[lwip-users] PPP TCP Connect: "max SYN retries reached"

[mjackson]

Hi Everyone,

As you can see from time-stamp(ts) [23:58:28.420], PPP has successfully
negotiated with the cellular network.  I run into problems when I try to
make a TCP connection to a remote server using netconn_connect.  Initially,
LWIP sends the 'SYN' flag to the sever as it should, see ts[23:58:31.210 ]. 
Then LWIP sends the SYN flag an additional 4 times before it errors out for
"max SYN retries reached", see ts[23:58:40.726 ]

However right after this, the server finally respond with the appropriate
ACK/SYN, see ts[23:58:40.957 ].  Unfortunately the PCB was previously purged
"tcp_pcb_purge" at ts[23:58:40.726 ], which ultimately causes LWIP to
respond with ACK/RST.

Even if I change max SYN retries to 12, I get the exact same behavior.

Any insight into my problem will be greatly appreciated.



Log as Followed:
Time-Stamp(ts)
[23:58:28.420 ] rcvd [IPCP ConfAck id=0x7 <addr 32.178.195.248> <ms-dns1
209.183.33.23> <ms-dns2 209.183.35.23>]
[23:58:28.420 ] ipcp: up
[23:58:28.420 ] Could not determine remote IP address: defaulting to 0.0.0.0
[23:58:28.420 ] sifvjcomp: VJ compress enable=0 slot=0 max slot=0
[23:58:28.420 ] sifup: unit 0: err_code=0
[23:58:28.420 ] local  IP address 32.178.195.248
[23:58:28.420 ] primary   DNS address 209.183.33.23
[23:58:28.420 ] secondary DNS address 209.183.35.23
[23:58:28.420 ] ppp phase changed: unit 0: phase=8
[23:58:28.453 ] tcp_bind: bind to port 49153
[23:58:28.453 ] tcp_connect to port 80
[23:58:28.453 ] ppp_netif_output[0]: proto=0x21
[23:58:28.453 ]   0000: 7E 21 45 00 00 2C 00 02 00 00 FF 06 DA 36 20 B2
[23:58:28.453 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6D 00 00
[23:58:28.453 ]   0020: 00 00 60 02 05 DC D6 F8 00 00 02 04 05 B4 5D 54
[23:58:28.453 ]   0030: 7E
[23:58:28.453 ] 
[23:58:28.677 ] tcp_slowtmr: processing active pcb
[23:58:29.188 ] tcp_slowtmr: processing active pcb
[23:58:29.683 ] tcp_slowtmr: processing active pcb
[23:58:30.193 ] tcp_slowtmr: processing active pcb
[23:58:30.193 ] tcp_slowtmr: polling application
[23:58:30.687 ] tcp_slowtmr: processing active pcb
[23:58:31.210 ] tcp_slowtmr: processing active pcb
[23:58:31.210 ] ppp_netif_output[0]: proto=0x21
[23:58:31.210 ]   0000: 7E 21 45 00 00 2C 00 03 00 00 FF 06 DA 35 20 B2
[23:58:31.210 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6D 00 00
[23:58:31.210 ]   0020: 00 00 60 02 05 DC D6 F8 00 00 02 04 05 B4 A1 5A
[23:58:31.210 ]   0030: 7E
[23:58:31.210 ] 
[23:58:31.690 ] tcp_slowtmr: processing active pcb
[23:58:32.200 ] tcp_slowtmr: processing active pcb
[23:58:32.200 ] tcp_slowtmr: polling application
[23:58:32.694 ] tcp_slowtmr: processing active pcb
[23:58:33.189 ] tcp_slowtmr: processing active pcb
[23:58:33.685 ] tcp_slowtmr: processing active pcb
[23:58:34.179 ] tcp_slowtmr: processing active pcb
