[bug #40293] tftp implementation doesn't re-transmit ACKs

[Tyson Whitehead]

URL:
  <http://savannah.gnu.org/bugs/?40293>

                 Summary: tftp implementation doesn't re-transmit ACKs
                 Project: GNU GRUB
            Submitted by: twhitehead
            Submitted on: Thu 17 Oct 2013 06:41:26 PM GMT
                Category: Network
                Severity: Major
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: Bazaar - trunk
         Reproducibility: None
         Planned Release: None

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Details:

Description of problem:

Grub2's TFTP implementation does not send another ACK upon receiving the last
data packet a second time.  This results in the TFTP transfer breaking down in
the face of packet loss and ending in a timeout error.  This looks like so

server -> data 1 -> grub
grub -> ack 1 -> server
server -> data 2 -> grub
grub -> ack 2 -> server
.
.
.
server -> data k -> grub
grub -> ack k -> (lost in the network)
server -> data k -> grub
server -> data k -> grub
server -> data k -> grub
server -> data k -> grub
.
.
.

until Grub reports a timeout error waiting for data k+1.

The relevant part of RFC 1350 is (Section 2 -- Overview)

"If a packet gets lost in the network, the intended recipient will timeout and
may retransmit his last packet (which may be data or an acknowledgment), thus
causing the sender of the lost packet to retransmit that lost packet.
...
Notice that both machines involved in a transfer are considered senders and
receivers.  One sends data and receives acknowledgments, the other sends
acknowledgments and receives data."

http://www.ietf.org/rfc/rfc1350.txt

I'm attaching a patch to get grub to re-transmit the last ack upon receiving
the last data packet again.  It works for me.



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File Attachments:


-------------------------------------------------------
Date: Thu 17 Oct 2013 06:41:26 PM GMT  Name: tftp-ack.patch  Size: 3kB   By:
twhitehead

<http://savannah.gnu.org/bugs/download.php?file_id=29394>

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