NAME

pathalias − electronic address router

SYNOPSIS

pathalias [ −icv ] [ −l host ] [ −d arg ] [ −t arg ] [ files ]

DESCRIPTION

Pathalias computes the shortest paths and corresponding routes from one host (computer system) to all other known, reachable hosts.  Pathalias reads host-to-host connectivity information on standard input or in the named files, and writes a list of host-route pairs on the standard output.

Options are:

−i Ignore case:  map all host names to lowercase.  By default, case is significant. 

−c Print costs: print the path cost (see below) before each host-route pair. 

−v Verbose: report some statistics on the standard error output. 

−l host
Set local host name to host. By default, pathalias discovers the local host name in a system-dependent way. 

−d arg
Declare a dead link, host, or network (see below). If arg is of the form “host1!host2,” the link from host1 to host2 is treated as an extremely high cost (i.e., DEAD) link.  If arg is a single host name, that host is treated as dead and is used as an intermediate host of last resort on any path.  If arg is a network name, the network requires a gateway. 

−t arg
Trace input for link, host or network on the standard error output. The form of arg is as above. 

The public domain version of pathalias includes two undocumented options, that are briefly described in the Special Options section below. 

Input Format

A line beginning with white space continues the preceding line.  Anything following ‘#’ on an input line is ignored. 

A list of host-to-host connections consists of a “from” host in column 1, followed by white space, followed by a comma-separated list of “to’ hosts, called links. A link may be preceded or followed by a network character to use in the route. Valid network characters are ‘!’ (default), ‘@’, ‘:’, and ‘%’. A link (and network character, if present) may be followed by a “cost” enclosed in parentheses. Costs may be arbitrary arithmetic expressions involving numbers, parentheses, ‘+’, ‘−’, ‘*’, and ‘/’. The following symbolic costs are recognized:

LOCAL25(local-area network connection)
DEDICATED95(high speed dedicated link)
DIRECT200(toll-free call)
DEMAND300(long-distance call)
HOURLY500(hourly poll)
EVENING1800(time restricted call)
DAILY5000(daily poll, also called POLLED)
WEEKLY30000(irregular poll)

In addition, DEAD is a very large number (effectively infinite), and HIGH and LOW are −5 and +5 respectively, for baud-rate or quality bonuses/penalties.  These symbolic costs represent an imperfect measure of bandwidth, monetary cost, and frequency of connections.  For most mail traffic, it is important to minimize the number of intermediaries in a route, thus, e.g., HOURLY is far greater than DAILY / 24.  If no cost is given, a default of 4000 is used. 

For the most part, arithmetic expressions that mix symbolic constants other than HIGH and LOW make no sense.  For example, if a host calls a local neighbor whenever there is work, and additionally polls every evening, the cost is DIRECT, not DIRECT+EVENING. 

Some examples:

downprinceton!(DEDICATED), tilt,
%thrash(LOCAL)
princetontopaz!(DEMAND+LOW)
topaz@rutgers(LOCAL)

If a link is encountered more than once, the least-cost occurrence dictates the cost and network character.  Links are treated as bidirectional, to the extent that a DEAD reverse link is assumed unless better information is available. 

The set of names by which a host is known by its neighbors is called its aliases. Aliases are declared as follows:

name = alias, alias ... 

The name used in the route to or through aliased hosts is the name by which the host is known to its predecessor in the route. 

Fully connected networks, such as the ARPANET or a local-area network, are declared as follows:

net = {host, host, ...}

The host-list may be preceded or followed by a routing character, and may be followed by a cost:

princeton-ethernet = {down, up, princeton}!(LOCAL)
ARPA = @{sri-unix, mit-ai, su-score}(DEDICATED)

The routing character used in a route to a network member is the one encountered when “entering” the network.  See also the sections on gateways and domains.

Connection data may be given while hiding host names by declaring

private {host, host, ...}

Pathalias will not generate routes for private hosts, but may produce routes through them.  The scope of a private declaration extends from the declaration to the end of the input file in which it appears.  It is best to put private declarations at the beginning of the appropriate input file. 

Output Format

A list of host-route pairs is written to the standard output, where route is a string appropriate for use with printf(3S), e.g.,

rutgersprinceton!topaz!%s@rutgers

The “%s” in the route string should be replaced by the user name at the destination host.  (This task is normally performed by a mailer.) 

Except for domains (see below), the name of a network is never used in expansions.  Thus, in the earlier example, the path from down to up would be “up!%s,” not “princeton-ethernet!up!%s.”

Gateways

A network is represented by a pseudo-host and a set of network members.  Links from the members to the network have the weight given in the input, while the cost from the network to the members is zero.  If a network is declared dead on the command line (with the −d option), the member-to-network links are marked dead, which discourages paths to members by way of the network. 

If the input also shows a link from a host to the network, then that host will be preferred as a gateway.  Gateways need not be network members. 

For example, suppose CSNET is declared dead on the command line and the input contains

CSNET = {...}
csnet-relayCSNET

Then routes to CSNET hosts will use csnet-relay as a gateway. 

Domains

A host or network whose name begins with ‘.’ is called a domain.  Domains are presumed to require gateways, i.e., they are DEAD.  The route given by a path through a domain is similar to that for a network, but here the domain name is tacked onto the end of the next host.  Subdomains are permitted.  For example,

harvard.EDU
.EDU = {.BERKELEY}
.BERKELEYernie

yields

ernie...!harvard!ernie.BERKELEY.EDU!%s

Output is given for the nearest gateway to a domain, e.g., the example above gives

.EDU...!harvard!%s

Special Options

The public domain version of pathalias includes two undocumented options that rewrite named files with intermediate data of limited usage.  Here are brief descriptions:

−g file Dump graph edges into file in the form "host>host" for simple connections and "host@<tab>host" for network connections (from hosts to networks only). 

−s file Dump shortest path tree into file in the form "host<tab>[@]host[!](cost)", including both connections from hosts to networks and from networks to hosts.  This data may be useful for generating lists of one-way connections. 

BUGS

The −i option should be the default. 

The order of arguments is significant.  In particular, −i and −t should appear early. 

Pathalias can generate hybrid (i.e. ambiguous) routes, which are abhorrent and most certainly should not be given as examples in the manual entry. 

Multiple ‘@’s in routes are prohibited by many mailers, so pathalias resorts to the “magic %” rule when appropriate.  This convention is not documented anywhere, including here. 

AUTHOR

Pathalias was developed by Peter Honeyman and Steven M. Bellovin. 

FILES

newsgroup mod.map Likely location of some input files. 

Hewlett-Packard Company  —  Version B.1,  May 11, 2021