Problems after upgrade to 9.10.4

Michael Brunnbauer brunni at netestate.de
Thu May 5 07:31:06 UTC 2016 

hi all,

after upgrading from bind 9.10.3-P2 to 9.10.4, I have intermittent DNS lookup
errors on one of my servers with low DNS load. The server is not authoritative 
for the affected zones but the authoritative servers are under my control and
show no problems. So far, I have not been able to reproduce this on other 
servers with 9.10.4.

I have intercepted one of the failing DNS looups (A-record for
ts.foaf-search.net) leading to an error with tcpdump. The A-record is received
4 seconds after the initial query to e.gtld-servers.net, which may be too late
for the standard timeout of 5 seconds. A second attempt should have been 
started by the DNS client in this case but the lookup attempted at this time
failed.

Can anybody see what is going wrong here?

07:25:08.157974 IP (tos 0x0, ttl 64, id 22351, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.40611 > 192.12.94.30.53: [bad udp cksum 0x21e0 -> 0xcab7!] 48603 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:08.158034 IP (tos 0x0, ttl 64, id 22352, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.63722 > 192.12.94.30.53: [bad udp cksum 0x21e0 -> 0xd69b!] 22421 [1au] AAAA? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:08.184440 IP (tos 0x0, ttl 56, id 516, offset 0, flags [none], proto UDP (17), length 444)
    192.12.94.30.53 > 81.209.177.155.40611: [udp sum ok] 48603-| q: A? ts.foaf-search.net. 0/5/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50 ar: . OPT UDPsize=4096 OK (416)
07:25:08.184603 IP (tos 0x0, ttl 64, id 36699, offset 0, flags [DF], proto TCP (6), length 60)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [S], cksum 0x21c6 (incorrect -> 0x051c), seq 2024571414, win 14600, options [mss 1460,sackOK,TS val 65473869 ecr 0,nop,wscale 7], length 0
07:25:08.192301 IP (tos 0x0, ttl 52, id 62211, offset 0, flags [none], proto UDP (17), length 444)
    192.12.94.30.53 > 81.209.177.155.63722: [udp sum ok] 22421-| q: AAAA? ts.foaf-search.net. 0/5/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50 ar: . OPT UDPsize=4096 OK (416)
07:25:08.192391 IP (tos 0x0, ttl 64, id 6794, offset 0, flags [DF], proto TCP (6), length 60)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [S], cksum 0x21c6 (incorrect -> 0x8269), seq 1533614047, win 14600, options [mss 1460,sackOK,TS val 65473877 ecr 0,nop,wscale 7], length 0
07:25:08.218583 IP (tos 0x0, ttl 52, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    192.12.94.30.53 > 81.209.177.155.56344: Flags [S.], cksum 0x806c (correct), seq 3355374206, ack 2024571415, win 14480, options [mss 1460,sackOK,TS val 2381790369 ecr 65473869,nop,wscale 7], length 0
07:25:08.218599 IP (tos 0x0, ttl 64, id 36700, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0xe733), seq 1, ack 1, win 115, options [nop,nop,TS val 65473903 ecr 2381790369], length 0
07:25:08.218675 IP (tos 0x0, ttl 64, id 36701, offset 0, flags [DF], proto TCP (6), length 101)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [P.], cksum 0x21ef (incorrect -> 0xfbf3), seq 1:50, ack 1, win 115, options [nop,nop,TS val 65473903 ecr 2381790369], length 4913389 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:08.226633 IP (tos 0x0, ttl 52, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    192.12.94.30.53 > 81.209.177.155.58941: Flags [S.], cksum 0x2d5b (correct), seq 2873024405, ack 1533614048, win 14480, options [mss 1460,sackOK,TS val 2381790377 ecr 65473877,nop,wscale 7], length 0
