XRPi Documentation - Interfacing

Ports

What Are Ports?

A PORT is a point of interaction between XRPi's central "core" and the INTERFACES which connect to the world outside XRPi. You cannot have a PORT without having an INTERFACE to attach it to.

All AX25 operations are PORT-based, where a PORT usually corresponds to a single radio frequency. Ports allow XRPi to direct output to a specific device, and receive input from that device.

Each port is attached to a CHANNEL on an INTERFACE. Some interfaces are single-channel, and can therefore support only one PORT. Others are multi-channel, and can have several ports attached to them.

For example, an ASYNC interface connected to a PSTN modem supports only one channel of communication with the modem, therefore it can only support one port. But an ASYNC interface using KISS protocol can support a multi-channel TNC, whereby each channel is connected to a seperate radio on its own frequency, thus there would be one PORT for each channel.

For historical reasons, XRPi will not run unless there is at least one PORT.

Defining Ports in XRPi

XRPi ports are configured using PORT definition blocks within the GLOBAL section of XROUTER.CFG. The blocks start with the keyword PORT and end with ENDPORT.

They contain directives of the general form <keyword>=<value>, each on a separate line. (If you do not understand the significance of the <>, please see the conventions section). Keywords are not case sensitive, and may be specified in any order.

For example:

	PORT=2
		(directives here)
	ENDPORT

Some directives are mandatory, but most are optional. The full range of port keywords is summarised below (*=mandatory):

PORT Keywords - Overview

        APPLMASK        Controls which applications are visible
        APRSPATH        Default digipeater path for APRS
        BCAST           List of destinations for "broadcasting"
        BCFROM          Callsigns who may broadcast
        CFLAGS          Controls AX25 up/downlinking
        CHANNEL         Channel to use on interface (A)
        CHATALIAS       Port override for global chatalias
        CHATCALL        Port override for global chatcall
        CWID            Text to send in CW every 30' (SCC only)
        DHCP            Enables / disables DHCP client (0)
        DIGIFLAG        Controls digipeating (7)
        DIGIPORT        Port to digipeat on (this port)
        DYNDNS          Enable / disable Dynamic DNS update client
        ENDPORT       * Ends port definition block
        EXCLUDE         List of callsigns not allowed to connect
        FEC             Enable / disable Forward Error Correction (0)
        FRACK           AX25 Frame Acknowledgement time ms (7000)
        FULLDUP         Allow simultaneous TX/RX (SCC only)
        ID            * Text to identify port on ports display
        IDPATH          Dest & digi path for ID beacons ("ID")
        IDTEXT          Port override for global IDTEXT
        INITSTR         Modem initialisation string (modem only)
        INTERFACENUM  * Interface number this port is bound to
        INTERLOCK       Prevents simultaneous TX on SCC cards
        IPADDRESS       Port override for global IP address
        IPLINK          IP address / hostname of AXIP/AXUDP peer
        MAXFRAME        Max outstanding AX25 L2 frames (3)
        MAXHOPS         Port override for global MAXHOPS
        MAXTT           Port override for global MAXTT
        MHEARD          Enable / disable MHeard on this port
        MHFLAGS         Controls contents of MHeard list (255)
        MINQUAL         Port override for global MINQUAL
        MINTXQUAL       Min NetRom quality to broadcast
        NETMASK         Subnet mask used with IPADDRESS
        NODESINTERVAL   Port override for global NODESINTERVAL
        PACLEN          Port override for global PACLEN
        PERSIST         Probability to transmit 0-255 (64)
        PIPE            Creates a "frame pipe" to another port
        PIPEFLAG        Controls frame piping (3)
        PMSALIAS        Port override for global PMSALIAS
        PMSCALL         Port override for global PMSCALL
        PORTALIAS       Port override for global NODEALIAS
        PORTALIAS2      Secondary alias for digipeating only.
        PORTCALL        Port override for global NODECALL
        PROXY           NetRom systems to tunnel AX25 to
        QUALITY         Default NetRom neighbour quality (10)
        RESPTIME        AX25 delayed ack timer in ms (2000)
        RETRIES         Max connect/disconnect/resent attempts (10)
        RFBAUDS         RF baud rate (1200)
        SESSLIMIT       Max simultaneous connections per user (255)
        SLOTTIME        CSMA interval timer (millisecs) (100)
        SOFTDCD         Use software DCD (SCC only) (0)
        SYSOP           If 1, all users on this port are sysops (0)
        TXDELAY         Delay (ms) between PTT and start of data (300)
        TXPORT          Port on which to TX if not this one (0)
        TXTAIL          Delay (ms) between data end and PTT drop (100)
        UDPLOCAL        RX UDP port for AXUDP operations (93)
        UDPREMOTE       TX UDP port / Partners AXUDP RX port (93)
        UNPROTO         Dest & digi calls for unproto broadcasts
        USERS           Max simultaneous users on this port (255)
        VALIDCALLS      Only these callsigns allowed to connect.

