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Add support for TCP keepalives, for both socket and direct #338

merged 10 commits into from Feb 15, 2018


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@djs55 djs55 commented Sep 5, 2017

This is an implementation of mirage/mirage-protocols#8

The socket implementation uses setsockopt on Unix-like systems and WSAIoctl on Win32.

The direct implementation uses the same algorithm, implemented in the keepalive module. There are tests for the core logic (which is free of I/O) and an end-to-end test of the TCP stack with a broken network.

This PR also includes

  • a rename of Sequence.incr to Sequence.succ to follow the pattern used by Int32, Int64 etc
  • merging the TCP Pcb and Flow modules since Flow was only a thin wrapper over Pcb
@djs55 djs55 force-pushed the djs55:keepalive2 branch from 530abb3 to 343d331 Sep 6, 2017
djs55 added 8 commits Sep 6, 2017
The `Flow` module was only a thin layer on top of `Pcb` with slightly
different types. This patch makes the module contents the same and
will allow us to delete one of them.

Signed-off-by: David Scott <>
Signed-off-by: David Scott <>
Since this function has type `t -> t` it is the same as `succ` in the
standard library modules Int32, Int64 etc. The function `incr` would
have type `t -> unit`

Signed-off-by: David Scott <>
Signed-off-by: David Scott <>
The socket stack uses `setsockopt` and `WSAIoctl` support for Linux,
Darwin and Win32. Note that Linux and Darwin use second resolution while
Win32 supports millisecond resolution.

Signed-off-by: David Scott <>
The direct stack implements the same strategy as Linux and the BSDs i.e.

- wait until the connection has been idle for an initial period
- transmit a finite number of "probes" with a constant interval until
  either a packet is received (in which case the connection is alive!)
  or we run out of packets to transmit (in which case the connection is

Note that keepalives are disabled by default.

Signed-off-by: David Scott <>
There are 2 types of test:

1. tests of the keepalive logic: this verifies that the correct number
   probes are sent and the connection is declared dead after all probes
   have been lost. These tests are unit tests of the ``
2. an end-to-end stack test: this verifies that a connection is eventually
   terminated if the network is set to drop all traffic and keepalives
   are enabled.

Signed-off-by: David Scott <>
The CI needs to build mirage-{protocols,stack,tcpip} and vpnkit

Signed-off-by: David Scott <>
@djs55 djs55 force-pushed the djs55:keepalive2 branch from 343d331 to 9b4d3c2 Feb 13, 2018
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@djs55 djs55 commented Feb 14, 2018

Looks like a -safe-string problem:

# File "test/", line 114, characters 42-46:
# Error: This expression has type string but an expression was expected of type
#          bytes
I think this slipped through because the PR build didn't have 4.06 in
the travis matrix, but master does.

Signed-off-by: David Scott <>
Signed-off-by: David Scott <>
@djs55 djs55 force-pushed the djs55:keepalive2 branch from 074e457 to a5c2cc8 Feb 15, 2018
@djs55 djs55 merged commit db75766 into mirage:master Feb 15, 2018
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avsm added a commit to avsm/opam-repository that referenced this pull request Feb 3, 2019

* Use `Lwt_dllist` instead of `Lwt_sequence`, due to the latter being deprecated
  upstream in Lwt (ocsigen/lwt#361) (mirage/mirage-tcpip#388 by @avsm).
* Remove arpv4 and ethif sublibraries, now provided by ethernet and arp-mirage
  opam packages (mirage/mirage-tcpip#380 by @hannesm).
* Upgrade from jbuilder to dune (mirage/mirage-tcpip#391 @avsm)
* Switch from topkg to dune-release (mirage/mirage-tcpip#391 @avsm)

### v3.6.0 (2019-01-04)

* The IPv4 implementation now supports reassembly of IPv4 fragments (mirage/mirage-tcpip#375 by @hannesm)
  - using a LRU cache using up to 256KB memory
  - out of order fragments are supported
  - maximum number of fragments is 16
  - timeout between first and last fragment is 10s
  - overlapping fragments are dropped

* IPv6: use correct timeout value after first NS message (mirage/mirage-tcpip#334 @djs55)

* Use `Ipaddr.pp` instead of `Ipaddr.pp_hum` due to upstream
  interface changes (mirage/mirage-tcpip#385 @hannesm).

