pathalias(8)
NAME
pathalias, makedb, arpatxt - mail routing tools
SYNOPSIS
/usr/lib/smail/pathalias [ -ivcDf ] [ -t link ] [ -l host ] [ -d link ] [
files ... ]
/usr/lib/smail/makedb [ -a ] [ -o dbmfile ] [ files ... ]
/usr/lib/smail/arpatxt [ -@fi ] [ -g gateway ] [ -p privatefile ] [
-d directory ] [ 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.
Here are the pathalias options:
-i Ignore case: map all host names to lower case. By default, case
is significant.
-c Print costs: print the path cost before each host-route pair.
-v Verbose: report some statistics on the standard error output.
-D Terminal domains: see domains section.
-f First hop cost: the printed cost is the cost to the first relay in
a path, instead of the cost of the path itself; implies (and
overrides) the -c option.
-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. If arg is of the form
``host-1!host-2,'' the link from host-1 to host-2 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 a relay 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.
Makedb takes pathalias output and creates or appends to a dbm(3)
database.
Here are the makedb options:
-a Append to an existing database; by default, makedb truncates the
database.
-o dbmfile
Identify the output file base name.
Arpatxt converts the Internet hosts table hosts.txt into pathalias input.
Here are the arpatxt options:
-@ Generate pathalias input that specifies `@' style addressing. The
default is to produce pathalias input that specifies `!' style
addressing.
-f ``Filter mode'' -- write output on stdout. Normally, arpatxt
writes the description of each domain into a separate file.
-i Map output to lower case.
-g arg
Declare a gateway to the Internet or one of its subdomains. If arg
contains one or more dots, the left-hand side component that
contains no dots is declared a gateway to the domain to the right
of the dot. Otherwise, arg is declared a gateway to the Internet
as a whole.
-p privatefile
Privatefile contains a list of host names that conflict with other
names.
-d directory
Write output files in directory.
Pathalias 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 `/'. Negative costs are prohibited. The following
symbolic costs are recognized:
LOCAL 25 (local-area network connection)
DEDICATED 95 (high speed dedicated link)
DIRECT 200 (toll-free call)
DEMAND 300 (long-distance call)
HOURLY 500 (hourly poll)
EVENING 1800 (time restricted call)
DAILY 5000 (daily poll, also called POLLED)
WEEKLY 30000 (irregular poll)
In addition, DEAD is a very large number (effectively infinite), HIGH and
LOW are -5 and +5 respectively, for baud-rate or quality
bonuses/penalties, and FAST is -80, for adjusting costs of links that use
high-speed (9.6 Kbaud or more) modems. 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 hosts in a route, thus, e.g., HOURLY * 24 is much larger than
DAILY. If no cost is given, a default of 4000 is used.
For the most part, arithmetic expressions that mix symbolic constants
other than HIGH, LOW, and FAST make no sense. E.g., 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:
down princeton!(DEDICATED), tilt,
%thrash(LOCAL)
princeton topaz!(DEMAND+LOW)
topaz @rutgers(LOCAL+1)
If a link is encountered more than once, the least-cost occurrence
dictates the cost and network character. Links are treated as
bidirectional but asymmetric: for each link declared in the input, a
DEAD reverse link is assumed.
If the ``to'' host in a link is surrounded by angle brackets, the link is
considered terminal, and further links beyond this one are heavily
penalized. E.g., with input
seismo <research>(10), research(100), ihnp4(10)
research allegra(10)
ihnp4 allegra(50)
the path from seismo to research is direct, but the path from seismo to
allegra uses ihnp4 as a relay, not research.
The set of names by which a host is known to 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 (`!'
default), and may be followed by a cost (default 4000). The network name
is optional; if not given, pathalias makes one up.
etherhosts = {rahway, milan, joliet}!(LOCAL)
ringhosts = @{gimli, alida, almo}(DEDICATED)
= {etherhosts, ringhosts}(0)
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, or to a
private declaration with an empty host list, whichever comes first. The
latter scope rule offers a way to retain the semantics of private
declarations when reading from the standard input.
Dead hosts, links, or networks may be presented in the input stream by
declaring
dead {arg, ...}
where arg has the same form as the argument to the -d option.
To force a specific cost for a link, delete all prior declarations with
delete {host-1!host-2}
and declare the link as desired. To delete a host and all its links, use
delete {host}
Error diagnostics refer to the file in which the error was found. To
alter the file name, use
file {filename}
Fine-tuning is possible by adjusting the weights of all links from a
given host, as in
adjust {host-1, host-2(LOW), host-3(-1)}
If no cost is given a default of 4000 is used.
Input from compressed (and uncompressed) files can be piped into
pathalias with the following script.
for i in $*; do
case $i in
*.Z) echo "file {`expr $i : '(.*).Z'`}
zcat $i ;;
*) echo "file {$i}"
cat $i ;;
esac
echo "private {}"
done
Output Format
A list of host-route pairs is written to the standard output, where route
is a string appropriate for use with printf(3), e.g.,
rutgers princeton!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, the name of a network is never used in routes. 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, the member-to-network links are marked dead, which
effectively prohibits access to the network from its members.
However, if the input also shows an explicit link from any host to the
network, then that host can be used as a gateway. (In particular, the
gateway need not be a network member.)
E.g., if CSNET is declared dead and the input contains
CSNET = {...}
csnet-relay CSNET
then routes to CSNET hosts will use csnet-relay as a gateway.
Domains
A 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.
E.g.,
harvard .EDU # harvard is gateway to .EDU domain
.EDU = {.BERKELEY, .UMICH}
.BERKELEY = {ernie}
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
Output is given for a subdomain if it has a different route than its
parent domain, or if all its ancestor domains are private.
If the -D option is given on the command line, pathalias treats a link
from a domain to a host member of that domain as terminal. This property
extends to host members of subdomains, etc, and discourages routes that
use any domain member as a relay.
Databases
Makedb builds a dbm(3) database from the standard input or from the named
files. Input is expected to be sequence of ASCII records, each
consisting of a key field and a data field separated by a single tab. If
the tab is missing, the data field is assumed to be empty.
FILES ET AL.
/usr/local/lib/palias.{dir,pag} default dbm output
newsgroup comp.mail.maps likely location of some input files
getopt(3), available from comp.sources.unix archives (if not in the C
library).
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. Experienced mappers largely shun `@' when preparing input;
this is historical, but also reflects UUCP's facile syntax for source
routes.
Multiple `@'s in routes are loathsome, so pathalias resorts to the
``magic %'' rule when necessary. This convention is not documented
anywhere, including here.
The -D option elides insignificant routes to domain members. This is
benign, perhaps even beneficial, but confusing, since the behavior is
undocumented and somewhat unpredictable.
SEE ALSO
P. Honeyman and S.M. Bellovin, ``PATHALIAS or The Care and Feeding of
Relative Addresses,'' in Proc. Summer USENIX Conf., Atlanta, 1986.