Port Keywords - Detail

APPLMASK

Used only if XRPi is hosting applications, e.g. via the DEDHOST interface. Controls which applications are directly connectible on a given port. The default is 255, which allows all applications. The value is made up by adding together the desired selection from the following numbers:

	1    - Enable Application 1
	2    - Enable Application 2
	4    - Enable Application 3
	8    - Enable Application 4
	16   - Enable Application 5
	32   - Enable Application 6
	64   - Enable Application 7
	128  - Enable Application 8

For example, if a port's definition contains "APPLMASK=9", it will only allow direct connections to applications 1 and 4 on that port, and only if those applications have either an APPLCALL or an APPLALIAS.

APRSPATH

Default digipeater path for APRS frames originated by APRS messaging shell and IGATE. If you omit this, the frames will be sent without any digipeaters. Messaging shell users may override this path.

Example: APRSPATH=RELAY

BCAST

List of destinations for "UI broadcasting". Received non-digipeater UI frames, addressed to one of these destinations, will be re-broadcasted on all ports which have a matching address in their BCAST list, e.g. to broadcast mail beacons from a BBS on one port onto several other ports.

The callsigns must be separated by commas and there should be no spaces in the list.

Example: BCAST=MAIL,ALL

BCFROM

Specifies a list of callsigns who may use the UI broadcast facility (see BCAST). BCFROM applies only to frames *directly* received on the port for which it is specified (i.e. not via digipeaters).

If you wish to restrict the broadcast facility to certain senders only, list the callsigns here. If no calls are specified, the facility is unrestricted. Separate the calls by commas, and don't include any spaces in the list.

Example: BCFROM=GB7PZT,GB7MAX

CFLAGS

Controls whether or not AX25 level 2 uplinking and/or downlinking is allowed on the port. A typical use may be to prevent users from uplinking and downlinking on APRS-only ports. It also allows the sysop to control whether or not L3RTT frames are generated on inter-node links, and whether or not AX25 level 2 fragmentation is allowed on the port.

Add together the decimal values of the desired options from this list:

	Bit Dec   Function
	---------------------------------------------------------
	 0   1  - Allow incoming connections (uplinks).
	 1   2  - Allow outgoing connections (downlinks).
	 2   4  - Applications may downlink unconditionally.
	 3   8  - Suppress L3RTT generation.
	 4  16  - Allow L2 fragmentation.

The default value is 3, i.e. unconditional use of the port.

Irrespective of the setting of CFLAGS, the Sysop can always downlink.

Bit 2 allows applications to downlink unconditionally, i.e. even if users are prevented from downlinking.

Bit 3 was provided to keep the Luddites happy, but its use is strongly deprecated. Setting this flag prevents L3RTT frames from being originated by the port if it is carrying an inter-node link. It will not prevent XRPi from trying to hold inter-node links open, as that is too much of a retrograde step! This bit is not set by default. Note that L3RTT may also be suppressed if a route's MAXTT is 65535.

Bit 4 allows AX25 layer 2 fragmentation if it is set. This is required if Forward Error Correction (FEC) is in use, to allow big L3 frames to be sent.

Examples:

	CFLAGS=2  - Allow downlinking only
	CFLAGS=5  - Allow only sysops and apps to downlink.

CHANNEL

Channel to use on interface (A-P), required only on certain types of multi-channel interface, e.g. KISS. Not required on AXIP, AXUDP, or AXTCP interfaces. Default is A.

Example: CHANNEL=C

CHATALIAS

Port override for global CHATALIAS. If specified, the chat server will use this alias instead of the global CHATALIAS, on this port only.

