atalk.local(5)

NAME
atalk.local - configuration file for CAP.

DESCRIPTION
atalk.local contains the static configuration information needed to run the CAP system with IPTalk (See CAP(8)). This document defines the permissible contents of atalk.local for this distribution.

The version of CAP that supports Ethertalk uses another file called etalk.local. The contents of etalk.local are "free format" with keyword identifiers for each piece of information. The file is written by both UAB and the Native Ethertalk AARP daemon aarpd after they have identified the network, node and zone name. Refer to etalk.local(5) and UAB(8) for more information. If atalk.local exists, it is used to "seed" values that are not otherwise obtained from the network.

Unlike LocalTalk and EtherTalk hosts, IPTalk based CAP hosts do not dynamically establish their AppleTalk addresses, zones, or the network's AppleTalk bridge. The primary function of atalk.local is to define these values.

The format of the file for IPTalk is quite simple. There are two significant lines in the file, and two extra lines which are optional (the third line is mandatory if the fourth line is used). There may also be any number of comment lines, which are identified by an initial pound sign (#) character. The first significant line defines the AppleTalk address of the host. The second line defines which AppleTalk Bridge to use. This bridge must be running software that supports the IPTalk (KIP) encapsulation. For example:
	# host's AppleTalk network, node, zone
	55.1	6	"MY ZONE"
	# bridge's AppleTalk network, node, and IP address
	55.1	5	128.254.1.5
A network number can be specified as a single number or as two bytes separated by a "." (as above).

IMPORTANTNOTE: An underscore in the zone name is no longer treated as a space as in previous versions. If a space in a zone name is desired, then use double or single forward (" or ') quotes to surround the name, as in the example shown above. This is the same convention used by later versions of atalkad. To have a quote in the zone name, escape it with a backslash (\).

OPTIONAL LINES
atalk.local may have up to two more (non comment) lines. The third line describes the network and node number for the NIS information server. That is, the network and node numbers for the host that is running atis, see atis(8). If this line is not present, the network and node numbers are taken from the first (host) line.

The optional fourth line (meaning you MUST HAVE a NIS entry) specifies the network and zone name for Asynchronous AppleTalk running on this host. Async AppleTalk allows connection to AppleTalk networks via serial lines connected to UNIX hosts. The entry specifies a Network number and Zone name that belong to this host only and must match the 'A' entries in atalkatab (using atalkad 1.23 or later available via FTP from munnari.OZ.AU). This service is currently only available with a Webster MultiPort Gateway, Shiva FastPath (early 1991) and when CAP is used with UAB.

A fully qualified atalk.local would therefore look like this.

	# host's AppleTalk network, node, zone
	55.1	6	"MY ZONE"
	# bridge's AppleTalk network, node, and IP address
	55.1	5	128.254.1.5
	# name information server network, node
	55.1	6
	# async appletalk network and zone
	170.32	"Async Zone"

The contents of atalk.local for IPtalk follow rigidly from what is defined in atalkad's atalkatab file. Remember that atalkatab defines mappings for IP subnets to AppleTalk networks. The host's appletalk network number must set as one of those mappings for the subnet that the host is on. In addition, the zone name specified in atalk.local must be the zone name of the appletalk network specified. The host's node number must be the last byte of the host's ip network number. For more information on why this is necessary, see the section on IPTalk routing below.

The AppleTalk bridge information comes from the anete network number in atalkatab. The anete network number is the one specified in the bridge's configuration for the UDP encapsulated "interface". When using the anete network number for the bridge, its AppleTalk node number MUST EQUAL the last byte of its IP address.

The overall combination of the Async AppleTalk UNIX code and the specified bridge form the "pseudo" Async AppleTalk bridge.

IPTalk ROUTING
Appletalk bridges that implement IPtalk route to UDP encapsulated networks by using the AppleTalk to IP mappings (N[0123] and "H" flagged lines) defined in atalkatab to go from AppleTalk network numbers to IP network numbers and vice versa. Of particular interest is that it assumes that the IP address of a host can be found by replacing the last byte of the IP address defined in the mapping with the DDP node number. (Remember, KIP encapsulates DDP packets not LAP packets). This has two major consequences. First, the node numbers of KIP/CAP hosts must be the same as the last byte of their IP network numbers.

Second, Appletalk to IP network mappings are expected to cover subnets (8 bit subnets for Class B networks, 16 bit for Class A networks). For the purposes of routing, it does not matter how your IP networks are really subnetted (or not subnetted). However, the mapping also defines a second piece of information. It tells how to broadcast NBP lookup requests to all hosts on a particular UDP capsulated Appletalk network and the underlying IP network structure is of importance here. Unfortunately, the details of this issue are beyond the scope of this document.

FILES
atalk.local usually resides in /etc

BUGS
The node numbers should be automatically determined since they are fixed. In addition, it would be nice if the zone name were picked up automatically as well.

SEE ALSO
KIP documentation
CAP(3), CAP(8), atalkatab(5), atalkad(8), atis(8)