### v3.5.1 (2018-11-16)

* socket stack (tcp/udp): catch exception in recv_from and accept (mirage/mirage-tcpip#376 @hannesm)
* use mirage-random-test for testing (Stdlibrandom got removed from mirage-random>1.2.0, mirage/mirage-tcpip#377 @hannesm)

### v3.5.0 (2018-09-16)

* Ipv4: require Mirage_random.C, used for generating IPv4 identifier instead of using OCaml's stdlib Random directly (mirage/mirage-tcpip#371 @hannesm)
* Tcp: use entire 32 bits at random for the initial sequence number, thanks to Spencer Michaels and Jeff Dileo of NCC Group for reporting (mirage/mirage-tcpip#371 @hannesm)
* adjust to mirage-protocols 1.4.0 and mirage-stack 1.3.0 changes (mirage/mirage-tcpip#371 @hannesm)
  Arp no longer contains the type alias ethif
  Ethif no longer contains the type alias netif
  Static_ipv4 no longer contains the type alias ethif and prefix
  Ipv6 no longer contains the type alias ethif and prefix
  Mirage_protocols_lwt.IPV4 no longer contains the type alias ethif
  Mirage_protocols_lwt.UDPV4 and TCPV4 no longer contain the type alias ip
* remove unused types: 'a config, netif, and id from socket and direct stack (mirage/mirage-tcpip#371 @hannesm)
* remove usage of Result, depending on OCaml >= 4.03.0 (mirage/mirage-tcpip#372 @hannesm)

### v3.4.2 (2018-06-15)

Note the use of the new TCP keep-alive feature can cause excessive amounts
of memory to be used in some circumstances, see

* Ensure a zero UDP checksum is sent as 0xffff, not 0x0000 (mirage/mirage-tcpip#359 @stedolan)
* Avoid leaking a file descriptor in the socket stack if the connection fails (mirage/mirage-tcpip#363 @hannesm)
* Avoid raising an exception with `` when `write` fails in the socket stack (mirage/mirage-tcpip#363 @hannesm)
* Ignore `EBADF` errors in `close` in the socket stack (mirage/mirage-tcpip#366 @hannesm)
* Emit a warning when TCP keep-alives are used (mirage/mirage-tcpip#368 @djs55)

### v3.4.1 (2018-03-09)

* expose tcp_socket_options in the socket stack, fixing downstream builds (mirage/mirage-tcpip#356 @yomimono)
* add missing dependencies and constraints (mirage/mirage-tcpip#354 @yomimono, mirage/mirage-tcpip#353 @rgrinberg)
* remove leftover ocamlbuild files (mirage/mirage-tcpip#353 @rgrinberg)

### v3.4.0 (2018-02-15)

* Add support for TCP keepalives (mirage/mirage-tcpip#338 @djs55)
* Fix TCP deadlock (mirage/mirage-tcpip#343 @mfp)
* Update the CI to test OCaml 4.04, 4.05, 4.06 (mirage/mirage-tcpip#344 @yomimono)

### v3.3.1 (2017-11-07)

* Add an example for user-space `ping`, and some socket ICMPv4 fixes (mirage/mirage-tcpip#336 @djs55)
* Make tcpip safe-string-safe (and buildable by default on OCaml 4.06.0) (mirage/mirage-tcpip#341 @djs55)

### v3.3.0 (2017-08-08)

* Test with current mirage-www master (mirage/mirage-tcpip#323 @yomimono)
* Improve the Tcp.Wire API (mirage/mirage-tcpip#325 @samoht)
* Add dependency from stack-unix to io-page-unix (@avsm)
* Replace dependency on cstruct.lwt with cstruct-lwt (mirage/mirage-tcpip#322 @yomimono)
* Update to lwt 3.0 (mirage/mirage-tcpip#326 @samoht)
* Replace oUnit with alcotest (mirage/mirage-tcpip#329 @samoht)
* Fix stub linking on Xen (mirage/mirage-tcpip#332 @djs55)
* Add support for ICMP sockets on Windows (mirage/mirage-tcpip#333 @djs55)

### v3.2.0 (2017-06-26)

* port to jbuilder. Build time is now roughly 4-5x faster than the old oasis-based build system.
* packs have been replaced by module aliases.

### v3.1.4 (2017-06-12)

* avoid linking to cstruct.ppx in the compiled library and only use it at build time (mirage/mirage-tcpip#316 @djs55)
* use improved packet size support in `mirage-vnetif>=0.4.0` to test the MTU fixes in mirage/mirage-tcpip#313.

