Android client SYN packets dropped

[Arto Huusko <armihu%gmail.com@localhost>]

Hello, I need help resolving a problem in my LAN.

My Android 10 phone is unable to connect to any TCP services hosted
on a NetBSD -current 9.99.73 server. Connections to the services
from other devices on the same LAN work.

My setup:

- NetBSD server connected to an Asus router via 1Gb ethernet
- Various wifi devices connected to the same Asus router
- Asus router bridges the wifi and ethernet networks

Here is what I have found:

The NetBSD server receives SYN packet from the Android device. And then
nothing happens.

Here is a working SYN, SYN-ACK pair from a wireless Linux laptop:

16:23:07.941446 IP 192.168.1.137.52091 > 192.168.1.2.http: Flags [S], 
seq 2002477302, win 64106, options [mss 9158,nop,wscale 
8,nop,nop,sackOK], length 0
16:23:07.941470 IP 192.168.1.2.http > 192.168.1.137.52091: Flags [S.], 
seq 1642340388, ack 2002477303, win 65535, options [mss 1460,nop,wscale 
3,sackOK,eol], length 0


And this is a SYN packet from the Android device:

16:05:08.452102 IP 192.168.1.133.45086 > 192.168.1.2.http: Flags [S], 
seq 3821589786, win 65535, options [mss 1460,sackOK,TS val 1473889759 
ecr 0,nop,wscale 12], length 0

The NetBSD server does not send any response.

Looking at netstat -s output, the dropped SYN packets are recorded here:

        90 SYNs dropped (no route or no space)

that increases every time I try to connect from the Android device.


How can I fix this?


Thanks,
Arto Huusko