07:25:08.226647 IP (tos 0x0, ttl 64, id 6795, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0x9422), seq 1, ack 1, win 115, options [nop,nop,TS val 65473911 ecr 2381790377], length 0
07:25:08.226693 IP (tos 0x0, ttl 64, id 6796, offset 0, flags [DF], proto TCP (6), length 101)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [P.], cksum 0x21ef (incorrect -> 0x351e), seq 1:50, ack 1, win 115, options [nop,nop,TS val 65473911 ecr 2381790377], length 4942998 [1au] AAAA? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:08.252651 IP (tos 0x0, ttl 52, id 52924, offset 0, flags [DF], proto TCP (6), length 52)
    192.12.94.30.53 > 81.209.177.155.56344: Flags [.], cksum 0xe6e1 (correct), seq 1, ack 50, win 114, options [nop,nop,TS val 2381790403 ecr 65473903], length 0
07:25:08.253543 IP (tos 0x0, ttl 52, id 52925, offset 0, flags [DF], proto TCP (6), length 633)
    192.12.94.30.53 > 81.209.177.155.56344: Flags [P.], cksum 0xcd5c (correct), seq 1:582, ack 50, win 114, options [nop,nop,TS val 2381790404 ecr 65473903], length 58113389- q: A? ts.foaf-search.net. 0/6/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] RRSIG ar: . OPT UDPsize=4096 OK (579)
07:25:08.253554 IP (tos 0x0, ttl 64, id 36702, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0xe46e), seq 50, ack 582, win 124, options [nop,nop,TS val 65473938 ecr 2381790404], length 0
07:25:08.253738 IP (tos 0x0, ttl 64, id 36703, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [F.], cksum 0x21be (incorrect -> 0xe46d), seq 50, ack 582, win 124, options [nop,nop,TS val 65473938 ecr 2381790404], length 0
07:25:08.260980 IP (tos 0x0, ttl 52, id 58205, offset 0, flags [DF], proto TCP (6), length 52)
    192.12.94.30.53 > 81.209.177.155.58941: Flags [.], cksum 0x93d0 (correct), seq 1, ack 50, win 114, options [nop,nop,TS val 2381790411 ecr 65473911], length 0
07:25:08.261499 IP (tos 0x0, ttl 52, id 58206, offset 0, flags [DF], proto TCP (6), length 633)
    192.12.94.30.53 > 81.209.177.155.58941: Flags [P.], cksum 0x0687 (correct), seq 1:582, ack 50, win 114, options [nop,nop,TS val 2381790412 ecr 65473911], length 58142998- q: AAAA? ts.foaf-search.net. 0/6/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] RRSIG ar: . OPT UDPsize=4096 OK (579)
07:25:08.261506 IP (tos 0x0, ttl 64, id 6797, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0x915d), seq 50, ack 582, win 124, options [nop,nop,TS val 65473946 ecr 2381790412], length 0
07:25:08.261618 IP (tos 0x0, ttl 64, id 6798, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [F.], cksum 0x21be (incorrect -> 0x915c), seq 50, ack 582, win 124, options [nop,nop,TS val 65473946 ecr 2381790412], length 0
07:25:08.261855 IP (tos 0x0, ttl 64, id 3186, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.52664 > 192.33.14.30.53: [bad udp cksum 0xd1f4 -> 0x65ed!] 17276 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:08.261910 IP (tos 0x0, ttl 64, id 3187, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.13575 > 192.33.14.30.53: [bad udp cksum 0xd1f4 -> 0x8d5d!] 46242 [1au] AAAA? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:08.287759 IP (tos 0x0, ttl 52, id 52926, offset 0, flags [DF], proto TCP (6), length 52)
