Routing

" clear ospf database purge  "

 

in which case I need to address this command?

Hi,

 

good question.

This command forces the router to send out all LSAs in its database (learned and self-originated) after setting them to MAXAGE. Here is what happens when this command is issued:

 

1) The router marks all LSAs as MAXAGE and sends them out.

2) The actual originators of those LSAs now receive these LSAs and re-originate them.

3) Effectively you're refreshing the OSPF database of the whole area.

 

Here is a small piece of documentation from Juniper's website:

 

(Optional) Discard all entries in the link-state advertisement database. All link-state advertisements are set to MAXAGE and are flooded. The database is repopulated when the originators of the link-state advertisements receive the MAXAGE link-state advertisements and reissue them.

 

link: http://www.juniper.net/techpubs/en_US/junos10.1/information-products/topic-collections/swcmdref-protocols/topic-19017.html

 

cheers,

ankit

 

hello,

thanks

 

btw:normally ospf will refresh its database,why we need to clear it?

 

automatically refresh has some timer?

Hi

    1、OSPF sends out its self-originated LSAs when the LSA age reaches the link-state refresh time, which is 1800 seconds. 

     2、Unless OSPF process daemon is out of order, I have no idea why we have to clear the database. Becoz it should be updated automatically.

Hi

    With the master Routing Engine , delete entries in the Open Shortest Path First (OSPF) link-state advertisement (LSA) database. With the backup Routing Engine, delete the OSPF LSA database and sync the new database with the master Routing Engine. You can also use purge with any of the options to discard rather than delete the specified LSA entries.

    Caution: This command is useful only for testing. Use it with care because it causes significant network disruption.

 

   You can refer to below hyperlink for detail. 

 

http://www.juniper.net/techpubs/software/junos/junos93/swcmdref-protocols/clear-ospf-ospf3-database.html

 

   BTW

           The OSPF standard requires that every link-state advertisement (LSA) be refreshed every 30 minutes（1800 seconds）. The Juniper implementation refreshes LSAs every 50 mintues（3000 seconds）. 

You're right. We'll need to do this only if we suspect something wrong with ospf and want to clear the database of all routers within an area at the same time.