Example: CHATALIAS=KDRCH2

CHATCALL

Port override for global CHATCALL. If specified, the chat server will use this callsign instead of the global CHATCALL, on this port only.

Example: CHATCALL=G8PZT-9

CWID

Text to send in CW every 30', used only by SCC ports. It specifies a callsign (8 characters max.) which will be sent every 30 minutes using Morse code. If omitted, no cwid is sent.

Example: CWID=G8PZT

DHCP

Specifies whether or not the port IP address will be obtained dynamically using DHCP (DHCP=1) or specified statically (DHCP=0). Default is 0.

DIGIFLAG

Controls digipeating (0=none, default=7). Options are enabled by adding together the following numbers:

	Bit Value Option
        ---------------------------------------------------
         0    1   Digipeat UI frames
         1    2   Digipeat non-UI frames
         2    4   Enable RELAY generic digipeating (deprecated).
         3    8   Enable TRACE generic digipeating (deprecated).
         4   16   Enable WIDE generic digipeating (deprecated).
         5   32   Allow APRS 3rd party digi via L4.
         6   64   Allow digipeating to Internet (IGate).
         7  128   Allow digipeating from Internet (IGate).
         8  256   Enable UITRACE digipeating (e.g. WIDEn-n)
         9  512   Enable UIFLOOD digipeating (e.g. GBRn-n)

Example: DIGIFLAG=5 ; all UI + RELAY generic.

See APRS digipeating....

DIGIPORT

Specifies the port on which digipeated frames are transmitted. Default is 0, i.e. the current port.

Example: DIGIPORT=3 ; Digipeat onto port 3

DYNDNS

Enable / disable Dynamic DNS update client.

ENDPORT *

Marks the end of the PORT definition block. Subsequent keywords will be interpreted as GLOBAL.

EXCLUDE

EXCLUDE specifies a list of one or more callsigns from whom AX25 L2 frames will be ignored. It would typically be used on a user-access port to prevent connections from trouble-makers and pirates. Separate callsigns with commas, and don't include any spaces.

Example: EXCLUDE=NOCALL,P1RAT ; Ignore these users

FEC

Enable / disable Forward Error Correction. In order to make use of FEC, the port needs to be using a KISS TNC with the CRC check disabled (PASSALL ON), or an SCC or YAM card. The default is 0, i.e. disabled.

FRACK

AX25 "T1" timer, i.e. frame acknowledgement time, in milliseconds. Default is 7000.

After sending an AX25 packet, this is the amount of time XRPi will wait for an "ack" before considering the packet to be lost.

The T1 timer starts when the link layer dispatches the packet to the MAC (Media Access Control) layer, so you must allow at least enough time for (MAXFRAME * PACLEN) packets to be sent, plus an ack packet to be received, plus the other end's RESPTIME, plus both end's TXDELAYs, plus a generous allowance for channel congestion.

A frack no less than 7000 millisecs is recommended for average 1200 baud links. Setting this figure too low is antisocial, achieves nothing, and could result in the link retrying out.

However, on fast, wired (e.g. AXUDP) links, 7 secs is excessive, and a figure more like 2000 (2 secs) should be used.

Example: FRACK=7000 ; 7 seconds

FULLDUP

Allow simultaneous TX/RX (SCC only). If you set FULLDUP=1, XRPi will transmit whenever it needs to, without waiting for the other end to stop.

Used only by hardware which is capable of simultaneous transmission and reception, such as full duplex radio or wire links. Default is 0 (simplex / half duplex).

Example: FULLDUP=1 ; Full duplex

ID *

Mandatory text to identify port on "PORTS" display. May contain spaces. Please make it informative.

Example: ID=144.825 MHz 9k6 TCP/IP users

IDPATH

Specifies the destination and digipeater path for ID beacons.

The default AX25 destination and path is "ID" with no digipeaters. You may wish to modify this, for example on APRS ports, to digipeat your beacon.

Example: IDPATH=APRS,RELAY,WIDE

IDTEXT

Optional ID text to use, instead of global IDTEXT, on this port only (e.g. for APRS ports). Only one line of text (248 characters max.) may be specified.

Example: IDTEXT=!5224.00N/00215.00W# (Kidder)

INITSTR

Modem initialisation string (MODEM ports only). This is a string of characters which will be sent to the modem when Xrouter is started.

