Re: Supporting 4 way connections in LKSCTP

From: Sun Paul
Date: Mon Dec 02 2013 - 20:40:01 EST

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Another question

if a wrong source IP is used, does the association still classified as normal?

On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@xxxxxxxxx> wrote:
> Thanks Vlad
>
> I checked on the route, and it looks correct.
>
> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
> cache mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
> cache mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
> cache mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
> cache mtu 1500 advmss 1460 hoplimit 64
>
> so, if this is not being handled in LKSCTP, is it possible to suggest
> a way how we can achieve it?
>
> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@xxxxxxxxx> wrote:
>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@xxxxxxxxx> 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@localhost ~]# 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@localhost ~]# 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.
>>
>> 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@xxxxxxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx> 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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>>>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
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>>>>>>>>>>
>>>>>>>>>
>>>>>>> --
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>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>
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>>
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