[ovs-dev] [ovn] problem: long tcp session instantiation with stateful ACLs
Vladislav Odintsov
odivlad at gmail.com
Thu Sep 16 14:18:48 UTC 2021
Sorry, by OOT I meant non-inbox kmod.
I’ve tried to use inbox kernel module (from kernel package) and problem resolved.
Regards,
Vladislav Odintsov
> On 16 Sep 2021, at 17:17, Vladislav Odintsov <odivlad at gmail.com> wrote:
>
> Hi Dumitru,
>
> I’ve tried to exclude OOT OVS kernel module.
> With OVN 20.06.3 + OVS 2.13.4 the problem solved.
>
> Could you please try with OOT kmod? For me it looks like a bug in OOT OVS kernel module code.
>
> Thanks.
>
> Regards,
> Vladislav Odintsov
>
>> On 16 Sep 2021, at 11:02, Dumitru Ceara <dceara at redhat.com <mailto:dceara at redhat.com>> wrote:
>>
>> On 9/16/21 2:50 AM, Vladislav Odintsov wrote:
>>> Hi Dumitru,
>>>
>>> thanks for your reply.
>>>
>>> Regards,
>>> Vladislav Odintsov
>>>
>>>> On 15 Sep 2021, at 11:24, Dumitru Ceara <dceara at redhat.com> wrote:
>>>>
>>>> Hi Vladislav,
>>>>
>>>> On 9/13/21 6:14 PM, Vladislav Odintsov wrote:
>>>>> Hi Numan,
>>>>>
>>>>> I’ve checked with OVS 2.16.0 and OVN master. The problem persists.
>>>>> Symptoms are the same.
>>>>>
>>>>> # grep ct_zero_snat /var/log/openvswitch/ovs-vswitchd.log
>>>>> 2021-09-13T16:10:01.792Z|00019|ofproto_dpif|INFO|system at ovs-system: Datapath supports ct_zero_snat
>>>>
>>>> This shouldn't be related to the problem we fixed with ct_zero_snat.
>>>>
>>>>>
>>>>> Regards,
>>>>> Vladislav Odintsov
>>>>>
>>>>>> On 13 Sep 2021, at 17:54, Numan Siddique <numans at ovn.org> wrote:
>>>>>>
>>>>>> On Mon, Sep 13, 2021 at 8:10 AM Vladislav Odintsov <odivlad at gmail.com <mailto:odivlad at gmail.com>> wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> we’ve encountered a next problem with stateful ACLs.
>>>>>>>
>>>>>>> Suppose, we have one logical switch (ls1) and attached to it a VIF type logical ports (lsp1, lsp2).
>>>>>>> Each logical port has a linux VM besides it.
>>>>>>>
>>>>>>> Logical ports reside in port group (pg1) and two ACLs are created within this PG:
>>>>>>> to-lport outport == @pg1 && ip4 && ip4.dst == 0.0.0.0/0 allow-related
>>>>>>> from-lport outport == @pg1 && ip4 && ip4.src == 0.0.0.0/0 allow-related
>>>>>>>
>>>>>>> When we have a high-connection rate service between VMs, the tcp source/dest ports may be reused before the connection is deleted from LSP’s-related conntrack zones on the host.
>>>>>>> Let’s use curl with passing --local-port argument to have each time same source port.
>>>>>>>
>>>>>>> Run it from VM to another VM (172.31.0.18 -> 172.31.0.17):
>>>>>>> curl --local-port 44444 http://172.31.0.17/
>>>>>>>
>>>>>>> Check connections in client’s and server’s vif zones (client - zone=20, server - zone=1):
>>>>>>> run while true script to check connections state per-second, while running new connection with same source/dest 5-tuple:
>>>>>>>
>>>>>>> while true; do date; grep -e 'zone=1 ' -e zone=20 /proc/net/nf_conntrack; sleep 0.2; done
>>>>>>>
>>>>>>> Right after we’ve succesfully run curl, the connection is getting time-closed and next time-wait states:
>>>>>>>
>>>>>>> Mon Sep 13 14:34:39 MSK 2021
>>>>>>> ipv4 2 tcp 6 59 CLOSE_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=1 use=2
>>>>>>> ipv4 2 tcp 6 59 CLOSE_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=20 use=2
>>>>>>> Mon Sep 13 14:34:39 MSK 2021
>>>>>>> ipv4 2 tcp 6 119 TIME_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=1 use=2
>>>>>>> ipv4 2 tcp 6 119 TIME_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=20 use=2
>>>>>>>
>>>>>>> And it remains in time-wait state for nf_conntrack_time_wait_timeout (120 seconds for centos 7).