Example: INITSTR=ATM0

INTERFACENUM *

Interface number this port is bound (attached) to. This directive is mandatory.

INTERLOCK

Used only by SCC cards, because KISS TNC's make their own decisions about when to transmit, and XRPi has no control over that process.

If a non-zero INTERLOCK value is specified, no two ports with the same value will transmit at the same time. Default=0.

Example: INTERLOCK=4

IPADDRESS

Port override for global IP address. If this is specified, it will be used instead of the global IP address for all TCP/IP operations on this port.

Example: IPADDRESS=44.131.91.5

IPLINK

IP address or hostname of AXIP or AXUDP link partner (AXIP and AXUDP ports only).

If the partner has a static IP address, it is more efficient to use the IP address here, otherwise it is necessary to use the hostname.

Examples:

	IPLINK=62.51.67.21
	IPLINK=gb7pzt.dyndns.org

MAXFRAME

Specifies the maximum number of frames XRPi will send to an AX25 partner before it must wait for an ack. The normal range is between 1 and 7, although maxframes of up to 127 are allowed on modulo-128 links. The default value of MAXFRAME is 3.

If you set a value between 8 and 63, XRPi will attempt to use Modulo-128 (Extended AX25) on outgoing links. If the link partner is not capable of Modulo-128, the link will fall-back to normal AX25.

If the port PACLEN is set to 0, XRPi dynamicallys adapts MAXFRAME (and PACLEN) to the link conditions, to maximise throughput.

Example: MAXFRAME=4

MAXHOPS

Specifies the maximum accepted hop count for new nodes table entries received via INP3 unicasts from neighbours on this port. Node information with hop counts that exceed this figure are not accepted into the nodes table. This parameter has no effect on data received via conventional NetRom nodes broadcasts.

MAXHOPS would typically be used to limit the "hop horizon" to a smaller value than the default horizon, which is 30. Like MAXTT, it can be used to limit the number of node entries that are accepted via a particular port or neighbour.

It can be overridden for individual routes using by "locking-in" the route at the end of XROUTER.CFG, or by a ROUTE ADD command in the XRNODES file or at the command prompt. Defaults to global MAXHOPS.

MAXTT

Specifies the maximum accepted "trip time" (transit time) for new nodes table entries received via INP3 unicasts from neighbours on this port.

Node information with trip times that exceed this figure are not accepted into the nodes table. This parameter has no effect on data received via conventional NetRom nodes broadcasts.

MAXTT would typically be used to limit the "trip time horizon" to a smaller value than the default horizon, which is 60000 (600 seconds). Like MAXHOPS, it can be used to limit the number of node entries that are accepted via a particular port or neighbour.

It can be overridden for individual routes using by "locking-in" the route at the end of XROUTER.CFG, or by a ROUTE ADD command in the XRNODES file or at the command prompt. Defaults to global MAXTT.

MHEARD

Enable/disable the MHEARD function on this port. The number specifies how many callsigns to maintain in the list. Set to 0 to disable MHEARD. Default is 15 calls.

Example: MHEARD=10 ; Mheard enabled, 10 calls

MHFLAGS

Controls which callsigns are recorded in the MHeard list, and defaults to 255 (record everything). The argument is the sum of the required options from this list:

	1    Show directly heard stations
	2    Show directly heard digipeaters
	4    Show digipeated stations

Example: MHFLAGS=1 ; show directly heard stations only

MINQUAL

Minimum Net/rom quality to add to node table for nodes received via this port. Defaults to global MINQUAL.

Within nodes broadcasts received on that port, any node whose quality (after derating by port QUALITY) is less than the minqual will not be accepted into the nodes table.

If specified, this overrides the global minqual, and can be used to exclude unreachable and marginal nodes.

Example: MINQUAL=100 ; No nodes less than quality 100

MINTXQUAL

Minimum NetRom node quality to include in nodes broadcasts on this port. Range 0 to 255, Default is 0. This is used to limit the size of nodes broadcasts on ports which are low bandwidth, low quality, or where the neighbours have limited nodes table capacity.

Example: MINTXQUAL=100 ; Don't broadcast nodes with quality <100

NETMASK

Subnet mask used with IPADDRESS to specify which IP addresses are on the same network segment, and can be reached directly. For more information see the NETMASK command page.

