#!/bin/tcsh -f

# /etc/network/tweaks
#
# Tweaks and optimizations to improve routing performance.  None of
# these settings should ever be required, but are tweaked here for
# performance improvements.  DO NOT PUT REQUIRED SETTINGS IN HERE,
# put them in /etc/network/interfaces or /etc/network/firewall.
#
# These are mostly undocumented, but some information can be found
# on the web.  Simon Kirby, 2002/09/17

#------------------------------------------------------------------------------

# Neighbour/ARP tweaks

cd /proc/sys/net/ipv4/neigh

# Raise the base reachable time (average ARP refresh time) to compensate for
# lowering the check intervals (later).

foreach a (*/)
	echo 42 > "$a"/base_reachable_time	# ARP/neigh refresh avg interval [dfl: 30]
	echo 300 > "$a"/gc_stale_time		# Check interval for stale neigh entries [dfl: 60]
end

# BLURP: I think the documentation for gc_stale_time is incorrect here.
# It is not a check interval at all, but just a time used to consider an
# entry "dead" if unused.  Fine, but it seems entries are "unused" unless
# there is a route cache entry (?) referring to it (eg: "ref" in "ip -s
# neigh") which gets flushed often because of BGP changes.  Whew.  So,
# make gc_stale_time high for now.

# Lower the check interval.  This just makes things smoother and helps
# make ARP expiry more predictable.

echo 5 > default/gc_interval	# What appears to really be the check interval [dfl: 30]
echo 300 > default/gc_stale_time # "Check interval for stale neigh entries", but actually the gc_staletime [dfl: 60]

echo 512 > default/gc_thresh1	# Neighbour table low watermark (no gc) [dfl: 128]
echo 4096 > default/gc_thresh2	# Neighbour table medium watermark (gc at gc_interval) [dfl: 512]
echo 8192 > default/gc_thresh3	# Neighbour table high watermark (always gc) [dfl: 1024]

# Routing tweaks

cd ../route

# Since kernel 2.4.21 (and 2.4.22-pre1), these tweaks have become unnecessary
# due to optimizations resulting from a thread started on linux-net regarding
# forwarding efficiency.  gc_min_interval now defaults to 0.5 (will show as "0"
# via proc), and the internals have been changed to quickly recycle entries
# when required (when forwarding random src/dst traffic).
# The only change we make now is to decrease gc_elasticity which has been
# somewhat overloaded as a "maximum number of entries per hash bucket" garbage
# collection trigger.  By keeping this low, we recycle entries faster without
# slowing lookups during a DoS attack.

echo 3 > gc_elasticity		# Higher is weaker, 0 will nuke all [dfl: 8]
echo 16384 > gc_thresh		# Threshold where GC starts [dfl: depends on hash size/RAM: 4096]
echo 86400 > secret_interval	# rtcache secret rehash time (whatever) [dfl: 600]

exit 0