Re: dummynet configuration for automated tests

From: Kristof Provost <kp_at_FreeBSD.org>
Date: Sun, 25 Jul 2021 17:57:59 +0200
Perhaps a different question would also be helpful:

Can anyone share a functional example configuration using dummynet to 
prioritise traffic?

Thanks,
Kristof

On 20 Jul 2021, at 9:15, Kristof Provost wrote:

> Hi,
>
> I’ve been trying (and failing) to write a few basic test cases for 
> dummynet (with ipfw for now).
>
> The full test script can be found here: 
> https://people.freebsd.org/~kp/dummynet.sh but the relevant bit is 
> this:
>
> 	queue_v6_body()
> 	{
> 	        fw=$1
> 	        firewall_init $fw
> 	        dummynet_init $fw
>
> 	        epair=$(vnet_mkepair)
> 	        epair_link=$(vnet_mkepair)
> 	        vnet_mkjail alcatraz ${epair}b ${epair_link}a
> 	        vnet_mkjail srv ${epair_link}b
>
> 	set -x
>
> 	        ifconfig ${epair}a inet6 2001:db8:42::1/64 no_dad up
> 	        route add -6 2001:db8:43::/64 2001:db8:42::2
>
> 	        jexec alcatraz ifconfig ${epair}b inet6 2001:db8:42::2 no_dad 
> up
> 	        jexec alcatraz ifconfig ${epair_link}a inet6 2001:db8:43::2 
> no_dad up
> 	        jexec alcatraz sysctl net.inet6.ip6.forwarding=1
>
> 	        jexec srv ifconfig ${epair_link}b inet6 2001:db8:43::1 no_dad 
> up
> 	        jexec srv route add -6 default 2001:db8:43::2
> 	        jexec srv /usr/sbin/inetd -p inetd-alcatraz.pid \
> 	            $(atf_get_srcdir)/../pf/echo_inetd.conf
>
> 	        # Sanity check
> 	        atf_check -s exit:0 -o ignore ping6 -i .1 -c 3 -s 1200 
> 2001:db8:42::2
> 	        atf_check -s exit:0 -o ignore ping6 -i .1 -c 3 -s 1200 
> 2001:db8:43::2
> 	        atf_check -s exit:0 -o ignore ping6 -i .1 -c 3 -s 1200 
> 2001:db8:43::1
>
> 	        reply=$(echo "foo" | nc -w 5 -N 2001:db8:43::1 7)
> 	        if [ "$reply" != "foo" ];
> 	        then
> 	                atf_fail "Echo sanity check failed"
> 	        fi
>
> 	        jexec alcatraz dnctl pipe 1 config bw 300Byte/s queue 5 mask 
> proto 0xff
> 	        jexec alcatraz dnctl sched 1 config pipe 1 type wf2q+ mask 
> proto 0xff
> 	        jexec alcatraz dnctl queue 1 config sched 1 weight 99 queue 5 
> mask proto 0xff
> 	        jexec alcatraz dnctl queue 2 config sched 1 weight 1 queue 5 
> mask proto 0xff
>
> 	        firewall_config alcatraz ${fw} \
> 	                "ipfw"  \
> 	                        "ipfw add queue 2 ipv6-icmp from any to any 
> icmp6types 128,129" \
> 	                        "ipfw add queue 1 tcp from any to any"
>
> 	        # Single ping succeeds
> 	        atf_check -s exit:0 -o ignore ping6 -c 3 2001:db8:43::1
> 	        # Unsaturated TCP succeeds
> 	        reply=$(echo "foo" | nc -w 5 -N 2001:db8:43::1 7)
> 	        if [ "$reply" != "foo" ];
> 	        then
> 	                atf_fail "Unsaturated echo failed"
> 	        fi
>
> 	        # Saturate the link
> 	        ping6 -i .01 -s 1200 2001:db8:43::1 &
>
> 	        # Give that a chance to fill the queue & pipe
> 	        sleep 1
>
> 	        jexec alcatraz ipfw show
>
> 	        # We should now be hitting the limits and get this packet 
> dropped.
> 	        atf_check -s exit:2 -o ignore ping6 -c 1 -W 1 -s 1200 
> 2001:db8:43::1
>
> 	        # TCP should still just pass
> 	        for i in `seq 0 4`
> 	        do
> 	                reply=$(echo "foo $i" | nc -w 10 -N 2001:db8:43::1 7)
> 	                if [ "$reply" != "foo $i" ];
> 	                then
> 	                        atf_fail "Failed to prioritise traffic on 
> interation $i"
> 	                fi
> 	                sleep 1
> 	        done
>
> 	        jexec alcatraz ipfw flush
> 	        # This will fail if we don't differentiate the traffic
> 	        firewall_config alcatraz ${fw} \
> 	                "ipfw"  \
> 	                        "ipfw add queue 1 ipv6-icmp from any to any 
> icmp6types 128,129" \
> 	                        "ipfw add queue 2 tcp from any to any"
>
> 	        # Carry over state?
> 	        killall ping6
> 	        ping6 -i .01 -s 1200 2001:db8:43::1 &
> 	        sleep 1
>
> 	        reply=$(echo "baz" | nc -w 10 -N 2001:db8:43::1 7)
> 	        if [ "$reply" == "baz" ];
> 	        then
> 	                jexec alcatraz ipfw show
> 	                atf_fail "TCP still made it through, even when not 
> prioritised"
> 	        fi
> 	}
>
> The idea is to set up a very slow link (using a pipe), and then to 
> send both ICMP echo and TCP traffic through it. There’s vastly more 
> ICMP traffic than TCP, and the expectation is that without 
> prioritisation the ICMP traffic will drown out TCP and cause the 
> connection to fail.
> We then try to use dummynet to give TCP priority over ICMP, so that 
> the TCP connections do succeed.
>
> However, I simply cannot get it to behave in any sort of predictable 
> or consistent way. Sometimes the TCP connection succeeds, despite 
> attempts to prioritise ICMP, or vice versa.
>
> Clearly I’m misconfiguring something, but at this point I do not 
> understand what. Does anyone see my mistake, or have any relevant 
> configuration examples to share?
>
> Thanks,
> Kristof
Received on Sun Jul 25 2021 - 15:57:59 UTC

Original text of this message