NODESINTERVAL

Interval, in minutes, between NetRom nodes broadcasts on this port only. Defaults to global NODESINTERVAL.

Whilst the Netrom network usually works on a 60 minute broadcast cycle, some types of software insist on a much smaller broadcast interval.

It would be harmful to the established network if sysops tried to accommodate these neighbours by setting the global NODESINTERVAL to a smaller value, but using this keyword on a per-port basis you can keep these neighbours happy without disrupting the rest of the Netrom network.

If you set NODESINTERVAL=0, XRPi will ignore received nodes broadcasts on this port, but will allow L3/L4 activity if QUALITY is non-zero. Example: NODESINTERVAL=10 ; 10 minues between broadcasts

PACLEN

Specifies the maximum length of the information-bearing portion of ax25 packets transmitted on this port only. If not specified, it defaults to the global PACLEN.

All frames originating at XRPi use the global or port paclens specified, but Netrom frames originating at other systems can not be fragmented, so we have no control over them, and they may be larger than our paclen.

If the port PACLEN is set to 0, Xrouter will dynamically adapt PACLEN (and MAXFRAME) to the link conditions, to maximise throughput. Example: PACLEN=160 ; Allow 160 byte packets on this port

PERSIST

PERSIST is the AX25 "Probability to transmit" in a given time slot (see SLOTTIME), used to minimise media contention.

Persist should be set to (255 / (no. of users on channel)), e.g. for a channel with an average of 10 users on at any one time you would set Persist to 25. Default is 64.

PIPE

Creates a "frame pipe" to another port. This allows frames received (and optionally sent) on this port to be copied to another port, e.g. to allow a PMS on one port to see the traffic on another port.

Unless the "bi-directional" option (see below) is specified, pipes are one way. In order to have two way traffic using a uni-directional pipe, you must set up a reverse pipe on the opposite port.

You may pipe several ports to a single destination port, but you can only have one *outgoing* pipe from any port.

Pipes are capable of generating an immense amount of traffic, so use them with care - your target port MUST be capable of handling the traffic load.

By default, pipes are not selective, i.e. they pass traffic from any source callsign to any destination callsign (with the exception of Budlisted callsigns). On a busy channel, this could result in a lot of unnecessary traffic being piped.

Pipes can be made "selective", by adding a comma-delimited callsign list, e.g. "PIPE=4 GB7PZT,KDRBBS". This will reduce the loading on the target port, by piping only the frames with the specified calls in the destination field.

Pipes can also be made selective in terms of the types of traffic they pipe (AX25, NetRom etc). This is controlled by PIPEFLAG (see below).

Pipes can be made "bi-directional" by adding 512 to the PIPEFLAG value (see below: suggested value = 515). If a frame is piped on a bi-directional pipe, the source call is remembered so that responses will be piped back to the sender. Thus a reverse pipe is not needed.

Bi-directional pipes are useful where a BBS has a front end router - simply set up bi-directional selective pipes from each user port to the BBS port, and set up the BCAST option so that the UI mail headers are broadcast on each user port. The BBS will then allow direct connect and will respond to resync requests.

To disable piping, set PIPE=0 or just omit the command.

Example: PIPE=2 ; Pipe frames from this port to port 2

PIPEFLAG

PIPEFLAG is only used when piping is active, and controls which frames are piped. The default is 3. The argument is the sum of the required options as follows:

	1    - UI frames *not* addressed to nodecall/alias.
	2    - Non-UI frames *not* addressed to nodecall/alias.
	4    - UI frames addressed to nodecall/alias.
	8    - Non-UI frames addressed to nodecall/alias.
	16   - UI frames transmitted by XRPi.
	32   - Non-UI frames transmitted by XRPi.
	64   - Allow budlisted users to be piped.
	128  - Netrom frames
	256  - IP / ARP frames
	512  - Bi-directional piping

Example: PIPEFLAG=5 ; Pipe received UI frames only

PMSALIAS

Port override for global PMSALIAS

PMSCALL

Port override for global PMSCALL

PORTALIAS

Specifies an AX25 alias for this port, to be used in addition to the NODEALIAS.