    192.12.94.30.53 > 81.209.177.155.56344: Flags [F.], cksum 0xe454 (correct), seq 582, ack 51, win 114, options [nop,nop,TS val 2381790438 ecr 65473938], length 0
07:25:08.287776 IP (tos 0x0, ttl 64, id 36704, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.56344 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0xe428), seq 51, ack 583, win 124, options [nop,nop,TS val 65473972 ecr 2381790438], length 0
07:25:08.291247 IP (tos 0x0, ttl 58, id 22534, offset 0, flags [none], proto UDP (17), length 444)
    192.33.14.30.53 > 81.209.177.155.52664: [no cksum] 17276-| q: A? ts.foaf-search.net. 0/5/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50 ar: . OPT UDPsize=4096 OK (416)
07:25:08.291397 IP (tos 0x0, ttl 64, id 49775, offset 0, flags [DF], proto TCP (6), length 60)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [S], cksum 0xd1da (incorrect -> 0x4fcf), seq 1195298775, win 14600, options [mss 1460,sackOK,TS val 65473976 ecr 0,nop,wscale 7], length 0
07:25:08.294368 IP (tos 0x0, ttl 58, id 34785, offset 0, flags [none], proto UDP (17), length 444)
    192.33.14.30.53 > 81.209.177.155.13575: [no cksum] 46242-| q: AAAA? ts.foaf-search.net. 0/5/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50 ar: . OPT UDPsize=4096 OK (416)
07:25:08.294450 IP (tos 0x0, ttl 64, id 19332, offset 0, flags [DF], proto TCP (6), length 60)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [S], cksum 0xd1da (incorrect -> 0x8d93), seq 3005040191, win 14600, options [mss 1460,sackOK,TS val 65473979 ecr 0,nop,wscale 7], length 0
07:25:08.295903 IP (tos 0x0, ttl 52, id 58207, offset 0, flags [DF], proto TCP (6), length 52)
    192.12.94.30.53 > 81.209.177.155.58941: Flags [F.], cksum 0x9143 (correct), seq 582, ack 51, win 114, options [nop,nop,TS val 2381790446 ecr 65473946], length 0
07:25:08.295912 IP (tos 0x0, ttl 64, id 6799, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.58941 > 192.12.94.30.53: Flags [.], cksum 0x21be (incorrect -> 0x9117), seq 51, ack 583, win 124, options [nop,nop,TS val 65473980 ecr 2381790446], length 0
07:25:08.323722 IP (tos 0x0, ttl 58, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    192.33.14.30.53 > 81.209.177.155.50322: Flags [S.], cksum 0x2926 (correct), seq 1951254780, ack 1195298776, win 14480, options [mss 1460,sackOK,TS val 636142555 ecr 65473976,nop,wscale 7], length 0
07:25:08.323742 IP (tos 0x0, ttl 64, id 49776, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8fef), seq 1, ack 1, win 115, options [nop,nop,TS val 65474008 ecr 636142555], length 0
07:25:08.323822 IP (tos 0x0, ttl 64, id 49777, offset 0, flags [DF], proto TCP (6), length 101)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [P.], cksum 0xd203 (incorrect -> 0x5416), seq 1:50, ack 1, win 115, options [nop,nop,TS val 65474008 ecr 636142555], length 4934022 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:08.326703 IP (tos 0x0, ttl 58, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    192.33.14.30.53 > 81.209.177.155.42116: Flags [S.], cksum 0x27c8 (correct), seq 2125200829, ack 3005040192, win 14480, options [mss 1460,sackOK,TS val 636142558 ecr 65473979,nop,wscale 7], length 0