### v3.1.3 (2017-05-23)

* involve the IP layer's MTU in the TCP MSS calculation (hopefully correctly) (mirage/mirage-tcpip#313, by @yomimono)

### v3.1.2 (2017-05-14)

* impose a maximum TCP MSS of 1460 to avoid sending over-large datagrams on 1500 MTU links
  (mirage/mirage-tcpip#309, by @hannesm)

### v3.1.1 (2017-05-14)

* fix parsing 20-byte cstructs as ipv4 packets (mirage/mirage-tcpip#307, by @yomimono)
* udp: payload length parse fix (mirage/mirage-tcpip#307, by @yomimono)
* support lwt >= 2.7.0 (mirage/mirage-tcpip#308, by @djs55)

### v3.1.0 (2017-03-14)

* implement MTU setting and querying in the Ethernet module (compatibility with mirage-protocols version 1.1.0), and use this value to inform TCP's MSS. (mirage/mirage-tcpip#288, by @djs55)
* rename the ~payload argument of TCP/UDP marshallers to `~payload_len`, in an attempt to clarify that the payload will not be copied to the Cstruct.t returned by these functions (mirage/mirage-tcpip#301, by @talex5)
* functorize ipv6 over a random implementation (mirage/mirage-tcpip#298, by @olleolleolle and @hannesm)
* add tests for sending and receiving UDP packets over IPv6 (mirage/mirage-tcpip#300, by @mattgray)
* avoid float in TCP RTO calculations. (mirage/mirage-tcpip#295, by @olleolleolle and @mattgray)
* numerous bugfixes in header marshallers and unmarshallers (mirage/mirage-tcpip#301, by @talex5 and @yomimono)
* replace polymorphic equality in `_packet.equals` functions (mirage/mirage-tcpip#302, by @yomimono)

### v3.0.0 (2017-02-23)

* adapt to MirageOS 3 API changes (*many* PRs, from @hannesm, @samoht, and @yomimono):
  - replace error polyvars in many functions with result types
  - define and use error types
  - `connect` in various modules now returns the device directly or raises an exception
  - refer to mirage-protocols and mirage-stacks, rather than mirage-types
* if no UDP source port is given to UDP.write, choose a random one (mirage/mirage-tcpip#272, by @hannesm)
* remove `Ipv4.Routing.No_route_to_destination_address` exception; treat routing failures as normal packet loss in TCP (mirage/mirage-tcpip#269, by @yomimono)
* Ipv6.connect takes a list of IPs (mirage/mirage-tcpip#268, by @yomimono)
* remove exception "Refused" in TCP (mirage/mirage-tcpip#267, by @yomimono)
* remove DHCP module. Users may be interested in the replacement charrua-core (mirage/mirage-tcpip#260, by @yomimono)
* move Ipv4 to Static\_ipv4, which can be used by other IPv4 modules with their own configuration logic (mirage/mirage-tcpip#260, by @yomimono)
* remove `mode` from STACKV4 record and configuration; Ipv4.connect now requires address parameters and the module exposes no methods for modifying them. (mirage/mirage-tcpip#260, by @yomimono)
* remove unused `id` types no longer required by mirage-types (mirage/mirage-tcpip#255, by @yomimono)
* overhaul how `random` is used and handled (mirage/mirage-tcpip#254 and others, by @hannesm)
* fix redundant `memset` that zeroed out options in Tcp\_packet.Marshal.into\_cstruct (mirage/mirage-tcpip#250, by @balrajsingh)
* add vnetif backend for triggering fast retransmit in iperf tests (mirage/mirage-tcpip#248, by @MagnusS)
* fixes for incorrect timer values (mirage/mirage-tcpip#247, by @balrajsingh)
* add vnetif backend that drops packets with no payload (mirage/mirage-tcpip#246, by @MagnusS)
* fix a race when closing test pcap files (mirage/mirage-tcpip#246, by @MagnusS)

### v2.8.1 (2016-09-12)

* Set the TCP congestion window correctly when going into fast-recovery mode. (mirage/mirage-tcpip#244, by @balrajsingh)
* When TCP packet loss is discovered by timeout, allow transition into fast-recovery mode. (mirage/mirage-tcpip#244, by @balrajsingh)

