DNS caching
===========

User experience may be greatly improved when dns is accelerated. Also, it
seems like a good idea to keep the number of packages being exchanged
between node and gateway as small as possible. In order to do this, a
DNS cache may be used on a node. The dnsmasq instance listening on port
53 on the node will be reconfigured to answer requests, use a list of
upstream servers and a specific cache size if the options listed below are
added to site.conf. Upstream servers are the DNS servers which are normally
used by the nodes to resolve hostnames (e.g. gateways/supernodes).

There are the following settings:
    servers
    cacheentries

If both options are set the node will cache as much DNS records as set with
'cacheentries' in RAM. The 'servers' list will be used to resolve the received
DNS queries if the request cannot be answered from cache.
If these settings do not exist, the cache is not intialized and RAM usage will not increase.

When next_node.name is set, an A record and an AAAA record for the
next-node IP address are placed in the dnsmasq configuration. This means that the content
of next_node.name may be resolved even without upstream connectivity.

::

  dns = {
    cacheentries = 5000,
    servers = { '2001:db8::1', },
  },

  next_node = {
    name = 'nextnode',
    ip6 = '2001:db8:8::1',
    ip4 = '198.51.100.1',
  }


The cache will be initialized during startup.
Each cache entry will occupy about 90 bytes of RAM.