

tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
tcpdump -X -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'

List interfaces that tcpdump can listen on

# tcpdump -D 1.eth0 2.eth1 3.eth1.780 4.eth1.781 5.eth1.790 6.eth2 7.eth2.10 8.eth3 9.eth4 10.any (Pseudo-device that captures on all interfaces) 11.lo

Note: “any” interface is an option only on Linux systems running kernel 2.4 onwards. Not available on *BSD, Solaris or any other Unix system.

Turn on "verbose" key in TCPDUMP to see IP and TCP header information

tcpdump -vi eth0

Turn off hostname and port lookup in TCPDUMP

tcpdump -vnni eth0

Tcpdump filter only icmp traffic

tcpdump -nni eth0 icmp

Tcpdump command to filter on ICMP type - capture only ICMP echo request

As shows on ICMP wiki page http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol, ICMP echo requests are ICMP type 8 ( ICMP code is not important as there is only one code for ICMP type 8 [ and 0 actually ] )

tcpdump -nni vlan111 -e icmp[icmptype] == 8 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vlan111, link-type EN10MB (Ethernet), capture size 65535 bytes 12:39:05.471531 00:07:e9:a5:9b:fa > 00:10:db:ff:10:02, ethertype IPv4 (0x0800), length 98: 10.1.111.10 > 10.0.0.4: ICMP echo request, id 24907, seq 307, length 64 12:39:06.472431 00:07:e9:a5:9b:fa > 00:10:db:ff:10:02, ethertype IPv4 (0x0800), length 98: 10.1.111.10 > 10.0.0.4: ICMP echo request, id 24907, seq 308, length 64

Above tcpdump filter “icmp[icmptype] == 8” will only display ip packets that have icmp payload and icmptype 8 - ICMP Echo Request.

Tcpdump command to filter on ICMP type - capture only ICMP echo reply

# tcpdump -nni vlan111 -e icmp[icmptype] == 0 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vlan111, link-type EN10MB (Ethernet), capture size 65535 bytes 12:40:52.569668 00:10:db:ff:10:02 > 00:07:e9:a5:9b:fa, ethertype IPv4 (0x0800), length 98: 10.0.0.4 > 10.1.111.10: ICMP echo reply, id 24907, seq 414, length 64 12:40:53.570530 00:10:db:ff:10:02 > 00:07:e9:a5:9b:fa, ethertype IPv4 (0x0800), length 98: 10.0.0.4 > 10.1.111.10: ICMP echo reply, id 24907, seq 415, length 64

Notice from ICMP types and codes table that icmptype 0 is the echo reply.

Tcpdump filter packets with specified ip identification in ip header

(See https://forum.ivorde.com/tcpdump-filter-packets-with-specified-ip-identification-in-ip-header-t19601.html for more details)

# tcpdump -nr /tmp/tcpdump.pcap -v 'ip[4:2] == 24332' reading from file /tmp/tcpdump.pcap, link-type EN10MB (Ethernet) capability mode sandbox enabled 23:58:50.090759 IP (tos 0x10, ttl 128, id 24332, offset 0, flags [DF], proto TCP (6), length 204) 10.1.1.1.22 > 192.168.0.109.53989: Flags [P.], seq 3661036793:3661036957, ack 2364476704, win 4106, length 164

Tcpdump filtering based on DSCP field in IP header

(See https://forum.ivorde.com/tcpdump-how-to-to-capture-only-ip-packets-with-specific-dscp-class-in-ip-header-t14041.html for more details)

# tcpdump -nni eth1 -v 'ip[1] & 0xfc == 184' 12:56:49.690239 IP (tos 0xb8, ttl 63, id 44823, offset 0, flags [DF], proto TCP (6), length 40) 28.32.179.11.80 > 61.219.73.106.61244: Flags [F.], cksum 0xdac1 (correct), seq 2799324281, ack 4189664666, win 108, length 0

Tcpdump: How to to capture only ICMP Fragmentation needed notifications

(See https://forum.ivorde.com/tcpdump-how-to-to-capture-only-icmp-fragmentation-needed-notifications-t15211.html)

# tcpdump -nni vlan111 -e icmp[icmptype] == 3 && icmp[icmpcode] == 4 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vlan111, link-type EN10MB (Ethernet), capture size 65535 bytes 12:46:41.500646 00:10:db:ff:10:02 > 00:07:e9:a5:9b:fa, ethertype IPv4 (0x0800), length 70: 10.1.111.1 > 10.1.111.10: ICMP 10.0.0.3 unreachable - need to frag (mtu 1382), length 36

