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TCPdump & Wireshark tips & tricks - Different how-tos and some information I find interesting about the two most famous traffic analysis tools.

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 Post subject: tshark: CLI command to read ip/tcp headers
PostPosted: Wed May 25, 2016 11:07 am 
Code:
tshark -o tcp.relative_sequence_numbers:FALSE -V -r nat66-take2.pcap | less





"tshark" is a wireshark cli utility available on multiple systems. This example is taken from a Mac cli terminal.
tshark -o tcp.relative_sequence_numbers:FALSE -V -r nat66-take2.pcap | less
Frame 1: 94 bytes on wire (752 bits), 94 bytes captured (752 bits)
Encapsulation type: Ethernet (1)
Arrival Time: May 17, 2016 13:45:23.955177000 CEST
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1463485523.955177000 seconds
[Time delta from previous captured ...

Read more : tshark: CLI command to read ip/tcp headers | Views : 1568 | Replies : 0

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 Post subject: tcpdump -xx -XX - dump packet header and data in hex and ASCII format
PostPosted: Thu Mar 19, 2015 5:33 am 
To troubleshoot network protocols or network filters (firewalls and Intrussion Detection Systems) sometimes it is required to look at the packets hex dump either live or at a packet capture taken while the investigated issue was happening. tcpdump -xx can be used to print packet hex data and layer 2 header information (when debugging ethernet mac address).

Quote:
-x When parsing and printing, in addition to printing the headers of each packet, print the data ...

Read more : tcpdump -xx -XX - dump packet header and data in hex and ASCII format | Views : 20483 | Replies : 0

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 Post subject: Tcpdump filter packets with specified ip identification in ip header
PostPosted: Wed Jan 14, 2015 5:15 am 
This article explains how to use tcpdump on a libcap formatted capture file to filter a specific ip id (not that I would like to go into how can a packet ID be predicted on an interface :) ).
Many network security engineers ave to deal with situations when a firewall, IPS system, proxy or even a router/switch drops a specific file (reasons are unnumbered) and when ...

Read more : Tcpdump filter packets with specified ip identification in ip header | Views : 6056 | Replies : 0

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 Post subject: Tcpdump - dump HTTP headers as ASCII and HEX
PostPosted: Wed Jan 14, 2015 5:13 am 
The internet is a mix of protocols or suite of protocols at multiple OSI layers that carry information from one host to the another (or others). Some of these protocols are encrypted before being sent out and others are sent in clear text - anyone with access to the wire can parse and read them in clear text. Some of these are the very well known HTTP, FTP, DNS and SMTP (web, file transfer, domain ...

Read more : Tcpdump - dump HTTP headers as ASCII and HEX | Views : 37329 | Replies : 2

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 Post subject: Tcpdump icmp practical examples filtering on icmp type field and icmp code field
PostPosted: Wed Jan 14, 2015 5:00 am 
The manual for tcpdump shows how to use tcpdump expressions and primitives to build traffic capturing filters based on protocol field values, like specific icmp type and specific icmp code and specific source host.

Tcpdump also offers a way to filter packets with specified value in a specific protocol byte number, ie: we know icmp header first byte (0) is icmp type and second byte (1) is the icmp code so tcpdump allows to either ...

Read more : Tcpdump icmp practical examples filtering on icmp type field and icmp code field | Views : 9342 | Replies : 0

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 Post subject: tcpdump: How to capture frames with specific source destination mac address
PostPosted: Mon Jan 12, 2015 10:36 am 
tcpdump: How to capture frames with specific source destination mac address

Tcpdump is a tool we all use and love, we use it in our daily life and, contrary to it's name, it can filter based on layer 2, layer 3 and layer4 headers. It can filter on protocols other than tcp.


Below is how tcpdump filters frames based on their source ethernet (mac) address:
Code:
tcpdump -nni eth0 ether src 2c:21:72:c6:c1:88


Below is ...

Read more : tcpdump: How to capture frames with specific source destination mac address | Views : 27030 | Replies : 0

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 Post subject: Tcpdump: How to to capture only ICMP Fragmentation needed notifications
PostPosted: Thu Aug 22, 2013 6:50 am 
How to capture only ICMP Destination unreachable - Fragmentation required and DF bit set in tcpdump.

Man tcpdump quote:
Quote:
Quote:
Some offsets and field values may be expressed as names
rather than as numeric values. The following protocol
header field offsets are available: icmptype (ICMP type
field), icmpcode (ICMP code field), and tcpflags (TCP
flags field).



As shows on ICMP wiki page http://en.wikipedia.org/wiki/Internet_C ... e_Protocol, ICMP Destination unreachable is ...

Read more : Tcpdump: How to to capture only ICMP Fragmentation needed notifications | Views : 8352 | Replies : 0

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 Post subject: Tcpdump: How to to capture only ICMP (ping) echo replies
PostPosted: Thu Aug 22, 2013 6:41 am 
How to capture only ping echo replies with tcpdump.

Man tcpdump quote:
Quote:
Some offsets and field values may be expressed as names
rather than as numeric values. The following protocol
header field offsets are available: icmptype (ICMP type
field), icmpcode (ICMP code field), and tcpflags (TCP
flags field).


As shows on ICMP wiki page http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol, ICMP echo replies are ICMP type 0 ( ICMP code is not important as there is only one ...

Read more : Tcpdump: How to to capture only ICMP (ping) echo replies | Views : 196 | Replies : 0

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 Post subject: Tcpdump: How to to capture only ICMP (ping) echo requests
PostPosted: Thu Aug 22, 2013 6:39 am 
How to capture only ping echo requests with tcpdump.
More detail article: Tcpdump icmp practical examples filtering on icmp type field and icmp code field.
Man tcpdump quote:
Quote:
Some offsets and field values may be expressed as names
rather than as numeric values. The following protocol
header field offsets are available: icmptype (ICMP type
field), icmpcode (ICMP code field), and tcpflags (TCP
flags field).


List interfaces that tcpdump can listen on



# ...

Read more : Tcpdump: How to to capture only ICMP (ping) echo requests | Views : 279383 | Replies : 0

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 Post subject: Tcpdump: How to to capture only IP packets with specific DSCP class in IP header
PostPosted: Wed Apr 10, 2013 8:59 am 
Tcpdump filtering based on DSCP field in IP header.

DSCP stands for "DIfferentiated Services Code Point" and it refers to second byte in IP header (TOS - Type Of Service ip), specifically to first 6 bits in this byte (last 2 are ECN).

By looking at the DSCP code point table (http://www.juniper.net/techpubs/software/junos-security/junos-security10.2/junos-security-swconfig-class-of-service/default-cos-section.html), let's say we want to capture only those packets with "ef" (expedited forwarding) forwarding class.


Quote:
ef 101110



So the first 6 bits ...

Read more : Tcpdump: How to to capture only IP packets with specific DSCP class in IP header | Views : 13151 | Replies : 0

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