
Customizing BGP Services
114065 Rev. A 6-23
Configuring a BGP-4 AS Pattern-Matching Policy
In the Bay Networks implementation of AS path pattern matching for Version
10.0, the user must know regular expression syntax. For Version 11.0, we have
provided a simpler syntax. This syntax is defined in
Table 6-3.
IP software passes this simple form of regular expressions to a preprocessor that
expands the simple expression into a generic regular expression.
There are two additional changes in AS pattern matching syntax for Version 11.0.
• AS pattern matching for Version 11.0 uses a new symbol to denote AS path
segments of the type AS_SET. In Version 10.0, AS sets are denoted by the
symbols '`. Beginning with Version 11.0, AS sets are denoted by {}.
• Version 10.0 requires that the user enter a space delimiter after entering the
last AS in an AS pattern matching expression (for example, “555 $”.
Beginning with Version 11.0, the extra space delimeter at the end of an AS list
is no longer necessary (for example, “555$”).
Table 6-3. Characters in AS-Path Pattern Matching
Symbol or
Operator
Meaning
< Denotes beginning of an AS SEQUENCE segment.
> Denotes end of an AS SEQUENCE segment.
{ Denotes beginning of an AS SET segment.
} Denotes end of an AS SET segment.
<
seq
>{
set
} denotes an AS path containing a sequence in the first segment and a
set in the second segment.
^ Denotes the following pattern occurs at the beginning of the AS path.
$ Denotes the preceding pattern occurs at the end of the AS path.
| Logical OR - match this or that.
_
X
_ Match exactly AS = “
X
”
_
X
Match AS pattern beginning with
X
(for example, ”_99” matches 99
991 9934)
X
_ Match AS pattern ending with
X
(for example, “99_” matches 99 199
23299)
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