07:25:08.326716 IP (tos 0x0, ttl 64, id 19333, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8e91), seq 1, ack 1, win 115, options [nop,nop,TS val 65474011 ecr 636142558], length 0
07:25:08.326759 IP (tos 0x0, ttl 64, id 19334, offset 0, flags [DF], proto TCP (6), length 101)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [P.], cksum 0xd203 (incorrect -> 0x8fa6), seq 1:50, ack 1, win 115, options [nop,nop,TS val 65474011 ecr 636142558], length 4918397 [1au] AAAA? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:08.356161 IP (tos 0x0, ttl 58, id 2822, offset 0, flags [DF], proto TCP (6), length 52)
    192.33.14.30.53 > 81.209.177.155.50322: Flags [.], cksum 0x8f9f (correct), seq 1, ack 50, win 114, options [nop,nop,TS val 636142587 ecr 65474008], length 0
07:25:08.356302 IP (tos 0x0, ttl 58, id 2823, offset 0, flags [DF], proto TCP (6), length 633)
    192.33.14.30.53 > 81.209.177.155.50322: Flags [P.], cksum 0x2582 (correct), seq 1:582, ack 50, win 114, options [nop,nop,TS val 636142587 ecr 65474008], length 58134022- q: A? ts.foaf-search.net. 0/6/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] RRSIG ar: . OPT UDPsize=4096 OK (579)
07:25:08.356314 IP (tos 0x0, ttl 64, id 49778, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8d2f), seq 50, ack 582, win 124, options [nop,nop,TS val 65474041 ecr 636142587], length 0
07:25:08.356498 IP (tos 0x0, ttl 64, id 49779, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [F.], cksum 0xd1d2 (incorrect -> 0x8d2e), seq 50, ack 582, win 124, options [nop,nop,TS val 65474041 ecr 636142587], length 0
07:25:08.359064 IP (tos 0x0, ttl 58, id 15936, offset 0, flags [DF], proto TCP (6), length 52)
    192.33.14.30.53 > 81.209.177.155.42116: Flags [.], cksum 0x8e41 (correct), seq 1, ack 50, win 114, options [nop,nop,TS val 636142590 ecr 65474011], length 0
07:25:08.359379 IP (tos 0x0, ttl 58, id 15937, offset 0, flags [DF], proto TCP (6), length 633)
    192.33.14.30.53 > 81.209.177.155.42116: Flags [P.], cksum 0x6111 (correct), seq 1:582, ack 50, win 114, options [nop,nop,TS val 636142591 ecr 65474011], length 58118397- q: AAAA? ts.foaf-search.net. 0/6/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] RRSIG ar: . OPT UDPsize=4096 OK (579)
07:25:08.359389 IP (tos 0x0, ttl 64, id 19335, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8bd0), seq 50, ack 582, win 124, options [nop,nop,TS val 65474044 ecr 636142591], length 0
07:25:08.359498 IP (tos 0x0, ttl 64, id 19336, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [F.], cksum 0xd1d2 (incorrect -> 0x8bcf), seq 50, ack 582, win 124, options [nop,nop,TS val 65474044 ecr 636142591], length 0
07:25:08.359752 IP (tos 0x0, ttl 64, id 13080, offset 0, flags [none], proto UDP (17), length 88)
    81.209.177.155.32288 > 81.209.177.2.53: [bad udp cksum 0x0696 -> 0x189b!] 53230 [1au] A? ts.foaf-search.net.netestate.de. ar: . OPT UDPsize=512 OK (60)
07:25:08.359796 IP (tos 0x0, ttl 64, id 13081, offset 0, flags [none], proto UDP (17), length 88)
    81.209.177.155.29412 > 81.209.177.2.53: [bad udp cksum 0x0696 -> 0xdbd4!] 64752 [1au] AAAA? ts.foaf-search.net.netestate.de. ar: . OPT UDPsize=512 OK (60)
07:25:08.360022 IP (tos 0x0, ttl 64, id 29132, offset 0, flags [none], proto UDP (17), length 135)
