Rate limiting made simple

I use CrashPlan as a backup service. It works and is very simple to set up, but has limited options for controlling bandwidth. In fact, if you’re running it on a headless system (e.g., a fileserver of some sort), your options are effectively “too slow” and “CONSUME EVERYTHING”. There is an open request to add time-based limitations to the application itself, but for now I’ve solved this using a very simple traffic shaping configuration. Because the learning curve for “tc” and friends is surprisingly high, I’m putting my script here in the hopes that other people might find it useful, and so that I can find it when I need to do this again someday.

#!/bin/sh
 
# The network device used for backups
dev=p10p1
 
# The remove address of the CrashPlanserver
crashplan_addr=50.93.246.1
 
# The port
crashplan_port=443
 
# The rate limit. See tc(8) for acceptable syntax.
crashplan_limit=2mbit
 
if [ "$1" = "enable" ]; then
    #
    # This creates and activates the traffic shaper
    # configuration.
    #
    logger -s -t ratelimit -p user.notice "enabling rate limits"
    tc qdisc del dev $dev root > /dev/null 2>&1
    tc qdisc add dev $dev root handle 1: htb
    tc class add dev $dev parent 1: classid 1:10 htb rate $crashplan_limit
    tc filter add dev $dev parent 1: prio 0 protocol ip handle 10 fw flowid 1:10
    iptables -t mangle -A OUTPUT -d $crashplan_addr -p tcp --dport $crashplan_port -j MARK --set-mark 10
elif [ "$1" = "disable" ]; then
    #
    # This removes the traffic shaper
    # configuration.
    #
    logger -s -t ratelimit -p user.notice "disabling rate limits"
    tc qdisc del dev $dev root > /dev/null 2>&1
    iptables -t mangle -D OUTPUT -d $crashplan_addr -p tcp --dport $crashplan_port -j MARK --set-mark 10
elif [ "$1" = "show" ]; then
    #
    # Shows the current traffic shaper configuration.
    #
    tc qdisc show dev $dev
    tc class show dev $dev
    tc filter show dev $dev
    iptables -t mangle -vnL OUTPUT
fi