AXIP(9) XR32 REFERENCE MANUAL 14/2/2013
NAME
AXIP -- AX25-over-IP Tunnelling.
DESCRIPTION
AXIP is AX25 "encapsulated" within IP datagrams. This enables
AX25 systems to communicate with each other via TCP/IP
networks (e.g. the Internet). The frame structure is as
follows:
.-----------.------------------------.
| IP header | AX25 frame |
'-----------'------------------------'
(20 bytes) (Typically 15-340 bytes)
The AX25 links created using AXIP can in turn support NetRom
and amateur TCP/IP, just like real radio links.
Setting Up AXIP Links
~~~~~~~~~~~~~~~~~~~~~~
Assuming you have a prospective AXIP partner, you would set
up an AXIP link as follows:
1) Configure and test IP routing between you and your
partner. If you don't have reliable IP routing there's no
point in proceeding!
If you are linking via the Internet, it makes sense to use
the Internet IP addresses for this purpose, rather than
the amateur (44.x.x.x) ones, because the routing is more
reliable and the throughput is faster.
2) If your partner has a dynamic IP address, they must have
an account with a "dynamic DNS" provider, and you must use
the hostname thus provided for all operations. If you use
the IP address instead, the link will stop working when
the address changes.
3) If you wish to use your prospective partner's hostname
(e.g. "g8pzt.ath.cx") instead of their IP address, your
system needs access to a Domain Name Server (DNS). This
would usually be provided by Windows nowadays, so you may
remove all "DNS=" lines from XROUTER.CFG.
4) If using the partner's hostname, verify that
"PING <hostname>" resolves the address correctly.
5) Add an AXIP interface to XROUTER.CFG as follows:
INTERFACE=7
TYPE=AXIP
MTU=256
ENDINTERFACE
(Choose the interface number to suit yourself).
This interface can support an unlimited number of AXIP
PORTs. You may define multiple interfaces if your ports
need different MTU's.
Only TYPE=AXIP and MTU= are required, all other parameters
are ignored (at present).
6) For each AXIP partner, add a PORT similar to this:
PORT=8
ID=AXIP link with WA3IP
INTERFACENUM=7 <-- Points to the INTERFACE above
IPLINK=55.73.88.69
FRACK=2000
RESPTIME=200
ENDPORT
You must specify at least ID, INTERFACENUM, and IPLINK.
IPLINK is the remote host's IP address or hostname. It is
more efficient to use IP addresses, if you are able to do
so, because it removes the need to resolve the hostnames,
but see (2) above. The assigned "protocol number" for
AXIP is 93 (decimal).
MAC parameters such as TXDELAY, TXTAIL, SLOTTIME, PERSIST,
FULLDUP, SOFTDCD etc. are meaningless for AXIP, but
FRACK, RESPTIME, PACLEN, MAXFRAME, QUALITY etc. operate
as normal.
On fast internet links you may wish to use a much lower
FRACK, say 2000ms, than on radio. It is not recommended
that you reduce it much below 1000ms, as it needs to be
*at least* twice the worst round-trip time plus the other
end's RESPTIME.
RESPTIME is probably the one which will have most effect
on the responsiveness of the AX25 link, because it
controls the time delay between receiving a packet and
sending an ACK. It should be just a little more than the
time it takes to receive a maximum length packet. For
example, at a data rate of 56Kbits/sec, a 256 byte packet
lasts less than 50msec, so RESPTIME=50 would be adequate.
However the timing jitter due to operating under Windows
means that RESPTIME should be more like 200ms.
7) If XR32 is indirectly connected to the Internet via an
intermediate router, that router will probably be using
some form of NAT (Network Address Translation) to share
one "public" IP address between several systems on your
LAN. The "front end" router will probably route outgoing
AXIP without problem, but it will not know where to send
incoming AXIP unless explicitly configured.
Configuring such a router for AXIP usually involves
specifying a protocol number (93 for AXIP), and the LAN IP
address of a machine to which it should be routed, i.e.
XR32's LAN IP address.
You are advised that not all domestic routers can be
configured to route incoming AXIP as it is not a
commercially recognised protocol. Some routers only allow
TCP and UDP port redirection, with no provision for any
other protocol. If you or your link partner have such a
router, you may need to consider AXUDP instead - see later.
8) Your link partner must set up a reciprocal arrangement,
i.e. their IPREMOTE must be set to your public IP address
or hostname.
If everything has been set up correctly, you should be able
to connect with your new neighbour node immediately, at least
at AX25 layer 2. You can test this by entering the command
"C n ALIAS-1", where n is the PORT number of your link, and
ALIAS is the node alias of your link partner. If this doesn't
work, you or your partner have made a mistake somewhere in the
configuration.
Even if everything is configured correctly, it may take a while
for NetRom to configure itself for the new link, as the nodes
need to exchange NODES brodcasts first. Once they have done
so, there should be no delays in future.
Notes
~~~~~
You may of course use AXIP to communicate between nodes on
the LAN, as long as they are not on the same machine.
If you have more than one node on your LAN using AXIP, your
Internet router is only able to direct incoming AXIP to *one*
of them. This means you can only have one AXIP node per
public IP address.
DO NOT set up an AXIP link to a link partner if you already
have an AXUDP link. This is a common mistake, and is likely
to cause problems!
Using one port per neighbour may seem wasteful, but it is a
reliable method, and it allows you to monitor exactly what is
going on.
IP Routing
~~~~~~~~~~
As mentioned earlier, you may route amateur IP (44.x.x.x) over
your new AXIP link, and are encouraged to do so. Whilst the
amprnet purists will argue that this is not as efficient as
IP-over-IP (since it uses a few more bytes), it is a LOT
easier to set up, and doesn't require that your domestic
router and operating system can route IP-over-IP (many
routers are not able to route incoming IP-over-IP to a
specific PC, and Windows' IP stack totally blocks IP-over-IP).
To route amateur IP over an AXIP link, simply add an IP route
entry directing the required subnet to your neighbour's IP
address on the AXIP port using datagram mode. For example, if
the AXIP port is port 8, and the link partner (44.136.20.2)
is able to accept all amprnet traffic for Australia, the entry
would look like this:
IP ROUTE ADD 44.136.0.0/16 44.136.20.2 8 d
The source IP address for this mode of routing is the
IPADDRESS of the AXIP port. Therefore, if XR32's main
IPADDRESS (in XROUTER.CFG) is not a 44-net address, you must
override it with a 44-net address on the AXIP port. If the
main IPADDRESS is a 44-net address, which is the recommended
configuration, do not specify IPADDRESS in the PORT
configuration block.
SEE ALSO
AXUDP(9) -- AX25-over-UDP Encapsulation
IP(1) -- IP Routing / Configuration Commands.
IPENCAP(9) -- IP-in-IP Encapsulation.
IPLINK(1) -- Display / Set a Port's IPLINK.
IP-PRIMER -- IP Addressing / Routing Primer.
IP-ROUTE.SYS(8) -- IP Routing / Configuration File.
IP-ROUTING(9) -- IP Routing With XR32.
XROUTER.CFG(8) -- Main Configuration File
AXIP(9) END OF DOCUMENT
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