    81.209.177.2.53 > 81.209.177.155.32288: [udp sum ok] 53230 NXDomain* q: A? ts.foaf-search.net.netestate.de. 0/1/1 ns: netestate.de. [10m] SOA ns1.netestate.de. brunni.netestate.de. 2016042901 14400 3600 864000 600 ar: . OPT UDPsize=4096 OK (107)
07:25:08.360066 IP (tos 0x0, ttl 64, id 29133, offset 0, flags [none], proto UDP (17), length 135)
    81.209.177.2.53 > 81.209.177.155.29412: [udp sum ok] 64752 NXDomain* q: AAAA? ts.foaf-search.net.netestate.de. 0/1/1 ns: netestate.de. [10m] SOA ns1.netestate.de. brunni.netestate.de. 2016042901 14400 3600 864000 600 ar: . OPT UDPsize=4096 OK (107)
07:25:08.388840 IP (tos 0x0, ttl 58, id 2824, offset 0, flags [DF], proto TCP (6), length 52)
    192.33.14.30.53 > 81.209.177.155.50322: Flags [F.], cksum 0x8d16 (correct), seq 582, ack 51, win 114, options [nop,nop,TS val 636142620 ecr 65474041], length 0
07:25:08.388856 IP (tos 0x0, ttl 64, id 49780, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.50322 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8cec), seq 51, ack 583, win 124, options [nop,nop,TS val 65474073 ecr 636142620], length 0
07:25:08.391833 IP (tos 0x0, ttl 58, id 15938, offset 0, flags [DF], proto TCP (6), length 52)
    192.33.14.30.53 > 81.209.177.155.42116: Flags [F.], cksum 0x8bb8 (correct), seq 582, ack 51, win 114, options [nop,nop,TS val 636142623 ecr 65474044], length 0
07:25:08.391850 IP (tos 0x0, ttl 64, id 19337, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42116 > 192.33.14.30.53: Flags [.], cksum 0xd1d2 (incorrect -> 0x8b8e), seq 51, ack 583, win 124, options [nop,nop,TS val 65474076 ecr 636142623], length 0
07:25:11.902216 IP (tos 0x0, ttl 64, id 23562, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.19477 > 192.26.92.30.53: [bad udp cksum 0x1fee -> 0xd4b6!] 2141 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:11.996783 IP (tos 0x0, ttl 55, id 40198, offset 0, flags [none], proto UDP (17), length 444)
    192.26.92.30.53 > 81.209.177.155.19477: [udp sum ok] 2141-| q: A? ts.foaf-search.net. 0/5/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50 ar: . OPT UDPsize=4096 OK (416)
07:25:11.996980 IP (tos 0x0, ttl 64, id 50216, offset 0, flags [DF], proto TCP (6), length 60)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [S], cksum 0x1fd4 (incorrect -> 0x7ed5), seq 3528841241, win 14600, options [mss 1460,sackOK,TS val 65477681 ecr 0,nop,wscale 7], length 0
07:25:12.091548 IP (tos 0x0, ttl 55, id 29174, offset 0, flags [DF], proto TCP (6), length 60)
    192.26.92.30.53 > 81.209.177.155.42432: Flags [S.], cksum 0x86e5 (correct), seq 1077272250, ack 3528841242, win 65535, options [mss 1460,nop,wscale 7,sackOK,TS val 1852416909 ecr 65477681], length 0
07:25:12.091577 IP (tos 0x0, ttl 64, id 50217, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [.], cksum 0x1fcc (incorrect -> 0xb4df), seq 1, ack 1, win 115, options [nop,nop,TS val 65477776 ecr 1852416909], length 0
07:25:12.091676 IP (tos 0x0, ttl 64, id 50218, offset 0, flags [DF], proto TCP (6), length 101)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [P.], cksum 0x1ffd (incorrect -> 0x732d), seq 1:50, ack 1, win 115, options [nop,nop,TS val 65477776 ecr 1852416909], length 4935519 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:12.187089 IP (tos 0x0, ttl 55, id 29264, offset 0, flags [DF], proto TCP (6), length 633)
