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    40-BGP Regular Expression

    Uploaded by

    prakashrjsekar
    Regular expressions can be used in BGP routing to match routes based on attributes like the AS path. Special characters are used to create patterns to search for and extract useful information from BGP tables. Common uses include finding routes originated or passed through a specific AS.

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    © All Rights Reserved
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    40-BGP Regular Expression

    Uploaded by

    prakashrjsekar
    91 views5 pages
    Regular expressions can be used in BGP routing to match routes based on attributes like the AS path. Special characters are used to create patterns to search for and extract useful information from BGP tables. Common uses include finding routes originated or passed through a specific AS.

    Original Title

    40-BGP+Regular+Expression

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    Regular expressions can be used in BGP routing to match routes based on attributes like the AS path. Special characters are used to create patterns to search for and extract useful information from BGP tables. Common uses include finding routes originated or passed through a specific AS.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    91 views5 pages

    40-BGP Regular Expression

    Uploaded by

    prakashrjsekar
    Regular expressions can be used in BGP routing to match routes based on attributes like the AS path. Special characters are used to create patterns to search for and extract useful information from BGP tables. Common uses include finding routes originated or passed through a specific AS.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 5

    BGP Regular Expression:

    A regular expression is a pattern used to match against an input string. It is a widely used tool.
    In BGP routing policy deployment, regular expressions can also be flexibly used to obtain
    routes. A BGP route contains the AS_Path attribute. Regular expressions can be used to obtain
    routes with a specific AS number or AS_Path attribute. Regular expressions are strings of special
    characters that can be used to search and find character patterns. Within the scope of BGP in
    Cisco IOS regular expressions can be used in show commands and AS-Path access- lists to match
    BGP prefixes based on the information contained in their AS-Path. A regular expression is a
    formula for matching strings that follow a certain pattern. It evaluates text data & returns an
    answer of true or false. BGP Regular Expressions are special characters used to get useful
    information from BGP tables. Use the show ip bgp regexp command to display routes matching
    the specified regular expression.

    Character/Symbol Special Meaning


    Asterisk * Matches 0 or more sequences of the pattern.
    Brackets [] Designates a range of single-character patterns.
    Caret ^ Matches the beginning of the input string.
    Dollar Sign $ Matches the end of the input string.
    Hyphen - Separates the end points of a range.
    Parentheses () Logical grouping.
    Period . Matches any single character, including white space.
    Plus Sign + Matches 1 or more sequences of the pattern.
    Question Mark ? Matches 0 or 1 occurrences of the pattern.
    Underscore _ Matches a space.
    Pipe | Provides or functionality to the query.
    Caret in brackets [^] Excludes the characters listed in brackets.

    Expression Meaning
    .* Anything
    ^$ Locally originated Routes
    ^ 7474 _ Learned from AS 7474
    _ 7474$ Originated in AS 7474
    _ 7474_ Any instance of AS 7474
    ^[0-9]+$ Directly Connected AS

    https://bgp4.as/looking-glasses

    1 | P a g e Created by Ahmad Ali E-Mail: ahmadalimsc@gmail.com , Mobile: 056 430 3717


    Create a regular expression that shows all networks that originate in AS 7474.
    Show ip bgp regexp _7474$

    To find all subnets reachable via AS 7474 (AS path begins with 7474).
    show ip bgp regexp ^7474_

    2 | P a g e Created by Ahmad Ali E-Mail: ahmadalimsc@gmail.com , Mobile: 056 430 3717


    Create a regular expression that shows AS 7474 at the beginning, and everything behind it.
    Show ip bgp regexp ^7474_

    Shows everything where AS 6762 is in the middle of the AS-PATH.


    show ip bgp regexp _6762_

    3 | P a g e Created by Ahmad Ali E-Mail: ahmadalimsc@gmail.com , Mobile: 056 430 3717


    Create a regular expression that only shows the locally originated networks.
    Show ip bgp regexp ^$

    To match all the networks in BGP table.


    Show ip bgp regexp .*

    Show all networks that are originated by your directly connected AS neighbors.
    Show ip bgp regexp ^[0-9]+$

    4 | P a g e Created by Ahmad Ali E-Mail: ahmadalimsc@gmail.com , Mobile: 056 430 3717


    Create a regular expression that only shows AS 7474.
    Show ip bgp regexp ^7474$

    5 | P a g e Created by Ahmad Ali E-Mail: ahmadalimsc@gmail.com , Mobile: 056 430 3717

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