[ovs-dev] [PATCH] conntrack: document NULL SNAT behavior and add a test case
Eelco Chaudron
echaudro at redhat.com
Tue Mar 23 08:52:05 UTC 2021
On 22 Mar 2021, at 19:50, Paolo Valerio wrote:
> Hi Eelco,
>
> Thanks for working on this, very useful indeed.
> not a full review, but I have a question about a minor thing.
>
> Eelco Chaudron <echaudro at redhat.com> writes:
>
>> Currently, conntrack in the kernel has an undocumented feature
>> referred
>> to as NULL SNAT. Basically, when a source port collision is detected
>> during the commit, the source port will be translated to an ephemeral
>> port. If there is no collision, no SNAT is performed.
>>
>> This patchset documents this behavior and adds a self-test to verify
>> it's not changing.
>>
>> Signed-off-by: Eelco Chaudron <echaudro at redhat.com>
>> ---
>> lib/ovs-actions.xml | 10 ++++++++
>> tests/system-kmod-macros.at | 7 ++++++
>> tests/system-traffic.at | 45
>> ++++++++++++++++++++++++++++++++++++++
>> tests/system-userspace-macros.at | 10 ++++++++
>> 4 files changed, 72 insertions(+)
>>
>> diff --git a/lib/ovs-actions.xml b/lib/ovs-actions.xml
>> index a2778de4b..a0070e6c6 100644
>> --- a/lib/ovs-actions.xml
>> +++ b/lib/ovs-actions.xml
>> @@ -1833,6 +1833,16 @@ for <var>i</var> in [1,<var>n_members</var>]:
>> connection, will behave the same as a bare
>> <code>nat</code>.
>> </p>
>>
>> + <p>
>> + For SNAT, there is a special case when the
>> <code>src</code> IP
>> + address is configured as all 0's, i.e.,
>> + <code>nat(src=0.0.0.0)</code>. In this case, when a
>> source port
>> + collision is detected during the commit, the source port
>> will be
>> + translated to an ephemeral port. If there is no
>> collision, no SNAT
>> + is performed. Note that this is currently only
>> implemented in the
>> + Linux kernel datapath.
>> + </p>
>> +
>> <p>
>> Open vSwitch 2.6 introduced <code>nat</code>. Linux 4.6
>> was the
>> earliest upstream kernel that implemented
>> <code>ct</code> support for
>> diff --git a/tests/system-kmod-macros.at
>> b/tests/system-kmod-macros.at
>> index 15628a7c6..38bb1c55c 100644
>> --- a/tests/system-kmod-macros.at
>> +++ b/tests/system-kmod-macros.at
>> @@ -99,6 +99,13 @@ m4_define([CHECK_CONNTRACK_FRAG_OVERLAP],
>> #
>> m4_define([CHECK_CONNTRACK_NAT])
>>
>> +# CHECK_CONNTRACK_NULL_SNAT()
>> +#
>> +# Perform requirements checks for running conntrack SNAT NULL tests.
>> +# The kernel always supports NULL SNAT, so no check is needed.
>> +#
>> +m4_define([CHECK_CONNTRACK_NULL_SNAT])
>> +
>> # CHECK_CONNTRACK_TIMEOUT()
>> #
>> # Perform requirements checks for running conntrack customized
>> timeout tests.
>> diff --git a/tests/system-traffic.at b/tests/system-traffic.at
>> index fb5b9a36d..1be425bb4 100644
>> --- a/tests/system-traffic.at
>> +++ b/tests/system-traffic.at
>> @@ -4433,6 +4433,51 @@
>> tcp,orig=(src=10.1.1.1,dst=10.1.1.2,sport=<cleared>,dport=<cleared>),reply=(src=
>> OVS_TRAFFIC_VSWITCHD_STOP
>> AT_CLEANUP
>>
>> +
>> +AT_SETUP([conntrack - NULL SNAT])
>> +AT_SKIP_IF([test $HAVE_NC = no])
>> +CHECK_CONNTRACK()
>> +CHECK_CONNTRACK_NULL_SNAT()
>> +OVS_TRAFFIC_VSWITCHD_START()
>> +
>> +ADD_NAMESPACES(at_ns0, at_ns1)
>> +ADD_VETH(p0, at_ns0, br0, "10.1.1.1/24")
>> +ADD_VETH(p1, at_ns1, br0, "10.1.1.2/24")
>> +NS_CHECK_EXEC([at_ns0], [ip route add 172.1.1.0/24 via 10.1.1.2])
>> +
>> +OVS_START_L7([at_ns1], [http])
>> +
>
> I noticed you use nc clients, is there any specific reason you
> preferred
> httpd over something like:
>
> NETNS_DAEMONIZE([at_ns1], [nc -l -k 80 > /dev/null], [nc0.pid])
No specific reason other than the http server python script was used in
all the other tests above.
