Hello Bill,
I've got the same issue. It's just because your linux system supports dualstack sockets by default, but wakaama's connection tracker doesn't. Just define server host exactly, when you call lwm2mclient
[vtrushkin@TARDIS build]$ sudo tcpdump -ni any -T coap udp port 5683
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
### $ ./lwm2mclient
13:20:15.750184 IP 127.0.0.1.56830 > 127.0.0.1.5683: CoAP<0x1a26[CON]> 0x261ad906 0.02 POST: Uri-Path=rd Uri-Query=ep=testlwm2mclient Uri-Query=b=U Uri-Query=lt=300 [Payload 82 bytes]
13:20:15.750525 IP 127.0.0.1.5683 > 127.0.0.1.56830: CoAP<0x1a26[ACK]> 0x261ad906 2.01 Created: Location-Path=rd Location-Path=0
13:20:21.757089 IP 127.0.0.1.56830 > 127.0.0.1.5683: CoAP<0x1a26[CON]> 0x261ad906 0.02 POST: Uri-Path=rd Uri-Query=ep=testlwm2mclient Uri-Query=b=U Uri-Query=lt=300 [Payload 82 bytes]
13:20:21.757489 IP 127.0.0.1.5683 > 127.0.0.1.56830: CoAP<0x1a26[ACK]> 0x261ad906 2.01 Created: Location-Path=rd Location-Path=0
### $ ./lwm2mclient -h ::1
13:20:39.055472 IP6 ::1.56830 > ::1.5683: CoAP<0x08cd[CON]> 0xcd08f706 0.02 POST: Uri-Path=rd Uri-Query=ep=testlwm2mclient Uri-Query=b=U Uri-Query=lt=300 [Payload 82 bytes]
13:20:39.055686 IP6 ::1.5683 > ::1.56830: CoAP<0x08cd[ACK]> 0xcd08f706 2.01 Created: Location-Path=rd Location-Path=0
Best,
Vyacheslav
