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Nest: Implement BGP path mask loop operator

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Implement regex-like '+' operator in BGP path masks to match previous
path mask item multiple times. This is useful as ASNs may appear
multiple times in paths due to path prepending for traffic engineering
purposes.
This commit is contained in:
Ondrej Zajicek (work)
2020-05-18 16:25:08 +02:00
parent 5fc8407177
commit ec430a7fee
7 changed files with 86 additions and 29 deletions
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doc/bird.sgml
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@@ -1471,11 +1471,16 @@ in the foot).
<cf/*/ matches any (even empty) sequence of arbitrary AS numbers and
<cf/?/ matches one arbitrary AS number. For example, if <cf>bgp_path</cf>
is 4 3 2 1, then: <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true,
but <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false. BGP mask
expressions can also contain integer expressions enclosed in parenthesis
and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>. You can
also use ranges (e.g. <tt>[= * 3..5 2 100..200 * =]</tt>) and sets
(e.g. <tt>[= 1 2 [3, 5, 7] * =]</tt>).
but <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false. There is also
<cf/+/ operator which matches one or multiple instances of previous
expression, e.g. <tt>[= 1 2+ 3 =]</tt> matches both path 1 2 3 and path
1 2 2 2 3, but not 1 3 nor 1 2 4 3. Note that while <cf/*/ and <cf/?/
are wildcard-style operators, <cf/+/ is regex-style operator.
BGP mask expressions can also contain integer expressions enclosed in
parenthesis and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
You can also use ranges (e.g. <tt>[= * 3..5 2 100..200 * =]</tt>)
and sets (e.g. <tt>[= 1 2 [3, 5, 7] * =]</tt>).
<tag><label id="type-clist">clist</tag>
Clist is similar to a set, except that unlike other sets, it can be