Example: PORTALIAS=KDRMIN

PORTALIAS2

Secondary alias for digipeating only. This callsign does not accept connections.

PORTCALL

Specifies an AX25 callsign to use on this port, in addition to the NODECALL.

Example: PORTCALL=G8PZT-1

PROXY

Remote NetRom systems to whom we will tunnel AX25 L2 frames. (See PROXIES page for full explanation)

Example: PROXY=GB7PZT,GB7BBS

QUALITY

Default quality for nodes whose broadcasts are received on this port (default=10). Setting this to 0 disables all NetRom L3/4 activity on this port.

Example: QUALITY=30

RESPTIME

AX25 "T2" (delayed ack) timer in milliseconds, i.e. the time to wait after receiving a frame before sending an ack. This allows multi-frame transmissions to be acknowledged with a single ack, increasing link efficiency.

Resptime should be long enough for a link partner to transmit a full-sized information frame, i.e. approximately ((their_paclen * 10000) / RFbauds) millisecs, otherwise you will send unnecessary ack frames.

Too high a value will cause the link to be too "relaxed", whereas too low a value will cause too many acks. Both extremes reduce the link efficiency.

1500 (default) is OK for 1200 bauds with paclen=120, but 2200 would be more appropriate if their paclen was 256. At 9600 baud, or on AXUDP links, 200 millisecs is probably adequate.

Example: RESPTIME=2000 ; 2 seconds

RETRIES

AX25 maximum consecutive connect / disconnect / resend attempts (default = 10).

There is little point in setting retries more than 10, other than for test purposes. If you need so many retries it's a useless link and you're just wasting everyone else's airtime. The higher you set this value, the longer users will have to wait to get a "failure with" for a non-contactable destination.

Example: RETRIES=5

RFBAUDS

RF baud rate (default = 1200).

This parameter is used with "real" tnc's and YAM modems attached via RS232, because the RF baud rate is usually different to the RS232 baud rate. It simply helps XRPi make timing decisions (such as nodes broadcast inter-packet timing) and report certain stats correctly.

Example: RFBAUDS=2400

SESSLIMIT

Sesslimit specifies the maximum simultaneous connects each user is allowed on this port. Default is 255. This would typically be used to "choke" users who hog all the bandwidth on a port with too many connections.

Example: SESSLIMIT=5

SLOTTIME

CSMA interval timer (millisecs), used with PERSIST to make channel access decisions (default=100).

If the channel is clear, the TNC (or SCC/YAM card) will generate a random number which is then compared with the PERSIST value. If it is less than PERSIST, the TNC will wait for the SLOTTIME interval, then repeat the action, otherwise it will transmit immediately.

This improves throughput by ensuring that everyone doesn't transmit as soon as the channel is clear, which would cause collisions and retries.

Example: SLOTTIME=100 ; 100 millisecs per slot

SOFTDCD

Softdcd is used only by SCC cards and defaults to 0.

If SOFTDCD=1 the real dcd will be ignored, and the SCC driver will use the presence of HDLC data as a DCD indication.

Using SOFTDCD=1 with an open squelch generates a *huge* interrupt loading, which may cause degradation of performance, depending on the PC type, so it is not recommended.

Example: SOFTDCD=0

SYSOP

If you set SYSOP=1, all users who connect on this port will get full sysop status without needing to answer a password challenge. This is intended ONLY FOR USE ON SECURE LINKS, such as RS232 or Ethernet, and the default is zero.

TXDELAY

Transmit keyup delay in milliseconds (default=300).

After keying the transmitter, the TNC (or SCC / YAM card) will wait for this interval before sending HDLC data. This allows the TX to stabilise and the partner's squelch to open.

Example: TXDELAY=500 ; Synthesiser is slow to lock

TXPORT

Port to transmit on (default = 0 = this port).

You would typically use this when several ports share a single transmitter, with separate receivers.

Example: TXPORT=5 ; Transmit on port 5

TXTAIL

TX keydown delay in milliseconds (default = 100).

This is the interval, after sending a frame, for which the transmitter remains active. It is intended to allow CRC and closing flags to be sent. It has no meaning on non-radio ports.

Due to PC timing inaccuracies, you should set this no lower than 100 for SCC cards!