>>>>>>>
>>>>>>> Everything is okay for now.
>>>>>>> While we have installed connections in TW state in zone 1 and 20, lets run this curl (source port 44444) again:
>>>>>>> 1st SYN packet is lost. It didn’t get to destination VM. In conntrack we have:
>>>>>>>
>>>>>>> Mon Sep 13 14:34:41 MSK 2021
>>>>>>> ipv4 2 tcp 6 118 TIME_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=1 use=2
>>>>>>>
>>>>>>> We see that TW connection was dropped in source vif’s zone (20).
>>>>>>>
>>>>>>> Next, after one second TCP sends retry and connection in destination (server’s) zone is dropped and a new connection is created in source zone (client’s):
>>>>>>>
>>>>>>> Mon Sep 13 14:34:41 MSK 2021
>>>>>>> ipv4 2 tcp 6 120 SYN_SENT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 [UNREPLIED] src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 mark=0 zone=20 use=2
>>>>>>>
>>>>>>> Server VM still didn’t get this SYN packet. It got dropped.
>>>>>>>
>>>>>>> Then, after 2 seconds TCP sends retry again and connection is working well:
>>>>>>>
>>>>>>> Mon Sep 13 14:34:44 MSK 2021
>>>>>>> ipv4 2 tcp 6 59 CLOSE_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=1 use=2
>>>>>>> ipv4 2 tcp 6 59 CLOSE_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=20 use=2
>>>>>>> Mon Sep 13 14:34:44 MSK 2021
>>>>>>> ipv4 2 tcp 6 119 TIME_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=1 use=2
>>>>>>> ipv4 2 tcp 6 119 TIME_WAIT src=172.31.0.18 dst=172.31.0.17 sport=44444 dport=80 src=172.31.0.17 dst=172.31.0.18 sport=80 dport=44444 [ASSURED] mark=0 zone=20 use=2
>>>>>>>
>>>>>>> I guess, that it could happen:
>>>>>>> 1. Run curl with an empty conntrack zones. Everything is good, we’ve got http response, closed the connection. There’s one TW entry in client’s and one in server’s zonntrack zones.
>>>>>>> 2. Run curl with same source port within nf_conntrack_time_wait_timeout seconds.
>>>>>>> 2.1. OVS gets packet from VM, sends it to client’s conntrack zone=20. It matches pre-existed conntrack entry in tw state from previous curl run. TW connection in conntrack is deleted. A copy of a packet is returned to OVS and recirculated packet has ct.inv (?) and !ct.trk states and got dropped (I’m NOT sure, it’s just an assumption!)
>>>>>>> 3. After one second client VM resends TCP SYN.
>>>>>>> 3.1. OVS gets packet, sends through client’s conntrack zone=20, a new connection is added, packet has ct.trk and ct.new states set. Packet goes to recirculation.
>>>>>>> 3.2. OVS sends packet to server’s conntrack zone=1. It matches pre-existed conntrack entry in tw state from previous run. Conntrack removes this entry. Packet is returned to OVS with ct.inv (?) and !ct.trk. Packet got dropped.
>>>>>>> 4. Client’s VM again sends TCP SYN after 2 more seconds left.
>>>>>>> 4.1 OVS gets packet from client’s VIF, sends to client’s conntrack zone=20, it matches pre-existed SYN_SENT conntrack entry state, packets is returned to OVS with ct.new, ct.trk flags set.
