send udp data fail

[quyong123]

hello:
I use cc2538 as 6lbr, and another cc2538 as udp-client run contiki udp-client.c demo.
then, udp-client send data to PC, and PC use spkit App receive data, data receive is normal.
but PC send data to uds-client have problem, send data size greater than six ,is fail. but send data size Not more than six, is success.

this is client-udp serial output data when PC send data is "1234567":

sicslowpan input: IPHC
IPHC: CID flag set - increase header with one
IPHC: next header inline: 0
Uncompressing 0 + 16 => ::FFFF:172.16.0.3
Uncompressing 8 + 0 => aaaa::212:4b00:5af:7eec
sicslowpan input: IP packet ready (length 63)
after decompression 23:600000000017003f00000000000000000000ffffac100003aaaa00000000000002124b0005af7eec11006304801e01000bb80bb9000f9d0031323334353637
IPv6 packet received from ::FFFF:172.16.0.3 to aaaa::212:4b00:5af:7eec
Processing RPL option
RPL: Packet going down, sender closer 1 (256 < 512)
RPL: Rank OK
Forwarding packet to aaaa::212:4b00:5af:7eec
Sending packet with length 63 (23)
RPL: Updating RPL option
uip-ds6-route: Looking up route for aaaa::212:4b00:5af:7eec
uip-ds6-route: No route found
RPL: Forwarding error
RPL: Generate No-Path DAO
RPL: Sending a No-Path DAO with sequence number 241, lifetime 0, prefix aaaa::212:4b00:5af:7eec to fe80::212:4b00:5af:7ebc , parent fe80::212:4b00:5af:7ebc
Upper layer checksum len: 50 from: 40
sicslowpan output: sending packet len 90
before compression (50): 6000000000323a40fe8000000000000002124b0005af7eecfe8000000000000002124b0005af7ebc9b024ec51e4000f1fd0000000000000002124b0005af7ebc05120080aaaa00000000000002124b0005af7eec060400000000
sicslowpan output: header of len 3
tcpip_ipv6_output: RPL header update error
RPL: rpl_link_neighbor_callback triggering update
RPL: rpl_process_parent_event recalculate_ranks