How to capture frames with specific source or destination mac address

(See https://forum.ivorde.com/tcpdump-how-to-capture-frames-with-specific-source-destination-mac-address-t19471.html)

tcpdump -nni eth0 ether src 2c:21:72:c6:c1:88

tcpdump -nni eth0 ether dst 2c:21:72:c6:c1:88

Capture only packets from a specific IP host or to a specific IP destination

$ tcpdump -nni en0 src host 8.8.8.8.8

$ tcpdump -nni en0 dst host 8.8.8.8.8

Tcpdump - capture only ARP packets

$ tcpdump -nni en0 arp

Capture only IPv4 or only IPv6 traffic

$ tcpdump -nni en0 ip

$ tcpdump -nni en0 ip6

Capture ethernet multicast traffic based on ethernet field and on IPv4 destination

$ tcpdump -nni en0 "ether[0] & 1 != 0"

(Make sure the tcpdump expression above is enclosed in double quotes otherwise the &amp; will be interpreted by the shell not by tcpdump).

$ tcpdump -nni en0 dst net 224.0.0.0/4

Show ethernet / layer 2 headers

$ tcpdump -nni en0 -e 21:54:03.017194 80:71:1f:39:61:c8 > 80:e6:50:07:2d:d6, ethertype IPv4 (0x0800), length 126: 64.233.166.189.443 > 192.168.3.100.57904: Flags [P.], seq 2082387620:2082387680, ack 1352514330, win 1373, options [nop,nop,TS val 1373308623 ecr 829302794], length 60

Capture only specific vlan traffic (for interfaces that terminate vlan trunks)

# tcpdump -nni em2 -e vlan 5 20:55:32.265019 f8:c0:01:d2:35:c1 > 00:26:0b:28:5e:40, ethertype 802.1Q (0x8100), length 370: vlan 5, p 0, ethertype IPv4, 12.16.11.149 > 12.250.3.6: ESP(spi=0x0f3e6725,seq=0x72f), length 332

Capture specific IPv4 protocols related traffic

IPv4 protocols are defined in any Linux/*BSD under /etc/protocols so if your having a temporary lack of memory, it's place to match protocol names against their id.

# grep -E "esp|ah|gre|ospf|icmp|tcp|udp" /etc/protocols icmp 1 ICMP # internet control message protocol tcp 6 TCP # transmission control protocol udp 17 UDP # user datagram protocol gre 47 GRE # General Routing Encapsulation esp 50 IPSEC-ESP # Encap Security Payload [RFC2406] ah 51 IPSEC-AH # Authentication Header [RFC2402] ipv6-icmp 58 IPv6-ICMP # ICMP for IPv6 ospf 89 OSPFIGP # Open Shortest Path First IGP udplite 136 UDPLite # UDP-Lite [RFC3828] wesp 141 WESP # Wrapped Encapsulating Security Payload

Showing below how to capture GRE traffic.

# tcpdump -nni em2 ip proto 47 tcpdump: WARNING: em2: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on em2, link-type EN10MB (Ethernet), capture size 65535 bytes 21:17:32.870695 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto GRE (47), length 100) 12.16.81.123 > 82.210.283.106: GREv0, Flags [none], length 80 IP6 (class 0xc0, hlim 1, next-header OSPF (89) payload length: 36) fe80::fac0:100:d2:3580 > ff02::5: OSPFv3, Hello, length 36 Router-ID 172.16.2.2, Backbone Area Options [V6, External, Router] Hello Timer 10s, Dead Timer 40s, Interface-ID 0.0.0.2, Priority 128 Neighbor List:

Dump HTTP data as ASCII or ASCII and HEX

(See https://forum.ivorde.com/tcpdump-dump-http-headers-as-ascii-and-hex-t19591.html for more details)

# tcpdump -nni eth0 -s0 -A -l port 80

# tcpdump -nni eth0 -s0 -AX -l port 80

The output can be filtered with grep to only dump specific attribute in HTTP header or specific html tag inside the payload.

Capture only traffic related to a CIDR subnet

# tcpdump -nni eth0 net 192.168.3.96/28 02:48:33.958798 IP 10.1.22.2.22 > 192.168.3.100.61644: Flags [P.], seq 2001101694:2001101886, ack 4183269133, win 49, options [nop,nop,TS val 1422334877 ecr 843342387], length 192 02:48:33.962744 IP 10.1.22.2.22 > 192.168.3.100.61644: Flags [P.], seq 192:416, ack 1, win 49, options [nop,nop,TS val 1422334878 ecr 843342387], length 224