How-to
install MFNOS on a pc-FlexNet link
Drafted by N1URO and edited by K2MF
Requires: MFNOS 1.29.2 or greater
March 21, 2003 ver-1.0.7
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As we all know, there have been issues with linking MFNOS
into a Flex-net machine, and running TCP/IP successfully
through Flexnet. After many hours spent, much debating,
and some decent code modifications by K2MF to MFNOS to
include yet another kluge for the behavior of Flex-net, N1URO
discovered some interesting things (some of which make
sense, some do not) that severely affected the behavior
of using an IP-VC or an AX.25 virtual circuit IP mode.
Whether you are using an AXIP link from NOS to Flexnet, a
KISS serial link from NOS to Flexnet or an RF AX.25 path
from NOS to digipeat through a Flexnet machine there are
many new things to consider due to the dynamic behaviors
of how pc-Flexnet operates.
Now to configure! Simply
connect NOS to pc-Flexnet as you normally would. I
personally happen to use the IPPD module for Flexnet and
use AXIP over ethernet between my MFNOS and Flexnet,
however a KISS serial interface may be treated in an
identical fashion.
In Flexnet, it is BEST to configure the NOS link so that
NOS' SSID is independent of the Flexnet machine. If you
don't, then it is quite possible (and very probable) that
Flexnet's kernel may try to take
control over the link layer 2 processes and prohibit the
IP-VC from getting through to NOS as shown below:
797: S2 P9 : N1URO-6>WA2SNA-1 v WA2SNA-6*
796: S0 P7 : WA2SNA-1>N1URO-6 v WB2ZII-9
Here we have an attempt to create an IP-VC through WA2SNA's
Flexnet from N1URO-6 [44.88.44.1] however because the NOS
SSID (WA2SNA-1) is aliased within the range of Flexnet (WA2SNA
0-14), the kernel is responding quicker than NOS is and
grabs control of the link layer 2. You will notice above
in process number 796 where the digipeater WA2SNA-6* is
omitted as proof of my theory. It is my personal
suggestion from many tests that (depending on your
individual configuration) if you are going to add an IP
gateway using MFNOS to your Flex-net site you plan out
your SSID range in Flexnet so that one non-user SSID (0
or 15) is allocated for the MFNOS node. If you are going
to allocate your Flexnet SSID range from 1-14, I would
suggest using -1 for MFNOS, and then set your SSID range
in Flexnet from 2-14 instead. This way if MFNOS
unfortunately locks up, freezes, vanishes, etc. for
whatever reason, or is overburdoned with another process
at the same time an IP-VC request comes in, the Flexnet
kernel will not answer the incoming request and create a
bogus link layer 2 connection. Here I have
Flexnetconfigured as N1URO (1-4) with NOS having the next
available SSID which is 5.
NOTE: Remember that in a pc-Flexnet network, when a
machine vanishes from the direct link, Flexnet will tell
the WAN to delete that machine from the Flexnet
destination lists, which also will successfully
disconnect the VC to the remote NOS machine.
On a wired AX.25 link, Flexnet will poll NOS
approximately every 2-3 minutes, so if you have a batch
file to restart NOS, you may wish to add a timer using
the DOS CHOICE command which will wait 3 minutes before
reloading NOS. This will give Flexnet a chance to see
that NOS is down and Flexnet will force a flush of VC
links to all other remote NOS ends. I personally observed
this one night where the path from K2BJG-8 to N1URO-5
failed during a TCP connection. While the fault was
within the Flexnet WAN cloud, Flexnet did disconnect the
VC at both NOS machines which automatically re-established
itself without disrupting the TCP connection when the
Flexnet path was restored.
Now let's first configure Flexnet properly.
Step 1:
Create your SSID range properly. The first SSID you
configure in Flexnet is also the node's primary SSID
Since I will give MFNOS an SSID of 5, I will configure
Flexnet to have the SSID range of 1-4 as follows:
=>mycall n1uro 1 4
Remember, if you are also a user on the network, do *not*
assign your nodes with an SSID of 0 or 15 or you will
lock yourself out of the network!
