Published: 20 Mar 2023
What is this?
mirage-nat contains module type definitions for a data store. Given a data store fulfilling that module type, mirage-nat also can generate modules for useful network address translation operations (e.g. adding entries based on incoming packets and translating packets if matching entries are present).
mirage-nat also contains an implementation of such a data store based on the lru library. Currently
Mirage_nat_lru is the only implementation; historical implementations using irmin as a backing store have been deprecated, but could be revived given sufficient interest.
Features and Limitations
mirage-nat allows users to add both source NAT (
NAT) and destination NAT (
mirage-nat currently supports translations between many addresses on a private IPv4 network and a single public IPv4 address. It is not capable of translating between IPv4 and IPv6, nor is it capable of translating IPv6 packets between networks.
mirage-nat knows how to translate TCP and UDP packets. It can also translate some ICMP types:
timestamp requests and replies
information requests and replies
echo requests and replies (in other words, ping should work)
mirage-nat makes no attempt to track connection state and currently does not expire rules based on time's passage.
Mirage_nat_lru expires the least recently used rules in response to memory pressure. In practice, this means rules will stick around as long as there's space for them, with no consideration for whether communication between hosts is still occurring. Notably, remote hosts which have been contacted by a host on the private network may be able to send traffic back through the NAT long after the host thinks the connection has been terminated.
example/ directory contains an example MirageOS unikernel which uses
Mirage_nat_lru to provide source NATting between a private network and a public one. Try
mirage configure --help in that directory for information on configuration parameters, and read
unikernel.ml for more on how it works.
To get started, you'll need a "public" network (one from which the Internet is accessible) and a "private" network (one which doesn't have outside access; this will be provided by the unikernel once it's online). Configure the unikernel with the correct public network information, and an IP address on the private network. For example, to set up a unikernel with a public network on 192.168.3.1/24, and a private 10.0.0.0/24 network, if configured for Xen:
mirage configure -t xen --public-ipv4=192.168.3.1/24 --public-ipv4-gateway=192.168.3.254 --private-ipv4=10.0.0.1/24
Then follow the usual MirageOS workflow:
make depend make
and start the unikernel as appropriate for the hypervisor:
sudo xl create simple_nat.xl -c
To see more console output, try increasing the log level with the
-l argument to