Example: TXTAIL=100

UDPLOCAL

The UDP port number for the local end of an AXUDP link. Used only by AXUDP ports. Default is 93. This number must match the link partner's UDPREMOTE, i.e. the destination service number in the frames from him to you.

It is perfectly valid for all your ports to use the same UDPLOCAL. This reduces the number of "holes" (port forwards) you need to make in your firewall. The *only* reason ever to change UDPLOCAL from the default is when you have more than one AXUDP node sharing the same public IP address. Your link partners have no right to dictate this value!

Example: UDPLOCAL=7388

UDPREMOTE

The UDP destination number in the AXUDP frames from you to your link partner. It must match the link partner's UDPLOCAL, otherwise the link will not function.

If not specified, UDPREMOTE defaults to 93. It is only used on AXUDP ports.

You have no right to dictate this value to your link partner. It is THEIR choice only (see UDPLOCAL).

Example: UDPREMOTE=10093

UNPROTO

Destination callsign and optional digipeater string used for unproto broadcasts from applications on this port. Separate the callsigns with commas.

Example: UNPROTO=CQ,G6YAK

USERS

Maximum no. of simultaneous users on this port. Default is 255 which means "no limit".

Example: USERS=9

VALIDCALLS

Validcalls allows AX25 frames only from the specified callsigns (opposite of EXCLUDE), and is typically used to prevent users from connecting to link-only ports. Callsigns must be separated by commas, with no spaces.

Example: VALIDCALLS=G6YAK,G6AMU ; Accept only these users

Example Ports

a) KISS Port, no NetRom, Pipe to port 7:

User-access frequency, hence NetRom linking is suppressed by zero QUALITY. Note the bi-directonal selective UI pipe to a BBS which is on port 7, allowing FBB resync requests, and the use of BCAST for broadcasting the BBS's mail beacons onto this port.

	PORT=1
		ID=144.850 MHz 1200 baud users
		INTERFACENUM=1	; Multi-drop KISS interface
		CHANNEL=C	; 3rd TNC
		PACLEN=160	; Larger than default
		MAXFRAME=2	; Smalled than default
		TXDELAY=400	; Synth rig takes time to tx
		QUALITY=0	; Disable NetRom on this port
		BCAST=MAIL	; Allow mail beacons from BBS
		BCFROM=GB7PZT	; BBS call allowed to Bcast
		PIPE=7 GB7PZT	; Selective pipe to BBS
		PIPEFLAG=513	; Bi-directional, UI-only
	ENDPORT

b) APRS-only port:

Note the use of comment lines, an alternate IDTEXT, and the use of CFLAGS to disable connected mode operations, thus MAXFRAME,FRACK,PACLEN etc. are not needed.

	PORT=13
		ID=144.800 MHz 1200 baud APRS
		INTERFACENUM=1	; Multidrop KISS interface
		CHANNEL=B	; 2nd TNC
		CFLAGS=0	; Prevent up/downlinks on this port
		DIGIFLAG=5	; Digi only UI frames addressed via RELAY
		MHEARD=22	; Nice big MH list
		IDTEXT=!5224.00N/00215.00W#PHG3021 Kidderminster APRS digi
	;
	;       Override default destination & path for ID beacons
	;
		IDPATH=APRS,RELAY,WIDE
	;
	;       Default digipeater path for APRS frames originated by APRS
	;       messaging shell and Igate. If you omit this, the frames will
	;       be sent without any digipeaters. Messaging shell users may
	;	override this path.
		
		APRSPATH=RELAY
		
	ENDPORT

c) AXIP Port:

Note the use of lower FRACK and RESPTIME because it is a faster link.

	PORT=8
		ID=AXIP link with WA3IP
		INTERFACENUM=2	; Points to an AXIP interface
		IPLINK=55.73.88.69
		FRACK=2000
		RESPTIME=200
	ENDPORT

d) AXUDP Port:

Illustrates the use of non-standard UDPLOCAL and UDPREMOTE, a hostname for IPLINK, plus lower FRACK and RESPTIME because it is a fast link.

      PORT=9
		ID=AXUDP link with VK1UDP
		INTERFACENUM=3	; AXUDP interface
		IPLINK=vk1udp.ath.cx
		UDPLOCAL=9393	; Non-standard
		UDPREMOTE=10093	; Non-standard
		FRACK=2000
		RESPTIME=200
	ENDPORT