>> +AT_DATA([flows.txt], [dnl
>> +table=0,priority=30,ct_state=-trk,ip,action=ct(table=0)
>> +table=0,priority=20,ip,nw_dst=10.1.1.0/24,actions=ct(commit,nat(src=0.0.0.0),table=10)
>> +table=0,priority=20,ip,nw_dst=172.1.1.2,actions=ct(commit,nat(dst=10.1.1.2),table=10)
>> +table=0,priority=10,arp,action=normal
>> +table=0,priority=1,action=drop
>> +table=10,priority=20,ct_state=+rpl,ip,nw_dst=10.1.1.0/24
>> actions=ct(table=20,nat)
>> +table=10,priority=10,ip,nw_dst=10.1.1.0/24 actions=resubmit(,20)
>> +table=20,priority=10,ip,nw_dst=10.1.1.1,action=1
>> +table=20,priority=10,ip,nw_dst=10.1.1.2,action=2
>> +])
>> +AT_CHECK([ovs-ofctl --bundle add-flows br0 flows.txt])
>> +
>> +dnl - Test to make sure src nat is NOT done when not needed
>> +NS_CHECK_EXEC([at_ns0], [echo "TEST" | nc -p 30000 10.1.1.2 80 >
>> nc-1.log])
>> +AT_CHECK([ovs-appctl dpctl/dump-conntrack | grep
>> "orig=.src=10\.1\.1\.1,"], [0], [dnl
>> +tcp,orig=(src=10.1.1.1,dst=10.1.1.2,sport=30000,dport=80),reply=(src=10.1.1.2,dst=10.1.1.1,sport=80,dport=30000),protoinfo=(state=TIME_WAIT)
>> +])
>> +
>> +dnl - Test to make sure src nat is done when needed
>> +NS_CHECK_EXEC([at_ns0], [echo "TEST2" | nc -p 30001 172.1.1.2 80 >
>> nc-2.log])
>> +NS_CHECK_EXEC([at_ns0], [echo "TEST3" | nc -p 30001 10.1.1.2 80 >
>> nc-3.log])
>> +AT_CHECK([ovs-appctl dpctl/dump-conntrack | grep 30001 | grep
>> "orig=.src=10\.1\.1\.1," | sed -e 's/port=30001/port=<clnt_s_port>/g'
>> -e 's/sport=80,dport=[[0-9]]\+/sport=80,dport=<rnd_port>/g' | sort],
>> [0], [dnl
>> +tcp,orig=(src=10.1.1.1,dst=10.1.1.2,sport=<clnt_s_port>,dport=80),reply=(src=10.1.1.2,dst=10.1.1.1,sport=80,dport=<rnd_port>),protoinfo=(state=TIME_WAIT)
>> +tcp,orig=(src=10.1.1.1,dst=172.1.1.2,sport=<clnt_s_port>,dport=80),reply=(src=10.1.1.2,dst=10.1.1.1,sport=80,dport=<clnt_s_port>),protoinfo=(state=TIME_WAIT)
>> +])
>> +
>> +OVS_TRAFFIC_VSWITCHD_STOP
>> +AT_CLEANUP
>> +
>> +
>> AT_SETUP([conntrack - simple DNAT])
>> CHECK_CONNTRACK()
>> CHECK_CONNTRACK_NAT()
>> diff --git a/tests/system-userspace-macros.at
>> b/tests/system-userspace-macros.at
>> index 34f82cee3..71acc8618 100644
>> --- a/tests/system-userspace-macros.at
>> +++ b/tests/system-userspace-macros.at
>> @@ -96,6 +96,16 @@ m4_define([CHECK_CONNTRACK_FRAG_OVERLAP])
>> #
>> m4_define([CHECK_CONNTRACK_NAT])
>>
>> +# CHECK_CONNTRACK_NULL_SNAT()
>> +#
>> +# Perform requirements checks for running conntrack SNAT NULL tests.
>> +# The userspace datapath does not support NULL SNAT.
>> +#
>> +m4_define([CHECK_CONNTRACK_NULL_SNAT],
>> +[
>> + AT_SKIP_IF([:])
>> +])
>> +
>> # CHECK_CONNTRACK_TIMEOUT()
>> #
>> # Perform requirements checks for running conntrack customized
>> timeout tests.
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