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AS Prepend and Local Preference for BGP

  • 30 April 2020
  • 3 replies
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Userlevel 1

Hi Community!

 

Is there any suggested documentation out there on configuring BGP AS Prepend and Local Preference for a Cumulus Switch?  The current Docs don’t show how to configure such a setup.  Our network is multi-homed to two providers and want to configure my BGP for a longer AS Prepend and low Local Preference on one of the providers so that it will be used for backup.

 

Thank you!

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Best answer by Eric Pulvino 30 April 2020, 23:08

You can use NCLU to configure AS-prepend.

cumulus@leaf01:~$ net add help | grep prepend
net (add|del) routing route-map <text> (deny|permit) <1-65535> set as-path prepend <1-4294967295> <1-4294967295> <1-4294967295> <1-4294967295> <1-4294967295>
net (add|del) routing route-map <text> (deny|permit) <1-65535> set as-path prepend last-as <1-10>

 

You can also use NCLU to configure local-pref.

 net (add|del) routing route-map <text> (deny|permit) <1-65535> set local-preference <0-4294967295>

 

Standard routing rules apply, increasing the as-prepend on the peering to one of your providers will make that path be less-preferred. A higher local preference is preferred and the default is 100.

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3 replies

Userlevel 5

You can use NCLU to configure AS-prepend.

cumulus@leaf01:~$ net add help | grep prepend
net (add|del) routing route-map <text> (deny|permit) <1-65535> set as-path prepend <1-4294967295> <1-4294967295> <1-4294967295> <1-4294967295> <1-4294967295>
net (add|del) routing route-map <text> (deny|permit) <1-65535> set as-path prepend last-as <1-10>

 

You can also use NCLU to configure local-pref.

 net (add|del) routing route-map <text> (deny|permit) <1-65535> set local-preference <0-4294967295>

 

Standard routing rules apply, increasing the as-prepend on the peering to one of your providers will make that path be less-preferred. A higher local preference is preferred and the default is 100.

Userlevel 1

Wonderful!  Thanks for that “help” command Eric :smile:   Will give that a shot and configure.

 

Thanks again!

Userlevel 4

Thanks for letting us know about this @Melvin! We’re tracking this in our JIRA and will get these two commands documented soon.

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