The ability to perform a filter match on confederations in the AS path and/or communities is supported. This filter allows customers to configure match criteria for specific confederation sets and sequences within the AS path so that they can be filtered out before cluttering the service provider’s routing information base (RIB). When matching communities, the filter allows customers to configure match criteria within the community value.
SR OS uses regular expression strings to specify match criteria for:
an AS path string; for example, ‟100 200 300”
a community string; for example, ‟100:200” where 100 is the AS number, and 200 is the community-value
any AS path beginning with a confederation SET or SEQ containing 65001 and 65002 only: for example, ‟< 65001 65002 >.*”
any AS path containing a confederation SET or SEQ, regardless of the contents: for example, ‟.* <.*> .*”
A regular expression is expressed in the form of terms and operators.
A term for an AS path regular expression must meet the following criteria.
Regular expressions should always be enclosed in quotes.
An elementary term; for example, an AS number ‟200”
A range term composed of two elementary terms separated by the ‟-” character, such as ‟200-300”.
The ‟.” dot wild-card character which matches any elementary term.
A regular expression enclosed in parenthesis ‟( )”.
A regular expression enclosed in square brackets used to specify a set of choices of elementary or range terms; for example, [100-300 400] matches any AS number between 100 and 300 or the AS number 400.
A term for a community string regular expression is a string that is evaluated character by character and is composed of:
an elementary term, which for a community string, is any single digit, such as ‟4”
A range term composed of two elementary terms separated by the ‛-’ character like ‟2-3”
a colon ‟:” to delimit the AS number from the community value
the ‟.” dot wild-card character which matches any elementary term or ':'
a regular expression enclosed in parenthesis ‟( )”
a regular expression enclosed in square brackets used to specify a set of choices of elementary or range terms; for example, [51-37] matches digit 5 or any single digit between 1 and 3 or the digit 7
extended communities of type route-target and route-origin may embed two regular expressions separated by ONE ampersand ‟'&”) character; the first expression is applied to the as-value of the community string and the second to the local administrative value
large communities may embed three regular expressions separated by two ampersand (‟&”) characters; the first expression is applied to the Global Administrator part of the large community, the second expression is applied to the Local Data part 1 element of the large community, and the third expression is applied to the Local Data part 2 element of the large community
A raw hex format can be keyed to represent all extended communities. For example, "ext:0102:dc0000020032" is the same as ‟target:65530:20”. Hex values ‟ext:” and ‟&” can also be used to filter extended communities. The first expression is applied to the type/subtype of the extended community and the second expression to the value. In this case, hex values can also be used in the operands; for example, the value {3,f} matches a minimum 3 and a maximum 15 repetitions of the term.
The regular expression OPERATORS are listed in Table: Regular expression operators .
| Operator | Description |
|---|---|
| |
Matches the term on alternate sides of the pipe. |
* |
Matches multiple occurrences of the term. |
? |
Matches 0 or 1 occurrence of the term. |
+ |
Matches 1 or more occurrence of the term. |
( ) |
Used to parenthesize so a regular expression is considered as one term. |
[ ] |
Used to demarcate a set of elementary or range terms. |
- |
Used between the start and end of a range. |
{m,n} |
Matches least m and at most n repetitions of the term. |
{m} |
Matches exactly m repetitions of the term. |
{m,} |
Matches m or more repetitions of the term. |
^ |
Matches the beginning of the string - only allowed for communities. |
$ |
Matches the end of the string - only allowed for communities. |
\ |
An escape character to indicate that the following character is a match criteria and not a grouping delimiter. |
<> |
Matches any AS path numbers containing a confederation SET or SEQ. |
& |
Matches ‟:” between terms of a community string (applicable to extended communities origin, target, bandwidth, ext only). |
Examples of ‟target:”, ‟origin:” and ‟ext:” community strings are listed in Table: Community strings examples .
