if we do not specific the gateway, it will be a problem. One of the reason why it is like that is due to that the server do not know which source IP should be used to send out the query. [root@localhost ~]# ip route get 12.1.1.1 RTNETLINK answers: Network is unreachable [root@localhost ~]# ip route get 11.1.1.1 RTNETLINK answers: Network is unreachable On Tue, Dec 3, 2013 at 10:02 AM, Vlad Yasevich <vyasevich@xxxxxxxxx> wrote: > On 12/02/2013 08:31 PM, Sun Paul 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? > > Like I said before lksctp only iterates over the bound address > list if the source address from the route returned by the kernel > does not match the bound address list. > > To simulate the algorithm with with ip route get, you'd > get something like this: > > ip route get 11.1.1.1 > if from_address not in bound address list > for each bound_addr in bound address list > ip route get 11.1.1.1 from bound_addr > > The kernel will almost always give you a valid route even if the > from address does not belong to the expected interface. > > So, in your case, what does a simple ip route get 11.1.1.1 return? > That's the address that will be used to talk to 11.1.1.1 by default. > > -vlad >> >> 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 >>>>>>>>>>> -- >>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in >>>>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>>>>>>>>> >>>>>>>>>> >>>>>>>> -- >>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in >>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>>>>>> >>>>> >>>>> -- >>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in >>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