Step 2:
Configure your pc-Flexnet machine with a link to NOS as a
non-Flexnet destination that is routable within the
Flexnet WAN. You may do so by telling Flexnet to link the
interface number to NOScall-SSID. In my example, NOS
links on interface 3 so my link statement in pc-Flexnet
is:
=>L 3 N1URO-5 @ <-- @ = routable non-Flexnet aware
machine
Step 3:
You have to give the interface an SSID to enable
connections through the Flexnet digipeater. This must be
an unused interface SSID within the SSID range you
specified for Flexnet. You do this by using the parameter
command in Flexnet. In my example I will set an SSID of 2
to interface 3:
=>P S 2 3
Failure to do so will cause Flexnet to deny any and all
outbound link requests from NOS!
Flexnet's side is now complete.
Now let's configure NOS. I personally use independent
interface .src files for managing interfaces on my copy
of MFNOS which I call using the 'source <filename>'
command in autoexec.nos. The following exam-
ples are from my file called 'flexnet.src' in which I
name the interface "FlexNet". You will have to
adjust your timers accordingly to your specific needs.
The example below shows TCP settings for my interface
with an initial retry timer of 20 seconds (if no TCP ACK
is received) and it will use a linear timer type to back
itself off to a retry time of 1 full minute in case the
network is busy with other traffic such as PBBS mail
forwarding connections. The retries setting of 8 will let
TCP retry a maximum of 8 times in case the IP-VC fails
for whatever reason and needs restarting... thus allowing
TCP to pick up where it left off and not totally time out.
Using your existing 'ifconfig <interface>' commands
modify the following:
ifconfig FlexNet tcp blimit 3
ifconfig FlexNet tcp irtt 20000
ifconfig FlexNet tcp maxwait 60000
ifconfig FlexNet tcp retries 8
ifconfig FlexNet tcp timertype linear
Similar settings for the AX.25 layer can also be applied
to the interface. The example below shows that on link
layer 2, it will initially retry the packet within 5
seconds if it has not heard an ACK. This will give
Flexnet more than enough time to digipeat the packet for
you. The check timer is almost void since in reality all
it will be doing is checking the process link to Flexnet,
not the *real* virtual circuit. Flexnet itself will check
the IP-VC circuit to see whether or not the processes are
still valid and if not will close them. Again, you will
have to adjust these pending your own specific tests. It
is quite possible that your link to Flexnet itself is
very rapid however if the direct neighbor *to* the
Flexnet link is slow then we don't wish to flood the
network with retries too fast.
ifconfig FlexNet ax25 blimit 3
ifconfig FlexNet ax25 check 60000
ifconfig FlexNet ax25 irtt 5000
ifconfig FlexNet ax25 retries 10
ifconfig FlexNet ax25 timertype linear
Now let's tell AX.25 in NOS how to deal with the
interface, and add other things Flexnet likes such as
digipeating, etc.:
ax25 digipeat FlexNet on
This enables digipeating on the interface.
ax25 mode FlexNet vc
Set the default IP mode to virtual circuit. This also
forces any connections on this interface to prohibit a
mailbox server from launching unless the user 'kicks' the
mailbox with a packet having a Text PID (by pressing the
[Enter] key). This also blocks Flexnet's link polling
connections from showing up as user logins by you! In a
24 hour time period Flexnet can login as you to your NOS
mailbox over 200 times! That is just simply annoying and
irritating and presents you with bogus mailbox login
statistics. It is also a requirement of the kluge code (see
K2MF's modifications in 1.29.2).
Now add a route to the local Flexnet machine and let the
VC default IP mode comply with anti-polling/login kluges.
