Message-ID: <CAGugRbXBDy2kt6NxZ6n2+UcpT=RqZSBq1aaDm-VwVYokjAnTpw@mail.gmail.com>
Date:	Mon, 2 Dec 2013 12:10:26 -0500
From:	Karl Heiss <kheiss@...il.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Sun Paul <paulrbk@...il.com>, Neil Horman <nhorman@...driver.com>,
	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Supporting 4 way connections in LKSCTP

On Mon, Dec 2, 2013 at 11:42 AM, Vlad Yasevich <vyasevich@...il.com> wrote:
> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@...il.com> wrote:
>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>> HB_ACK? below is the testing result where a router is located in the
>>>> middle.
>>>>
>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>
>>>> eth1
>>>> 0 packets dropped by kernel
>>>> [root@...alhost ~]# tcpdump -i eth1 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>> 11:24:14.539486
>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>
>>>> eth2
>>>> [root@...alhost ~]# tcpdump -i eth2 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>
>>>> When starting the application. the packet show as below.
>>>>
>>>> eth1
>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>
>>>> eth2
>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>> 2330749678]
>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>
>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>
>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>
>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>
>>>> eth1
>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 12, length 64
>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 12, length 64
>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 13, length 64
>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 13, length 64
>>>>
>>>> eth2
>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 2, length 64
>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 2, length 64
>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 3, length 64
>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 3, length 64
>>>>
>>>> Below is the route information
>>>> #route -n
>>>> Kernel IP routing table
>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>
>>>> # ip route show
>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>
>>>> Since we are using iproute2, so we will have dedicate routing table
>>>> per interface
>>>>
>>>> # ip route show table SCTP1
>>>> default via 110.1.1.254 dev eth1
>>>>
>>>> # ip route show table SCTP2
>>>> default via 120.1.1.254 dev eth2
>>>>
>>>> # ip rule ls
>>>> 0: from all lookup local
>>>> 101: from 110.1.1.1 lookup SCTP1
>>>> 102: from 120.1.1.1 lookup SCTP2
>>>> 32766: from all lookup main
>>>> 32767: from all lookup default
>>>>
>>>> How LKSCTP select source address to reply? If we know how it works,
>>>> then we may know what is going wrong.
>>>
>>> LKSCTP will prefer the address returned from the routing table as long
>>> as it is one of the addresses that is bound by the socket and are usable
>>> by the association.
>>>
>>> If the address returned from the route lookup is not part of the
>>> association, then lksctp attempts to lookup routes using one of the
>>> source addresses it has available.  Usually the first lookup succeeds
>>> due to the host-model implementation in linux.
>>>
>>> You may want to change your rule set to be destination based.  Then
>>> in the table associated with the rule, specify the source address
>>> you want to be used.
>>>
>>> -vlad
>>
>> I have had similar qualms myself about this behavior, and I honestly
>> don't know what the correct answer should be...
>>
>> In my opinion, shouldn't the source address "just work" for
>> acknowledgements? If the spec explicitly states that the ACK should
>> have a source address that matches the destination of the chunk being
>> ACKed, why should someone have to configure this behavior outside of
>> the SCTP stack by default? Is it a technical limitation, or is this
>> done for a particular reason?  I can understand needing to override
>> the behavior, but why isn't the default "sane"?
>
> I think the results are sane, they simply may not match expectations.
> SCTP spec doesn't say anything about source address selection.  It
> says that a response should be send back to the source of the request.
> This is being done in both cases, i.e. the destination address in
> INIT-ACK matches the source of the INIT.
>
> The spec does contain the MAY text that allows finer control of source
> addresses, but lksctp doesn't seem to implement that.  Whenever we've
> tried, we couldn't get the generic mechanism working to please everyone,
> as everyone had slightly different configurations and expectations.  So
> we left it to the rules engine.
>

Oops!  You are correct.  I must have accidentally read it as a SHOULD.. ;-)

Thanks for the history on previous attempts.  I had always wondered about this.

Karl

> In this setup, it just appears that the default routing is not what you
> expect.  You can easily check this with 'ip route get' command.  If it
> is not what you want linux allows you to change that via ip rules.
>
> -vlad
>
>>
>> Karl
>>
>>>>
>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@...driver.com> wrote:
>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>> Hi Vlad
>>>>>>
>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>
>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>
>>>>>> In the single-homing sample that provided in the original email, both
>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>> respond to the SCTP request.
>>>>>>
>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>> and in both lookups, the route indicates that only one source address should be
>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>> and interface be used.
>>>>>
>>>>> Neil
>>>>>
>>>>>> - PS
>>>>>>
>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@...il.com> wrote:
>>>>>>> Hi Vlad
>>>>>>>
>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>
>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>> respond to the SCTP request.
>>>>>>>
>>>>>>> - PS
>>>>>>>
>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@...il.com> wrote:
>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>
>>>>>>>>> Configuration
>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>> IP-B (eth2)
>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>> IP-Y (eth2)
>>>>>>>>>
>>>>>>>>
>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>> be used to connect to the remote.
>>>>>>>>
>>>>>>>>> the four way paths are shown below.
>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>
>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>
>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>> is what it is going to use.
>>>>>>>>
>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>
>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>> on the destination address.
>>>>>>>>
>>>>>>>> -vlad
>>>>>>>>
>>>>>>>>>
>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>
>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>
>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>
>>>>>>>>> TCP trace on eth1
>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> TCP trace on eth2
>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>> 3340756356]
>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>
>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>> 1877695021]
>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>
>>>>>>>>> Thanks
>>>>>>>>>
>>>>>>>>> PS
>>>>>>>>> --
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>>>>>>>>>
>>>>>>>>
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>>>>>>
>>>
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