[23:58:34.220 ] ppp_netif_output[0]: proto=0x21
[23:58:34.220 ]   0000: 7E 21 45 00 00 2C 00 04 00 00 FF 06 DA 34 20 B2
[23:58:34.220 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6D 00 00
[23:58:34.220 ]   0020: 00 00 60 02 05 DC D6 F8 00 00 02 04 05 B4 12 12
[23:58:34.220 ]   0030: 7E
[23:58:34.220 ] 
[23:58:34.220 ] tcp_slowtmr: polling application
[23:58:34.697 ] tcp_slowtmr: processing active pcb
[23:58:35.193 ] tcp_slowtmr: processing active pcb
[23:58:35.686 ] tcp_slowtmr: processing active pcb
[23:58:36.207 ] tcp_slowtmr: processing active pcb
[23:58:36.207 ] tcp_slowtmr: polling application
[23:58:36.702 ] tcp_slowtmr: processing active pcb
[23:58:37.226 ] tcp_slowtmr: processing active pcb
[23:58:37.226 ] ppp_netif_output[0]: proto=0x21
[23:58:37.226 ]   0000: 7E 21 45 00 00 2C 00 05 00 00 FF 06 DA 33 20 B2
[23:58:37.226 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6D 00 00
[23:58:37.226 ]   0020: 00 00 60 02 05 DC D6 F8 00 00 02 04 05 B4 AA BA
[23:58:37.226 ]   0030: 7E
[23:58:37.226 ] 
[23:58:37.704 ] tcp_slowtmr: processing active pcb
[23:58:38.213 ] tcp_slowtmr: processing active pcb
[23:58:38.213 ] tcp_slowtmr: polling application
[23:58:38.710 ] tcp_slowtmr: processing active pcb
[23:58:39.205 ] tcp_slowtmr: processing active pcb
[23:58:39.697 ] tcp_slowtmr: processing active pcb
[23:58:40.193 ] tcp_slowtmr: processing active pcb
[23:58:40.233 ] ppp_netif_output[0]: proto=0x21
[23:58:40.233 ]   0000: 7E 21 45 00 00 2C 00 06 00 00 FF 06 DA 32 20 B2
[23:58:40.233 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6D 00 00
[23:58:40.233 ]   0020: 00 00 60 02 05 DC D6 F8 00 00 02 04 05 B4 F2 48
[23:58:40.233 ]   0030: 7E
[23:58:40.233 ] 
[23:58:40.233 ] tcp_slowtmr: polling application
[23:58:40.726 ] tcp_slowtmr: processing active pcb
[23:58:40.726 ] tcp_slowtmr: max SYN retries reached
[23:58:40.726 ] tcp_pcb_purge
[23:58:40.726 ] tcp_pcb_purge: data left on ->unacked
[23:58:40.957 ] pppos_input[0]: got 49 bytes
[23:58:40.957 ]   0000: 7E 21 45 00 00 2C 2A 48 40 00 69 06 05 F1 17 17
[23:58:40.957 ]   0010: E5 D1 20 B2 C3 F8 00 50 C0 01 00 AA 9B 28 00 00
[23:58:40.957 ]   0020: 19 6E 60 12 20 00 21 55 00 00 02 04 05 50 45 53
[23:58:40.957 ]   0030: 7E
[23:58:40.957 ] 
[23:58:40.957 ] ppp_input[0]: ip in pbuf len=44
[23:58:40.957 ] 
[23:58:40.957 ] +-+-+-+-+-+-+-+-+-+-+-+-+-+- 
[23:58:40.957 ] tcp_input: flags SYN ACK 
[23:58:40.957 ] -+-+-+-+-+-+-+-+-+-+-+-+-+-+
[23:58:40.957 ] 
[23:58:40.957 ] tcp_input: no PCB match found, resetting.
[23:58:40.957 ] ppp_netif_output[0]: proto=0x21
[23:58:40.957 ]   0000: 7E 21 45 00 00 28 00 07 00 00 FF 06 DA 35 20 B2
[23:58:40.957 ]   0010: C3 F8 17 17 E5 D1 C0 01 00 50 00 00 19 6E 00 AA
[23:58:40.957 ]   0020: 9B 29 50 14 05 DC 52 CE 00 00 1F 2D 7E

Maurice



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