Section: User Commands (1)
Updated: 16 May 2003
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nemesis-tcp - TCP Protocol (The Nemesis Project)  


nemesis-tcp [-vZ?] [-a ack-number ] [-d Ethernet-device ] [-D destination-IP-address ] [-f TCP-flags ] [-F fragmentation-options ] [-I IP-ID ] [-M destination-MAC-address ] [-o TCP-options-file ] [-O IP-options-file ] [-P payload-file ] [-s sequence-number ] [-S source-IP-address ] [-t IP-TOS ] [-T IP-TTL ] [-u urgent-pointer ] [-w window-size ] [-x source-port ] [-y destination-port ]  


The Nemesis Project is designed to be a command line-based, portable human IP stack for UNIX-like and Windows systems. The suite is broken down by protocol, and should allow for useful scripting of injected packets from simple shell scripts.

nemesis-tcp provides an interface to craft and inject TCP packets allowing the user to specify any portion of a TCP packet as well as lower-level IP packet information.  

TCP Options

-a Acknowledgement-Number
Specify the acknowledgement-number (ACK number) within the TCP header.
-f TCP flags (-fS/-fA/-fR/-fP/-fF/-fU/-fE/-fC/-f-)
Specify the TCP flags:

-fS (SYN)
-fA (ACK)
-fR (RST)
-fP (PSH)
-fF (FIN)
-fU (URG)
-fE (ECE)
-fC (CWR)
-f- NONE

within the TCP header. Flags can be combined in the form '-fPA'. If flags are specified in the form '-f-' then the TCP header will be built without flags.

-o TCP-options-file
This will cause nemesis-dns to use the specified TCP-options-file as the options when building the TCP header for the injected packet. TCP options can be up to 40 bytes in length. The TCP options file must be created manually based upon the desired options. TCP options can also be read from stdin by specifying '-o -' instead of a TCP-options-file.
-P payload-file
This will case nemesis-tcp to use the specified payload-file as the payload when injecting TCP packets. For packets injected using the raw interface (where -d is not used), the maximum payload size is 65415 bytes. For packets injected using the link layer interface (where -d IS used), the maximum payload size is 1380 bytes. Payloads can also be read from stdin by specifying '-P -' instead of a payload file.

Windows systems are limited to a maximum payload size of 1380 bytes for TCP packets.

-s sequence-number
Specify the sequence-number within the TCP header.
-u urgent-pointer-offset
Specify the urgent-pointer-offset within the TCP header.
-v verbose-mode
Display the injected packet in human readable form. Use twice to see a hexdump of the injected packet with printable ASCII characters on the right. Use three times for a hexdump without decided ASCII.
-w window-size
Specify the window-size within the TCP header.
-x source-port
Specify the source-port packet within the TCP header.
-y destination port
Specify the destintion-port within the TCP header.


-D destination-IP-address
Specify the destination-IP-address within the IP header.
-F fragmentation-options (-F[D],[M],[R],[offset])
Specify the fragmentation options:

-FD (don't fragment)
-FM (more fragments)
-FR (reserved flag)
-F <offset>

within the IP header. IP fragmentation options can be specified individually or combined into a single argument to the -F command line switch by separating the options with commas (eg. '-FD,M') or spaces (eg. '-FM 223'). The IP fragmentation offset is a 13-bit field with valid values from 0 to 8189. Don't fragment (DF), more fragments (MF) and the reserved flag (RESERVED or RB) are 1-bit fields.

NOTE: Under normal conditions, the reserved flag is unset.

Specify the IP-ID within the IP header.
-O IP-options-file
This will cause nemesis-tcp to use the specified IP-options-file as the options when building the IP header for the injected packet. IP options can be up to 40 bytes in length. The IP options file must be created manually based upon the desired options. IP options can also be read from stdin by specifying '-O -' instead of an IP-options-file.
-S source-IP-address
Specify the source-IP-address within the IP header.
Specify the IP-type-of-service (TOS) within the IP header. Valid type of service values:

2  (Minimize monetary cost)
4  (Maximize reliability)
8  (Maximize throughput)
24 (Minimize delay)

NOTE: Under normal conditions, only one type of service is set within a packet. To specify multiple types, specify the sum of the desired values as the type of service.

Specify the IP-time-to-live (TTL) within the IP header.


-d Ethernet-device
Specify the name (for UNIX-like systems) or the number (for Windows systems) of the Ethernet-device to use (eg. fxp0, eth0, hem0, 1).
-H source-MAC-address
Specify the source-MAC-address (XX:XX:XX:XX:XX:XX).
-M destination-MAC-address
Specify the defination-MAC-address (XX:XX:XX:XX:XX:XX).
-Z list-network-interfaces
Lists the available network interfaces by number for use in link-layer injection.

NOTE: This feature is only relevant to Windows systems.



Nemesis-tcp returns 0 on a successful exit, 1 if it exits on an error.  


Send concise and clearly written bug reports to  


Jeff Nathan <>

Originally developed by Mark Grimes <>  


nemesis-arp(1), nemesis-dns(1), nemesis-ethernet(1), nemesis-icmp(1), nemesis-igmp(1), nemesis-ip(1), nemesis-ospf(1), nemesis-rip(1), nemesis-udp(1)



TCP Options

This document was created by man2html and sed, using the manual pages.
Time: 08:54:05 GMT, November 04, 2003