gPXE responds to duplicated ACKs with an immediate retransmission,
which can lead to a sorceror's apprentice syndrome. It also responds
to out-of-range (or old duplicate) ACKs with a RST, which can cause
valid connections to be dropped.
Fix the sorceror's apprentice syndrome by leaving the retransmission
timer running (and so inhibiting the immediate retransmission) when we
receive a potential duplicate ACK. This seems to match the behaviour
of Linux observed via wireshark traces.
Fix the RST issue by sending RST only on out-of-range ACKs that occur
before the connection is fully established, as per RFC 793.
These problems were exposed during development of the 802.11 wireless
link layer; the 802.11 protocol has a failure mode that can easily
cause duplicated packets. The fixes were tested in a controlled way
by faking large numbers of duplicated packets in the rtl8139 driver.
Originally-fixed-by: Joshua Oreman <oremanj@rwcr.net>
"flags that are currently being sent". This allows at least one special
case (checking that we haven't already sent a FIN in tcp_rx_fin()) to be
collapsed.
I want to get to the point where any header in include/ reflects a
standard user-level header (e.g. a POSIX header), while everything that's
specific to gPXE lives in include/gpxe/. Headers that reflect a Linux
header (e.g. if_ether.h) should also be in include/gpxe/, with the same
name as the Linux header and, preferably, the same names used for the
definitions.
Michael Brown
Alexey Zaytsev
Nikhil Chandru Rao