[FlexNet] RE:TCP/IP and FlexNet

[John Papson]

Hello All:

Here is a nice piece that one of the local TCP/IP Groups wrote about 
interfacing FlexNet and TCP/IP...

Originally they were very opposed to Flex, but now are supporting it !

73

John WB2CIK

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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
=========================================

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 sug-
gestion from many tests that (depending on your individual configura-
tion) 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 Flexnet configured as N1URO (1-4) with NOS having the next avail-
able 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 dis-
connect 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 inter-
face.  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 con-
nections 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 pol-
ling 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-exist-
ing 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 ack-
nowledgement) 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 inter-
face 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 Flex-
net 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 under-
standing 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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