>>>>>>
>>>>>>
>>>>>>> 4.2 OVS sends packet to server’s conntrack zone=1. Conntrack table for zone=1 is empty, it adds new entry, returns packet to OVS with ct.trk and ct.new flags set.
>>>>>>> 4.3 OVS sends packet to server’s VIF, next traffic operates normally.
>>>>>>>
>>>>>>> So, with such behaviour connection establishment sometimes takes up to three seconds (2 TCP SYN retries) and makes troubles in overlay services. (Application timeouts and service outages).
>>>>>>>
>>>>>>> I’ve checked how conntrack works inside VMs with such traffic and it looks like if conntrack gets a packet within a TW connection it recreates a new conntrack entry. No tuning inside VMs was performed. As a server I used apache with default config from CentOS distribution.
>>>>
>>>> I don't have a centos 7 at hand but I do have a rhel 7
>>>> (3.10.0-1160.36.2.el7.x86_64) and I didn't manage to hit the issue you
>>>> reported here (using OVS and OVN upstream master). The SYN matching the
>>>> conntrack entry in state TIME_WAIT moves the entry to NEW and seems to
>>>> be forwarded just fine, the session afterwards go to ESTABLISHED.
>>>>
>>>> Wed Sep 15 04:18:35 AM EDT 2021
>>>> conntrack v1.4.5 (conntrack-tools): 7 flow entries have been shown.
>>>> tcp 6 431930 ESTABLISHED src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=6 use=1
>>>> tcp 6 431930 ESTABLISHED src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=3 use=1
>>>> --
>>>> Wed Sep 15 04:18:36 AM EDT 2021
>>>> conntrack v1.4.5 (conntrack-tools): 7 flow entries have been shown.
>>>> tcp 6 119 TIME_WAIT src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=6 use=1
>>>> tcp 6 119 TIME_WAIT src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=3 use=1
>>>> --
>>>> Wed Sep 15 04:18:38 AM EDT 2021
>>>> conntrack v1.4.5 (conntrack-tools): 7 flow entries have been shown.
>>>> tcp 6 431999 ESTABLISHED src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=6 use=1
>>>> tcp 6 431999 ESTABLISHED src=42.42.42.2 dst=42.42.42.3 sport=4141
>>>> dport=4242 src=42.42.42.3 dst=42.42.42.2 sport=4242 dport=4141 [ASSURED]
>>>> mark=0 secctx=system_u:object_r:unlabeled_t:s0 zone=3 use=1
>>>> --
>>>>
>>>> DP flows just after the second session is initiated also seem to confirm
>>>> that everything is fine:
>>>>
>>>> # ovs-appctl dpctl/dump-flows | grep -oE "ct_state(.*),ct_label"
>>>> ct_state(+new-est-rel-rpl-inv+trk),ct_label
>>>> ct_state(-new+est-rel-rpl-inv+trk),ct_label
>>>> ct_state(-new+est-rel+rpl-inv+trk),ct_label
>>>> ct_state(+new-est-rel-rpl-inv+trk),ct_label
>>>> ct_state(-new+est-rel+rpl-inv+trk),ct_label
>>>> ct_state(-new+est-rel-rpl-inv+trk),ct_label
>>>>
>>>> I also tried it out on a Fedora 34 with 5.13.14-200.fc34.x86_64, still
>>>> works fine.
>>>>
>>>> What kernel and openvswitch module versions do you use?
>>>>
>>> On my box there is CentOS 7.5 with kernel 3.10.0-862.14.4.el7 and OOT kernel module.
>>> I’ve tested two versions, in both the problem was hit:
>>> openvswitch-kmod-2.13.4-1.el7_5.x86_64
>>> openvswitch-kmod-2.16.0-1.el7_5.x86_64
>>>
>>> Do you think the problem could be related to kernel (conntrack) and kernel must be upgraded here?
>>> Or, maybe I should try master OVS, as you did?
>>
>> I just tried with OVS v2.13.4, OVN master and it all worked fine (both
>> on Fedora 34 and rhel 7). I don't think the problem is in user space.
>>
>> Regards,
>> Dumitru
>>
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