    192.26.92.30.53 > 81.209.177.155.42432: Flags [P.], cksum 0x42c4 (correct), seq 1:582, ack 50, win 520, options [nop,nop,TS val 1852417004 ecr 65477776], length 58135519- q: A? ts.foaf-search.net. 0/6/1 ns: foaf-search.net. [2d] NS ns.netestate.de., foaf-search.net. [2d] NS ns1.netestate.de., A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] Type50, A1RT98BS5QGC9NFI51S9HCI47ULJG6JH.net. [1d] RRSIG, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] Type50, MI79E5R1F40QCUPOIBCU93AR486VI70V.net. [1d] RRSIG ar: . OPT UDPsize=4096 OK (579)
07:25:12.187127 IP (tos 0x0, ttl 64, id 50219, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [.], cksum 0x1fcc (incorrect -> 0xb1a1), seq 50, ack 582, win 124, options [nop,nop,TS val 65477872 ecr 1852417004], length 0
07:25:12.187431 IP (tos 0x0, ttl 64, id 35364, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.40369 > 81.26.171.34.53: [bad udp cksum 0xfff1 -> 0xfb92!] 45024 [1au] A? ts.foaf-search.net. ar: . OPT UDPsize=512 OK (47)
07:25:12.187457 IP (tos 0x0, ttl 64, id 50220, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [F.], cksum 0x1fcc (incorrect -> 0xb1a0), seq 50, ack 582, win 124, options [nop,nop,TS val 65477872 ecr 1852417004], length 0
07:25:12.196394 IP (tos 0x0, ttl 54, id 59318, offset 0, flags [none], proto UDP (17), length 91)
    81.26.171.34.53 > 81.209.177.155.40369: [udp sum ok] 45024* q: A? ts.foaf-search.net. 1/0/1 ts.foaf-search.net. [10m] A 81.209.177.155 ar: . OPT UDPsize=4096 OK (63)
07:25:12.197024 IP (tos 0x0, ttl 64, id 13804, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.46017 > 81.209.177.2.53: [bad udp cksum 0x0689 -> 0xc140!] 52578 [1au] AAAA? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:12.197374 IP (tos 0xd4, ttl 64, id 29405, offset 0, flags [none], proto UDP (17), length 134)
    81.209.177.2.53 > 81.209.177.155.46017: [udp sum ok] 52578* q: AAAA? ts.foaf-search.net. 0/1/1 ns: foaf-search.net. [10m] SOA ns1.netestate.de. brunni.netestate.de. 2013110601 14400 3600 864000 600 ar: . OPT UDPsize=4096 OK (106)
07:25:12.197723 IP (tos 0x0, ttl 64, id 13805, offset 0, flags [none], proto UDP (17), length 75)
    81.209.177.155.60373 > 81.209.177.2.53: [bad udp cksum 0x0689 -> 0xaadb!] 43968 [1au] MX? ts.foaf-search.net. ar: . OPT UDPsize=4096 OK (47)
07:25:12.198047 IP (tos 0xd4, ttl 64, id 29406, offset 0, flags [none], proto UDP (17), length 134)
    81.209.177.2.53 > 81.209.177.155.60373: [udp sum ok] 43968* q: MX? ts.foaf-search.net. 0/1/1 ns: foaf-search.net. [10m] SOA ns1.netestate.de. brunni.netestate.de. 2013110601 14400 3600 864000 600 ar: . OPT UDPsize=4096 OK (106)
07:25:12.282129 IP (tos 0x0, ttl 55, id 29382, offset 0, flags [DF], proto TCP (6), length 52)
    192.26.92.30.53 > 81.209.177.155.42432: Flags [.], cksum 0xafb5 (correct), seq 582, ack 51, win 520, options [nop,nop,TS val 1852417099 ecr 65477872], length 0
07:25:12.282166 IP (tos 0x0, ttl 55, id 29383, offset 0, flags [DF], proto TCP (6), length 52)
    192.26.92.30.53 > 81.209.177.155.42432: Flags [F.], cksum 0xafb4 (correct), seq 582, ack 51, win 520, options [nop,nop,TS val 1852417099 ecr 65477872], length 0
07:25:12.282181 IP (tos 0x0, ttl 64, id 46003, offset 0, flags [DF], proto TCP (6), length 52)
    81.209.177.155.42432 > 192.26.92.30.53: Flags [.], cksum 0xb0e1 (correct), seq 51, ack 583, win 124, options [nop,nop,TS val 65477967 ecr 1852417099], length 0