### v2.8.0 (2016-04-04)

* Provide an implementation for the ICMPV4 module type defined in mirage-types 2.8.0.  Remove default ICMP handling from the IPv4 module, but preserve it in tcpip-stack-direct. (mirage/mirage-tcpip#195 by @yomimono)
* Explicitly require the use of an OCaml compiler >= 4.02.3 . (mirage/mirage-tcpip#195 by @yomimono)
* Explicitly depend on `result`. (mirage/mirage-tcpip#195 by @yomimono)

### v2.7.0 (2016-03-20)

* Raise Invalid\_argument if given an invalid port number in listen_{tcp,udp}v4
  (mirage/mirage-tcpip#173 by @matildah and mirage/mirage-tcpip#175 by @hannesm)
* Improve TCP options marshalling/unmarshalling (mirage/mirage-tcpip#174 by @yomimono)
* Add state tests and fixes for closure conditions (mirage/mirage-tcpip#177 mirage/mirage-tcpip#176 by @yomimono)
* Remove bogus warning (mirage/mirage-tcpip#178 by @talex5)
* Clean up IPv6 stack (mirage/mirage-tcpip#179 by @nojb)
* RST checking from RFC5961 (mirage/mirage-tcpip#182 by @ppolv)
* Transform EPIPE exceptions into `Eof (mirage/mirage-tcpip#183 by @djs55)
* Improve error strings in IPv4 (mirage/mirage-tcpip#184 by @yomimono)
* Replace use of cstruct.syntax with cstruct.ppx (mirage/mirage-tcpip#188 by @djs55)
* Make the Unix subpackages optional, so the core builds on Win32
  (mirage/mirage-tcpip#191 by @djs55)

### v2.6.1 (2015-09-15)

* Add optional arguments for settings in ip v6 and v4 connects (mirage/mirage-tcpip#170, by @Drup)
* Expose `Ipv4.Routing.No_route_to_destination_address` (mirage/mirage-tcpip#166, by @yomimono)

### v2.6.0 (2015-07-29)

* ARP now handles ARP frames, not Ethernet frames with ARP payload
  (mirage/mirage-tcpip#164, by @hannesm)
* Check length of received ethernet frame to avoid cstruct exceptions
  (mirage/mirage-tcpip#117, by @hannesm)
* Pull arpv4 module out of ipv4. Also add unit-tests for the newly created
  ARP library  (mirage/mirage-tcpip#155, by @yomimono)

### v2.5.1 (2015-07-07)

* Fix regression introduced in 2.5.0 where packet loss could lead to the
  connection to become very slow (mirage/mirage-tcpip#157, MagnusS, @talex5, @yomimono and
* Improve the tests: more logging, more tracing and compile to native code when
  available, etc (@MagnusS and @talex5)
* Do not raise `Invalid_argument("Lwt.wakeup_result")` everytime a connection
  is closed. Also now pass the raised exceptions to `Lwt.async_exception_hook`
  instead of ignoring them transparently, so the user can decide to shutdown
  its application if something wrong happens (mirage/mirage-tcpip#153, mirage/mirage-tcpip#156, @yomomino and @talex5)
* The `channel` library now lives in a separate repository and is released
  separately (mirage/mirage-tcpip#159, @samoht)

### v2.5.0 (2015-06-10)

* The test runs now produce `.pcap` files (mirage/mirage-tcpip#141, by @MagnusS)
* Strip trailing bytes from network packets (mirage/mirage-tcpip#145, by @talex5)
* Add tests for uniform packet loss (mirage/mirage-tcpip#147, by @MagnusS)
* fixed bug where in case of out of order packets the ack and window were set
  incorrectly (mirage/mirage-tcpip#140, mirage/mirage-tcpip#146)
* Properly handle RST packets (mirage/mirage-tcpip#107, mirage/mirage-tcpip#148)
* Add a `Log` module to control at runtime the debug statements which are
  displayed (mirage/mirage-tcpip#142)
* Writing in a PCB which does not have the right state now returns an error
  instead of blocking (mirage/mirage-tcpip#150)

### v2.4.3 (2015-05-05)

* Fix infinite loop in `Channel.read_line` when the line does not contain a CRLF
  sequence (mirage/mirage-tcpip#131)

### v2.4.2 (2015-04-29)

* Fix a memory leak in `Channel` (mirage/mirage-tcpip#119, by @yomimono)
* Add basic unit-test for channels (mirage/mirage-tcpip#119, by @yomimono)
* Add alcotest testing templates
* Modernize Travis CI scripts

### v2.4.1 (2015-04-21)

* Merge between 2.4.0 and 2.3.1

### v2.4.0 (2015-03-24)

* ARP improvements (mirage/mirage-tcpip#118)

### v2.3.1 (2015-03-31)

* Do not raise an assertion if an IP frame has extra trailing bytes (mirage/mirage-tcpip#221).

