This issue appears to be an upstream bug, since you tested the latest upstream kernel. Would it be possible for you to open an upstream bug report[0]? That will allow the upstream Developers to examine the issue, and may provide a quicker resolution to the bug.
Please follow the instructions on the wiki page[0]. The first step is to email the appropriate mailing list. If no response is received, then a bug may be opened on bugzilla.kernel.org. Once this bug is reported upstream, please add the tag: 'kernel-bug- reported-upstream'. [0] https://wiki.ubuntu.com/Bugs/Upstream/kernel ** Changed in: linux (Ubuntu) Status: Confirmed => Triaged -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1681847 Title: IPVS incorrectly reverse-NATs traffic to LVS host Status in linux package in Ubuntu: Triaged Bug description: We have observed the following behaviour on our LVS systems, which is causing issues with our monitor scripts. The systems are running Ubuntu 14.04.5 LTS and I've tested both with the stock 3.13.0 kernel (-100 and -116) and the 4.4.0-72 xenial kernel. Our systems are set up in direct routing mode for the services they handle. Our monitor scripts for DNS send test queries to our DNS servers using their real IPs. Sporadically, we have seen these checks fail as the DNS answers are coming back from the wrong IP address. We debugged this using tcpdump, and found that the response packets coming into the LVS systems were using the correct IPs (i.e. the real IPs on the DNS servers). However, applications see the responses as coming from a VIP instead. All of this has been established using UDP traffic. I have tracked this behaviour down to a specific case, which I can only assume is associated with how the kernel handles LVS NAT connections (i.e. masquerade mode): - If a DNS query is made on the LVS server to a DNS VIP, that creates an entry in the connection table, and is keyed on (srcip:sport -> dstip:dport) and associated with (vip:vport) - for example, (lvsip:50000 -> dnsip:53) associated with (dnsvip:53) - If a subsequent DNS query is made from the same UDP port, the response is correct as seen by tcpdump - When the response is seen by the application, the source IP address for the response is wrong I have inferred that as the response comes back from dnsip:53 and there is a connection table entry, IPVS seems to assume NAT is in use, and translates it using the entry (lvsip:50000 -> dnsip:53). The application layer then sees the response from (dnsvip:53), which is incorrect. /proc/version_signature (from both nodes): Ubuntu 3.13.0-100.147-generic 3.13.11-ckt39 Ubuntu 4.4.0-72.93~14.04.1-generic 4.4.49 IPVS Configuration: root@lvs5:~# ipvsadm -Sn -A -t 144.32.128.183:25 -s wlc -a -t 144.32.128.183:25 -r 144.32.129.29:25 -g -w 10 -a -t 144.32.128.183:25 -r 144.32.129.64:25 -g -w 10 -A -t 144.32.128.183:465 -s wlc -a -t 144.32.128.183:465 -r 144.32.129.29:465 -g -w 10 -a -t 144.32.128.183:465 -r 144.32.129.64:465 -g -w 10 -A -t 144.32.128.183:587 -s wlc -a -t 144.32.128.183:587 -r 144.32.129.29:587 -g -w 10 -a -t 144.32.128.183:587 -r 144.32.129.64:587 -g -w 10 -A -t 144.32.128.240:53 -s rr -a -t 144.32.128.240:53 -r 144.32.128.227:53 -g -w 10 -A -t 144.32.128.242:53 -s rr -a -t 144.32.128.242:53 -r 144.32.128.143:53 -g -w 10 -A -t 144.32.129.39:25 -s wlc -a -t 144.32.129.39:25 -r 144.32.129.163:25 -g -w 10 -a -t 144.32.129.39:25 -r 144.32.129.164:25 -g -w 10 -A -t 144.32.129.39:465 -s wlc -a -t 144.32.129.39:465 -r 144.32.129.163:465 -g -w 10 -a -t 144.32.129.39:465 -r 144.32.129.164:465 -g -w 10 -A -t 144.32.129.39:587 -s wlc -a -t 144.32.129.39:587 -r 144.32.129.163:587 -g -w 10 -a -t 144.32.129.39:587 -r 144.32.129.164:587 -g -w 10 -A -u 144.32.128.240:53 -s rr -a -u 144.32.128.240:53 -r 144.32.128.227:53 -g -w 10 -A -u 144.32.128.242:53 -s rr -a -u 144.32.128.242:53 -r 144.32.128.143:53 -g -w 10 --- AlsaDevices: total 0 crw-rw---- 1 root audio 116, 1 Apr 11 13:18 seq crw-rw---- 1 root audio 116, 33 Apr 11 13:18 timer AplayDevices: Error: [Errno 2] No such file or directory ApportVersion: 2.14.1-0ubuntu3.23 Architecture: amd64 ArecordDevices: Error: [Errno 2] No such file or directory AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1: CRDA: Error: [Errno 2] No such file or directory DistroRelease: Ubuntu 14.04 HibernationDevice: RESUME=/dev/mapper/lvs5--vg-swap IwConfig: Error: [Errno 2] No such file or directory Lsusb: Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 003: ID 413c:a001 Dell Computer Corp. Hub Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub MachineType: Dell Inc. PowerEdge R320 Package: linux (not installed) PciMultimedia: ProcFB: 0 VESA VGA ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-72-generic root=/dev/mapper/hostname--vg-root ro quiet splash vt.handoff=7 ProcVersionSignature: Ubuntu 4.4.0-72.93~14.04.1-generic 4.4.49 RelatedPackageVersions: linux-restricted-modules-4.4.0-72-generic N/A linux-backports-modules-4.4.0-72-generic N/A linux-firmware 1.127.23 RfKill: Error: [Errno 2] No such file or directory Tags: trusty Uname: Linux 4.4.0-72-generic x86_64 UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: btcats daemon dba named oinstall yimsora _MarkForUpload: True dmi.bios.date: 01/29/2015 dmi.bios.vendor: Dell Inc. dmi.bios.version: 2.4.2 dmi.board.name: 0KM5PX dmi.board.vendor: Dell Inc. dmi.board.version: A02 dmi.chassis.type: 23 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvr2.4.2:bd01/29/2015:svnDellInc.:pnPowerEdgeR320:pvr:rvnDellInc.:rn0KM5PX:rvrA02:cvnDellInc.:ct23:cvr: dmi.product.name: PowerEdge R320 dmi.sys.vendor: Dell Inc. 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