GateD Configuration Guide - Config Intro

# 6.1 Configuration Overview

## 6.1.1 Introduction to Configuring GateD

### A) Syntax

The GateD config file consists of a sequence of statements terminated by a semi-colon (``;`'). Statements are composed of tokens separated by white space, which can be any combination of blanks, tabs and newlines. This structure simplifies identification of the parts of the configuration associated with each other and with specific protocols. Comments may be specified in either of two forms. One form begins with a pound sign (``#`') and runs to the end of the line. The other form, C style, starts with a `/*' and continues until it reaches `*/'.

Keywords and special characters that the parser expects exactly are displayed using the HTML strong style. Parameters are specifying in the HTML variable definition style. Parameters shown in square brackets (``[`' and ``]`') are used to show optional keywords and parameters. The vertical bar (``|`') is used to indicate between a choice of optional parameters. Parentheses (``(`' and ``)`') are used to group keywords and parameters when necessary.

For example, in the syntax description:

        [ backbone | ( area area ) ]

The square brackets say that either parameter is optional. The keywords are backbone and area. The vertical bar indicates that either ``backbone'' or ``area area'' may be specified. Since area is in the variable definition style, it is a parameter that needs to be provided.

### B) Statement Grouping

The configuration statements and the order in which these statements appear divide gated.conf into options statements, interface statements, definition statements, unicast and multicastprotocol statements, static statements, control statements, and aggregate statements. Entering a statement out of order causes an error when parsing the configuration file.

Two other types of statements do not fit in these categories: %directive statements and %tracestatements. These statements provide instructions to the parser and control tracing from the configuration file. They do not relate to the configuration of any protocol and may occur anywhere in the gated.conf file.

#### C) Route Preference and Selecting a Route

Preference is the value GateD uses to order preference of routes from one protocol or peer over another. Preference can be set in the GateD configuration files in several different configuration statements. Preference can be set based on network interface over another, from one protocol over another, or from one remote gateway over another. BGP selects the best path to an AS from all the known paths and propagates the selected path to its neighbors. GateD uses certain criteria, in a certain order, to select the best path.

#### D) Statement Summary

A summary table of the configuration statements (in the configuration statement summary) lists each GateD config statement by name, identifies the statement type, and provides a short synopsis of the command's function. More detailed definitions and descriptions of each of the eight classes of GateD statements follow in separate sections.

Last updated April 25, 1997