This document discusses TCP connection repair in Linux. It introduces the problem of relocating one end of a TCP connection to another machine. The solution presented uses a repair mode for TCP connections, which are represented as pairs of sockets. New socket options and syscalls are introduced to manipulate TCP-specific attributes like sequence numbers, timestamps, and queues. This allows the connections to be disassembled and reassembled. Items for future work include improving support for transitional states, out-of-band data, connection shutdown, and connection tracking.

1. TCP repair in a nutshell
Pavel Emelyanov
Linux Plumbers, New Orleans, 2013

2. 2
Problem
take one end of a TCP connection
and relocate it on another machine

3. 3
Solution
TCP connection in Linux = a pair of sockets
Introduce a repair mode for it
– A set of new sockopts to manipulate TCP-specific things
• Seq-s
• Timestamps
• Handshake options
• Queues
– Sockets API syscalls “just do it”
With these two we can disassemble and assemble them
– Merged in Linux-3.5

4. 4
TODO
●
Transitional states
●
OOB data
●
Repair shutdown state
●
Connection tracking (netfilter)
●
What have we missed from TCP state machine?
●
Optimizations

5. 5
More info
CRIU sources git://git.criu.org/crtools.git
TCP repair example ${src}/tcp.c
Some docs http://criu.org/TCP_connection
/me xemul@openvz.org

6. 5
More info
CRIU sources git://git.criu.org/crtools.git
TCP repair example ${src}/tcp.c
Some docs http://criu.org/TCP_connection
/me xemul@openvz.org