FORCE_BIND(1)

NAME
FORCE_BIND

AUTHOR
Catali(ux) M. BOIE - catab at embedromix dot ro

DESCRIPTION
Force an application to bind on a specific IP and/or port. Works with both IPv4 and IPv6. It is useful if you have a binary application without sources and without the possibility to configure address or port to bind to.

LICENSE
GPLv3

HOW IT WORKS
force_bind is a shared object that is loaded with LD_PRELOAD and hooks 'bind' function. Forcing an IP/port to bind to is done with environments variables.

EXAMPLES
0. Output debug stuff in a log file (for debugging):

export FORCE_NET_VERBOSE=999

export FORCE_NET_LOG="xxx.log"

your_program_here

1. Force bind to 127.0.0.1, port 33, verbose operations:

export FORCE_NET_VERBOSE=1

export FORCE_BIND_ADDRESS_V4=127.0.0.1

export FORCE_BIND_PORT_V4=33

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

2. Force binding to 127.0.0.2, port unchanged

export FORCE_BIND_ADDRESS_V4=127.0.0.2

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

3. Force binding to ::1 (IPv6), port unchanged

export FORCE_BIND_ADDRESS_V6=::1

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

4. Changing TOS on all sockets to 30

export FORCE_NET_TOS=30

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

5. Force Keep alive to 60 seconds:

export FORCE_NET_KA=60

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

6. Force MSS to 1400

export FORCE_NET_MSS=1400

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

7. Force bandwidth to 1000 bytes/s for _all_ connections, cumulated

export FORCE_NET_BW=1000

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

8. Force bandwidth to 20000 bytes/s per socket

export FORCE_NET_BW_PER_SOCKET=20000

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

9. Force REUSEADDR

export FORCE_NET_REUSEADDR=1

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

10. Force NODELAY

export FORCE_NET_NODELAY=1

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

11. Force client connections (for example 'telnet', 'ssh', 'firefox') to connect from a specified address, not the auto selected one:

export FORCE_NET_VERBOSE=1

export FORCE_BIND_ADDRESS_V4=127.0.0.2

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

12. Set a FLOWINFO (flow label + class) for a client connection:

export FORCE_NET_VERBOSE=1

export FORCE_NET_FLOWINFO=0x7812345 # class 0x78, label 0x12345

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

13. Force FWMARK on a connection (only root is allowed):

export FORCE_NET_VERBOSE=1

export FORCE_NET_FWMARK=0x1234

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

14. Force priority (between 0 and 6 for non-root users). You can use 'tc' command from iproute to set-up 'prio' qdisc and to assign prio to queues:

# 0. setup

export FORCE_NET_VERBOSE=1

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

# 1. Make sure you have a 'prio' qdisc attached to eth0, for example:

tc qdisc add ev eth0 root handle 1: prio

# 2. Assign applications to classed (bands):

export FORCE_NET_PRIO=6 # interactive, band 0

your_voip_program_here

export FORCE_NET_PRIO=0 # best effort, band 1

your_mail_program_here

export FORCE_NET_PRIO=2 # bulk, band 2

your_remote_backup_program_here

# 3. Run tc statistics so you can see the classification:

tc -s class show dev eth0

15. Deny binding to any IPv4 sockets. The bind syscall will return -1 and errno will be set to EACCES.

export FORCE_NET_VERBOSE=1

export FORCE_BIND_ADDRESS_V4=deny

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here

16. Silent fake binding to any IPv6 sockets. The bind will return success, but will never accept any connection.

export FORCE_NET_VERBOSE=1

export FORCE_BIND_ADDRESS_V6=fake

export LD_PRELOAD=${LD_PRELOAD}:/usr/lib/force_bind.so

your_program_here