The error counters on /proc/net/udp are all zero and I see no warnings from
bind in the syslog. I use glibc-2.23 and have no special options configured:

options {
        directory "/etc/named";
        allow-query {
        127.0.0.1;
        };
};

zone "." {
        type hint;
        file "named.ca";
};

zone "0.0.127.in-addr.arpa" {
        type master;
        file "0.0.127.in-addr.arpa";
        notify no;
};


May  4 16:28:37 chianti named[3352]: starting BIND 9.10.4 <id:a5e4938> -t /etc/namedroot -u named
May  4 16:28:37 chianti named[3352]: running on Linux x86_64 3.4.112 #4 SMP Tue May 3 13:08:00 CEST 2016
May  4 16:28:37 chianti named[3352]: built with '--prefix=/usr' '--with-openssl=/usr/lib/ssl' '--enable-threads'
May  4 16:28:37 chianti named[3352]: ----------------------------------------------------
May  4 16:28:37 chianti named[3352]: BIND 9 is maintained by Internet Systems Consortium,
May  4 16:28:37 chianti named[3352]: Inc. (ISC), a non-profit 501(c)(3) public-benefit
May  4 16:28:37 chianti named[3352]: corporation.  Support and training for BIND 9 are
May  4 16:28:37 chianti named[3352]: available at https://www.isc.org/support
May  4 16:28:37 chianti named[3352]: ----------------------------------------------------
May  4 16:28:37 chianti named[3352]: adjusted limit on open files from 65536 to 1048576
May  4 16:28:37 chianti named[3352]: found 2 CPUs, using 2 worker threads
May  4 16:28:37 chianti named[3352]: using 1 UDP listener per interface
May  4 16:28:37 chianti named[3352]: using up to 4096 sockets
May  4 16:28:37 chianti named[3352]: loading configuration from '/usr/etc/named.conf'
May  4 16:28:37 chianti named[3352]: using default UDP/IPv4 port range: [1024, 65535]
May  4 16:28:37 chianti named[3352]: using default UDP/IPv6 port range: [1024, 65535]
May  4 16:28:37 chianti named[3352]: no IPv6 interfaces found
May  4 16:28:37 chianti named[3352]: listening on IPv4 interface lo, 127.0.0.1#53
May  4 16:28:37 chianti named[3352]: listening on IPv4 interface eth0, 81.209.177.155#53
May  4 16:28:37 chianti named[3352]: generating session key for dynamic DNS
May  4 16:28:37 chianti named[3352]: sizing zone task pool based on 2 zones
May  4 16:28:37 chianti named[3352]: set up managed keys zone for view _default, file 'managed-keys.bind'
May  4 16:28:37 chianti named[3352]: automatic empty zone: 10.IN-ADDR.ARPA
[...]

/etc/resolv.conf:
domain netestate.de
nameserver 127.0.0.1

Maybe the short TTL of 10 minutes for my zones is aggravating this problem.
I guess I should at least increase the TTL for the NS records when this
problem is solved?

thnx,
cu,
brunni

-- 
++  Michael Brunnbauer
++  netEstate GmbH
++  Geisenhausener Straße 11a
++  81379 München
++  Tel +49 89 32 19 77 80
++  Fax +49 89 32 19 77 89 
++  E-Mail brunni at netestate.de
++  http://www.netestate.de/
++
++  Sitz: München, HRB Nr.142452 (Handelsregister B München)
++  USt-IdNr. DE221033342
++  Geschäftsführer: Michael Brunnbauer, Franz Brunnbauer
++  Prokurist: Dipl. Kfm. (Univ.) Markus Hendel
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