DHCP snooping database, local or database agent

[bvj197222]

I'm wondering if I need to have a database agent or just to keep the database local. Cisco says "To retain the bindings across switch reloads, you must use the DHCP snooping database agent. Without this agent, the bindings established by DHCP snooping are lost upon switch reload. Connectivity is lost as well.".

Exactly what happens if I have the database locally and I reboot the switch? If the only consequence is that the Clients have to reboot to get back online populating the snooping database, then why go thru the hazzle of setting up a server for the database? How long does it take to populate the snooping database after reboot? If you do have a database agent, what happens if the server that stores the database reboots?

[paul driver]

Hello

Exactly what happens if I have the database locally and I reboot the switch?

losing the D/B I guest on its own isn't that relevant as you have stated the users would have to at a  minimum release/renew there dhcp allocation to re populate the D/B  as these existing users wont have any reference in the binding D/B , I guess this would also apply when you have IPSG or DAI enabled.to.

The simplest solution would to save the d/b file centrally as suggested and not be in the position to lost it, but if you did and after a reload disabling the snooping and then re-enable it and letting it re-populate would be the only option.

If you do have a database agent, what happens if the server that stores the database reboots?

You can configure a write delay so to delay the writing to the D/B upto 1 day( 24 hrs) after a change has occurred.

res
Paul

[bvj197222]

Thanks for your answer. To make sure that I have understood this correctly;

Snooping database is stored locally and the switch reboot. The Clients will not get Connectivity until they reboot, initiating a New dhcp request. Is that the only consequence? Alternatively, I can turn off dhcp snooping to empty the table, and then turn dhcp snooping back on, then the Clients won't have to reboot.

Is this correct?

[paul driver]

Hello

They won’t have to reboot be they'll need to renew their addressing and if they are connected to the switch that reloads they will anyway.

As for hosts that are not directly connected to the switch that reloads and have registered with the snooping D/B that has been lost then they again will have to re-register as if you have something else like IPSG enabled also the switch wont allow connection as there won’t be any entry in snoop binding D/B for IPSG to check against.

I guess if you have very large site then getting everyone to renew their addressing or reload wouldn’t be applicable for just one switch going down, hence saving the snooping D/B off site would be a very good recommendation, but on the flip side I guess you would have snooping enable all switches that have dhcp clients attached.

res
Paul