Hi again, first of all: Thanks for fixing the last nsupdate bug so fast! Sadly I saw another issue with nsupdate. If I define the server to send the update to, *and* request ipv6 as transport protocol, I will get an INSIST in mem.c: $ { echo "server ns2.hznet.de."; echo "update del test.hznet.de IN TXT hello"; echo; } | nsupdate -d -6 -v mem.c:709: INSIST(*cp == 0xbe) failed, back trace #0 0x5a7b74 in ?? #1 0x5a7ada in ?? #2 0x40ff39 in ?? #3 0x5bb530 in ?? #4 0x413558 in ?? #5 0x41595d in ?? #6 0x5c819b in ?? #7 0x7f8966477184 in ?? #8 0x7f8965e3dffd in ?? Aborted (core dumped) This is the current version from the git repository: $ nsupdate -V nsupdate 9.12.0b1 Don't know this helps, but here is the stack trace: $ gdb /usr/local/bin/nsupdate core GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.3) 7.7.1 Copyright (C) 2014 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: . Find the GDB manual and other documentation resources online at: . For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from /usr/local/bin/nsupdate...done. [New LWP 2908] [New LWP 2905] [New LWP 2907] [New LWP 2906] [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". Core was generated by `nsupdate -d -6 -v'. Program terminated with signal SIGABRT, Aborted. #0 0x00007f8965d76c37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 56 ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory. (gdb) bt #0 0x00007f8965d76c37 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 #1 0x00007f8965d7a028 in __GI_abort () at abort.c:89 #2 0x00000000005a7adf in isc_assertion_failed (file=file@entry=0x621870 "mem.c", line=line@entry=709, type=type@entry=isc_assertiontype_insist, cond=cond@entry=0x621864 "*cp == 0xbe") at assertions.c:50 #3 0x000000000040ff39 in check_overrun (mem=mem@entry=0x7f8967380010, size=, size@entry=0, new_size=new_size@entry=8) at mem.c:709 #4 0x00000000005bb530 in mem_putunlocked (size=0, mem=0x7f8967380010, ctx=0x1441010) at mem.c:739 #5 isc___mem_put (ctx0=0x1441010, ptr=0x7f8967380010, size=0, file=0x5e39a4 "./nsupdate.c", line=) at mem.c:1337 #6 0x0000000000413558 in evaluate_server (cmdline=0x0) at ./nsupdate.c:1556 #7 do_next_command (cmdline=0x7f8963751dd7 "ns2.hznet.de.") at ./nsupdate.c:2175 #8 get_next_command () at ./nsupdate.c:2290 #9 0x000000000041595d in user_interaction () at ./nsupdate.c:2305 #10 getinput (task=, event=) at ./nsupdate.c:3329 #11 0x00000000005c819b in dispatch (manager=0x7f896738a010) at task.c:1137 #12 run (uap=0x7f896738a010) at task.c:1309 #13 0x00007f8966477184 in start_thread (arg=0x7f8963772700) at pthread_create.c:312 #14 0x00007f8965e3dffd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111 (gdb) quit Again, many thanks for your help BR Holger