[Wien] strange RSTs over IPv4

[Gui Iribarren]

today, since i woke up "internet was not working" at stein712
i just time to take a closer look, and something funny is going on.
global ipv6 works as expected.
ipv4 icmps also work fine, RTT to various known places is legit
but any tcpv4 fails misteriously with a RST
a tcpdump on both ends (laptop inside funkfeuer and a server outside of austria) shows the syn, syn/ack, ack handshake go without problem, but then the first data packet server->laptop never reaches the laptop, instead the server receives a RST around 50ms after (roughly the RTT laptop-server, which would indicate the RST comes from near the laptop i.e. funkfeuer or austria at least)

this misterious RST is *not* coming from my laptop.

the first data packet laptop-server *does* reach the server. server replies with a RST, since it already dropped the connection.

just in case, i reproduced the same behaviour using starting point my openwrt node (so, one hop upstream from my laptop) which is as far as i have admin access. previous paragraphs apply s/laptop/ubiquiti/g

any ideas?