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.. _dev_cnat:
.. toctree::
Cloud NAT
=========
Overview
________
This plugin covers specific NAT use-cases that come mostly
from the container networking world. On the contraty of the
NAT concepts used for e.g. a home gateway, there is no notion
of 'outside' and 'inside'. We handle Virtual (or Real) IPs and
translations of the packets destined to them
Terminology & Usage
___________________
Setting up the NAT will consist in the creation of a ``translation``
that has several backends. A ``translation`` is 3-tuple containing :
a fully qualified IP address a port and a protocol. All packets
destined to it (ip, port) will then choose one of the backends,
and follow its rewrite rules.
A ``backend`` consists of four rewrites components (source & destination
address, source & destination port) that shall be applied to packets
on the way in, and reverted on the way back.
Backends are equally load-balanced with a flow hash. The choice
of a ``backend`` for a flow will trigger the creation of a NAT ``session``,
that will store the packet rewrite to do and the one to undo
until the flow is reset or a timeout is reached
A ``session`` is a fully resolved 9-tuple of ``src_ip, src_port, dest_ip, dest_port, proto``
to match incoming packets, and their new attributes ``new_src_ip, new_src_port, new_dest_ip, new_dest_port``. It allows for ``backend`` stickyness and a fast-path for established connections.
These ``sessions`` expire after 30s for regular ``sessions`` and 1h for estabished
TCP connections. These can be changed in vpp's configuration file
.. code-block:: console
cnat {
session-max-age 60
tcp-max-age 3600
}
Traffic is matched by inserting FIB entries, that are represented
by a ``client``. These maintain a refcount of the number of ``sessions``
and/or ``translations`` depending on them and be cleaned up when
all have gone.
Translating Addresses
---------------------
In this example, all packets destined to ``30.0.0.2:80`` will be
rewritten so that their destination IP is ``20.0.0.1`` and destination
port ``8080``. Here ``30.0.0.2`` has to be a virtual IP, it cannot be
assigned to an interface
.. code-block:: console
cnat translation add proto TCP vip 30.0.0.2 80 to ->20.0.0.1 8080
If ``30.0.0.2`` is the address of an interface, we can use the following
to do the same translation, and additionnaly change the source.
address with ``1.2.3.4``
.. code-block:: console
cnat translation add proto TCP real 30.0.0.2 80 to 1.2.3.4->20.0.0.1 8080
To show existing translations and sessions you can use
.. code-block:: console
cnat show session verbose
cant show translation
SourceNATing outgoing traffic
-----------------------------
A independant part of the plugin allows changing the source address
of outgoing traffic on a per-interface basis.
In the following example, all traffic comming from ``tap0`` and NOT
going to ``20.0.0.0/24`` will be source NAT-ed with ``30.0.0.1``.
On the way back the translation will be undone.
NB: ``30.0.0.1`` should be and address known to the FIB (e.g. the
address assigned t
}
/*
* Copyright (c) 2015 Cisco and/or its affiliates.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
Copyright (c) 2001, 2002, 2003 Eliot Dresselhaus
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#ifdef CLIB_LINUX_KERNEL
#include <linux/unistd.h>
#endif
#ifdef CLIB_UNIX
#include <unistd.h>
|