### v2.3.0 (2015-03-09)

* Fix `STACKV4` for the `DEVICE` signature which has `connect` removed
  (in Mirage types 2.3+).

### v2.2.3 (2015-03-09)

* Add ICMPv6 error reporting functions (mirage/mirage-tcpip#101)
* Add universal IP address converters (mirage/mirage-tcpip#108)
* Add `error_message` functions for human-readable errors (mirage/mirage-tcpip#98)
* Improve debug logging for ICMP Destination Unreachable packets.
* Filter incoming frames by MAC address to stop sending unnecessary RSTs. (mirage/mirage-tcpip#114)
* Unhook unused modules `Sliding_window` and `Profiler` from the build. (mirage/mirage-tcpip#112)
* Add an explicit `connect` method to the signatures. (mirage/mirage-tcpip#100)

### v2.2.2 (2015-01-11)

* Readded tracing and ARP fixes which got accidentally reverted in the IPv6
  merge. (mirage/mirage-tcpip#96)

### v2.2.1 (2014-12-20)

* Use `Bytes` instead of `String` to begin the `-safe-string` migration in OCaml
  4.02.0 (mirage/mirage-tcpip#93).
* Remove dependency on `uint` to avoid the need for a C stub (mirage/mirage-tcpip#92).

### v2.2.0 (2014-12-18)

Add IPv6 support. This changeset minimises interface changes to the existing
`STACKV4` interfaces to faciliate a progressive merge.  The only visible
interface changes are:

* `IPV4.set_ipv4_*` functions have been renamed `IPV4.set_ip_*` because they
  are shared between IPV4 and IPV6.
* `IPV4.get_ipv4` and `get_ipv4_netmask` now return a `list` of `Ipaddr.V4.t`
  (again because this is the common semantics with IPV6.)
* Several types that had `v4` in their names (like `IPV4.ipv4addr`) have lost
  that particle.

### v2.1.1 (2014-12-12)

* Improve console printing for the DHCP client to output line
  breaks properly on Xen consoles.

### v2.1.0 (2014-12-07)

* Build Xen stubs separately, with `CFLAGS` from `mirage-xen` 2.1.0+.
  This allows us to use the red zone under x86_64 Unix again.
* Adding tracing labels and counters, which introduces a new dependency on the
  `mirage-profile` package.

### v2.0.3 (2014-12-05)

* Fixed race waiting for ARP response (mirage/mirage-tcpip#86).
* Move the the code that configures IPv4 address, netmask and gateways
  after receiving a successful lease out of the `Dhcp_clientv4` module
  and into `Stackv4` (mirage/mirage-tcpip#87)

### v2.0.2 (2014-12-01)

* Add IPv4 multicast to MAC address mapping in IPv4 output processing
  (mirage/mirage-tcpip#81 from Luke Dunstan).
* Improve formatting of DHCP console logging, including printing out options
* Build with -mno-red-zone on x86_64 to avoid stack corruption on Xen (mirage/mirage-tcpip#80).

### v2.0.1 (2014-11-04)

* Fixed race condition in the signalling between the rx/tx threads under load.
* Experimentally switch to immediate ACKs in TCPv4 by default instead of delayed ones.

### v2.0.0 (2014-11-02)

* Moved 1s complement checksum C code here from mirage-platform.
* Depend on `Console_unix` and `Console_xen` instead of `Console`.
* [socket] Do not return an `Eof` when writing 0-length buffer (mirage/mirage-tcpip#76).
* [socket] Accept callbacks now run in async threads instead of being serialised

### v1.1.6 (2014-07-20)

* Quieten down the stack logging rate by not announcing IPv6 packet discards.
* Raise exception `Bad_option` for unparseable or invalid TCPv4 options (mirage/mirage-tcpip#57).
* Fix linking error with module `Tcp_checksum` by lifting it into top library
* Add `opam` file to permit easier local pinning, and fix Travis to use this.