| Example expression | Example matches |
|---|---|
"ext:..&f(.*)[af]$" |
Matches the community "ext:0002:fffa0000001a". |
'target:1&22 |
Matches community target:100:221. |
target:^1&^22 |
Matches community target:100:221. |
target:(.*)0$&(.*)1$ |
Matches community target:100:221. |
origin:^1&(.*)1$ |
Matches community origin:100:221. |
Examples of AS path and community string regular expressions are listed in Table: AS path and community regular expression examples .
| AS path to match criteria | Regular expression | Example matches |
|---|---|---|
Null AS path |
null1 |
Null AS path |
AS path is 11 |
11 |
11 |
AS path is 11 22 33 |
11 22 33 |
11 22 33 |
Zero or more occurrences of AS number 11 |
11* |
Null AS path 11 11 11 11 11 11 11 … 11 |
Path of any length that begins with AS numbers 11, 22, 33 |
11 22 33 .* |
11 22 33 11 22 33 400 500 600 |
Path of any length that ends with AS numbers 44, 55, 66 |
.* 44 55 66 |
44 55 66 100 44 55 66 100 200 44 55 66 100 200 300 44 55 66 100 200 300 … 44 55 66 |
One occurrence of the AS numbers 100 and 200, followed by one or more occurrences of the number 33 |
100 200 33+ |
100 200 33 100 200 33 33 100 200 33 33 33 100 200 33 33 33 … 33 |
One or more occurrences of AS number 11, followed by one or more occurrences of AS number 22, followed by one or more occurrences of AS number 33 |
11+ 22+ 33+ |
11 22 33 11 11 22 33 11 11 22 22 33 11 11 22 22 33 33 11 … 11 22 … 22 33 …33 |
Path whose second AS number must be 11 or 22 |
(. 11) | (. 22) .* or . (11 | 22) .* |
100 11 200 22 300 400 … |
Path of length one or two whose second AS number may be 11 or 22 |
. (11 | 22)? |
100 200 11 300 22 |
Path whose first AS number is 100 and second AS number is either 11 or 22 |
100 (11 | 22) .* |
100 11 100 22 200 300 |
Either AS path 11, 22, or 33 |
[11 22 33] |
11 22 33 |
Range of AS numbers to match a single AS number |
10-14 |
10 or 11 or 12 or 13 or 14 |
[10-12]* |
Null AS path 10 or 11 or 12 10 10 or 10 11 or 10 12 11 10 or 11 11 or 11 12 12 10 or 12 11 or 12 12 … |
|
Zero or one occurrence of AS number 11 |
11? or 11{0,1} |
Null AS path 11 |
One through four occurrences of AS number 11 |
11{1,4} |
11 11 11 11 11 11 11 11 11 11 |
One through four occurrences of AS number 11 followed by one occurrence of AS number 22 |
11{1,4} 22 |
11 22 11 11 22 11 11 11 22 11 11 11 11 22 |
Path of any length, except nonexistent, whose second AS number can be anything, including nonexistent |
. .* or . .{0,} |
100 100 200 11 22 33 44 55 |
AS number is 100. Community value is 200. |
^100:200$ |
100:200 |
AS number is 11 or 22. Community value is any number. |
^((11)|(22)):(.*)$ |
11:100 22:100 11:200 … |
AS number is 11. Community value is any number that starts with 1. |
^11:(1.*)$ |
11:1 11:100 11:1100 … |
AS number is any number. Community value is any number that ends with 1, 2, or 3. |
^(.*):(.*[1-3])$ |
11:1 100:2002 333:55553 … |
AS number is 11 or 22. Community value is any number that starts with 3 and ends with 4, 5 or 9. |
^((11)|(22)):(3.*[459])$ |
11:34 22:3335 11:3777779 … |
AS number is 11 or 22. Community value ends in 33 or 44. |
[^((11|22)):(.*((33)|(44)))$ |
11:33 22:99944 22:555533 … |
Range of Community values |
100&^([1-9][0-9]|[1-9][0-9][0-9]|1[0-9][0-9][0-9]|2000)$" |
100:10 100:11 100: … 100:2000 |