If there is no pre-existing AX.25 connection from Flexnet
to NOS, Flexnet will check the link by issuing an SABM (connect
request) packet to NOS. In compliance with normal AX.25
specifications, NOS will send a UA (unnumbered
acknowledgement) packet back to Flexnet which verifies to
Flexnet that the link is still valid and to which Flexnet
will then immediately send a DISC (disconnect request)
packet to NOS.
ax25 route perm n1uro-1 FlexNet # Add a route to FlexNet
N1URO (1-4)
ax25 hport FlexNet on # Log callsigns heard
ip hport FlexNet on # Log IP addresses heard
In autoexec.nos, be sure to have the following set:
ax25 jumpstart on
Jumpstart being on when the IP mode is VC has no meaning
during the initial setup of the VC but it is now
necessary for the K2MF kluge code to work properly.
Now let's configure the routing. Personally, I keep all
IP routing commands in a seperate file called 'iproutes.src'
(like with my interface configuration commands). If you
used the install.bat file, you will notice that these
commands (as with the interface commands) were included
in autoexec.nos. Either will work, but if you call
routines from external files they must be loaded with the
'source <drive>:/<path>/<filename>.src'
command in NOS. With that said, let's create an IP route
through N1URO (1-4) Flexnet to IPUE:AA1UE-8 MFNOS using
the following commands:
ax25 route perm aa1ue-8 FlexNet n1uro-1
This configures an AX.25 digipeated route to AA1UE-8
through Flexnet. It also raises the question, if the
Flexnet port SSID is -2, why did we use -1? This simply
helps NOS tap into the power of Flexnet's dynamic routing.
When a packet is received by Flexnet, it looks at four
possible ways to route it! First, it checks its Link list
to determine whether or not the callsign belongs to a
direct neighboring link. If it doesn't, then Flexnet
checks its Destinations list for the callsign. If the
callsign is not on the Destinations list, then Flexnet
checks its Mheard list for the callsign. If the callsign
is not on the Mheard list, then Flexnet will attempt to
connect to the callsign through all interfaces that have
SSIDs attached to them until the request times out or the
remote machine sends an acknowledgement to Flexnet, which
then puts the callsign on the MHeard list and Flexnet
will start to route to it that way. Also, remember that
the first SSID configured in Flexnet is its primary SSID.
ax25 jumpstart exclude aa1ue-8
Ignore any I (information) frame that contains a Text PID
from AA1UE-8 and also prohibit the mailbox server from
ever spawning to AA1UE-8, unless the source connection is
from a human (see K2MF's release notes for 1.29.2).
arp add 44.88.40.42 ax25 aa1ue-8 FlexNet
Create an ARP list entry to which the 'next IP gateway',
in this case 44.88.40.42, may be resolved.
route add 44.88.40.42/32 FlexNet 44.88.40.42
Create an IP route to this single machine using the
FlexNet interface. If 44.88.40.42 was routing for a
larger block, then that entire block may be added to the
route list instead.
Now load NOS and let's attempt to ping AA1UE-8 [44.88.40.42]
over my 1k2 user interface:
ipuro-R> ping aa1ue
ipuro-R> 44.88.40.42: rtt = 2680 ms
Let's also check the AX.25 virtual circuit:
ipuro-R> ax25 status
74e2 0 0 N1URO-5 AA1UE-8
FlexNet Connected and the AX.25 route:
ipuro-R> ax25 route
AA1UE-8 FlexNet Perm default
N1URO-1
At this point, all should be fine!
I hope this "How-to" helps you in not only
successfully routing IP through a Flexnet WAN cloud, but
also gives you some basic understanding as to how Flexnet
handles the link layer 2 encapsulation
of IP frames through a Flexnet digipeater node. Flexnet
is much more dynamic and robust in how it handles its AX.25
routing, and unlike our previous TheNet/X1J network is
more of a real time router where nodes come and go
quickly throughout the WAN. Also, in this configuration,
the Net/Rom layer 3 has been eliminated (which is good in
the sense that there is less packet overhead and more
room for data).
Comments are always welcomed.
73 de
Barry K2MF
Brian N1URO
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