### v1.1.5 (2014-06-18)

* Ensure that DHCP completes before the application is started, so that
  unikernels that establish outgoing connections can do so without a race.
  (fix from Mindy Preston in mirage/mirage-tcpip#53, followup in mirage/mirage-tcpip#55)
* Add `echo`, `chargen` and `discard` services into the `examples/`
  directory. (from Mindy Preston in mirage/mirage-tcpip#52).

### v1.1.4 (2014-06-03)

* [tcp] Fully process the last `ACK` in a 3-way handshake for server connections.
  This ensures that a `FIN` is correctly transmitted upon application-initiated
  connection close. (fix from Mindy Preston in mirage/mirage-tcpip#51).

### v1.1.3 (2014-03-01)

* Expose IPV4 through the STACKV4 interface.

### v1.1.2 (2014-03-27)

* Fix DHCP variable length option parsing for MTU responses, which
  in turns improves robustness on Amazon EC2 (fix from @yomimono
  via mirage/mirage-tcpip#48)

### v1.1.1 (2014-02-21)

* Catch and ignore top-level socket exceptions (mirage/mirage-tcpip#219).
* Set `SO_REUSEADDR` on listening sockets for Unix (mirage/mirage-tcpip#218).
* Adapt the Stack interfaces to the v1.1.1 mirage-types interface
  (see mirage/mirage#226 for details).

### v1.1.0 (2014-02-03)

* Rewrite of the library as a set of functors that parameterize the
  stack across the `V1_LWT` module types from Mirage 1.1.x.  This removes
  the need to compile separate Xen and Unix versions of the stack.

### v0.9.5 (2013-12-08)

* Build for either Xen or Unix, depending on the value of the `OS` envvar.
* Shift to the `mirage-types` 0.5.0+ interfaces, which breaks the
  socket backend (temporarily).
* Port the direct stack to the new interfaces.
* Add Travis CI scripts.

### v0.9.4 (2013-08-09)

* Use the `Ipaddr` external library and remove the Homebrew
  equivalents in `Nettypes`.

### v0.9.3 (2013-07-18)

* Changes in module Manager: Removed some functions from the `.mli
  (plug/unplug) and added some modifications in the way the Manager
  interacts with the underlying module Netif. The Netif.create function
  does not take a callback anymore.

### v0.9.2 (2013-07-09)

* Improve TCP state machine for connection teardown.
* Limit fragment number to 8, and coalesce buffers if it goes higher.
* Adapt to mirage-platform-0.9.2 API changes.

### v0.9.1 (2013-06-12)

* Depend on mirage-platform-0.9.1 direct tuntap interfaces.
* Version bump to catch up with mirage-platform.

### v0.5.2 (2013-02-08)

* Encourage scatter-gather I/O all the time, rather than playing tricks
  with packet header buffers. This simplifies the output path considerably
  and cuts minor heap allocations down.
* Install the packed `cmx` along with the `cmxa` to ensure that the
  compiler can do cross-module optimization (this is not a fatal error,
  but will impact performance if the `cmx` file is not present).

### v0.5.1 (2012-12-20)

* Update socket stack to use Cstruct 0.6.0 API

### v0.5.0 (2012-12-20)

* Update Cstruct API to 0.6.0
* [tcp] write now blocks if the write buffer and write window are full

### v0.4.1 (2012-12-14)

* Add iperf self-test that creates two VIFs and transmits across
  them. This is a useful local test which stresses the bridge
  code using just one VM.
* Add support for attaching existing devices when initialising the
  network manager, via an optional `attached` parameter.
* Constrain TCP connect to be a `unit Lwt.t` instead of a polymorphic
  return value.
* Expose IPv4 netmask function.
* Reduce ARP verbosity to the console.
* Fix TCP fast recovery to wait until all in-flight packets are
  acked, rather then exiting early.

### v0.4.0 (2012-12-11)

* Require OCaml-4.00.0 or higher, and add relevant build fixes
  to deal with module packing.

### v0.3.1 (2012-12-10)

* Fix the DHCP client marshalling for IPv4 addresses.
* Expose the interface MAC address in the Manager signature.
* Tweak TCP ISN calculation to be more friendly on a 32-bit host.
* Add Manager.create ?devs to control the number of Netif devices
  constructed by default.
* Add Ethif.set/disable_promiscuous to permit directly tapping
  a network interface.

### v0.3.0 (2012-09-04)

* Initial public release.
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