Run time configurable parameters

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The kernel allows you to change many parameters at run time. If you take a careful look at the /proc/sys/net/ directory structure you will see many files with useful names that describe various parameters for the network configuration. The files in the /proc/sys/net/ax25/ directory each represent one configured AX.25 port. The name of the file relates to the name of the port.

The structure of the files in /proc/sys/net/ax25/portname/ is as follows:

Filename Meaning Values Default
ip_default_mode IP Default Mode 0=DG 1=VC 0
ax25_default_mode AX.25 Default Mode 0=Normal 1=Extended 0
backoff_type Backoff 0=Linear 1=Exponential 1
connect_mode Connected Mode 0=No 1=Yes 1
standard_window_size Standard Window 1 .. 7 2
extended_window_size Extended Window 1 .. 63 32
t1_timeout T1 Timeout 1s .. 30s 10s
t2_timeout T2 Timeout 1s .. 20s 3s
t3_timeout T3 Timeout 0s .. 3600s 300s
idle_timeout Idle Timeout 0m or greater 20m
maximum_retry_count N2 1 .. 31 10
maximum_packet_length AX.25 Frame Length 1 .. 512 256

In the table T1, T2 and T3 are given in seconds, and the Idle Timeout is given in minutes. But please note that the values used in the sysctl interface are given in internal units where the time in seconds is multiplied by 10, this allows resolution down to 1/10 of a second. With timers that are allowed to be zero, e.g. T3 and Idle, a zero value indicates that the timer is disabled.

The structure of the files in /proc/sys/net/netrom/ is as follows:

Filename Meaning Values Default
default_path_quality 10
link_fails_count 2
network_ttl_initialiser 16
obsolescence_count_initialiser 6
routing_control 1
transport_acknowledge_delay 50
transport_busy_delay 1800
transport_maximum_tries 3
transport_requested_window_size 4
transport_timeout 1200

The structure of the files in /proc/sys/net/rose/ is as follows:

Filename Meaning Values Default
acknowledge_hold_back_timeout 50
call_request_timeout 2000
clear_request_timeout 1800
link_fail_timeout 1200
maximum_virtual_circuits 50
reset_request_timeout 1800
restart_request_timeout 1800
routing_control 1
window_size 3

To set a parameter all you need to do is write the desired value to the file itself, for example to check and set the ROSE window size you'd use something like:

# cat /proc/sys/net/rose/window_size
# echo 4 >/proc/sys/net/rose/window_size
# cat /proc/sys/net/rose/window_size