Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

DHCP Snooping and Flash write limits

I undertsand that as default when a switch has DHCP Snooping enabled, then a database file is created and updated and this is held in Flash on the LAN Switch.

After an extended period of use is their a potential that the flash memory could exceed the maximum number of writes, as I understand that Flash memory supports a finite number of writes. I am concerned as I assume that the DHCP Snooping feature will lead to the database file being update many times throughout the lifetime of the LAN Switch, e.g. each time the lease time changes for each database entry. Our lease period is set to 15 days.

New Member

Re: DHCP Snooping and Flash write limits

Good question to bring up. I don't anticipate a problem though, but admit I may be making invalid assumptions. I know flash lasts usually between 1-2 million read/write cycles. Start with a 24 port switch and assume each device R/W's to one spot on the flash 10 times per day. That would equal 240 R/W cycles per day on that set of sectors. Or yearly, 87600 times. This would roughly equate to 11.4 years before flash gives out at the 1 million R/W spec.

How did I come up with 10 R/W per day? I looked at the DHCP snoop DB, and the only thing that I could see changing often was the lease timeout. Most DHCP scopes run at least 3 days and machine tries to renew after 1.5 days, which means probably another read/write cycle. This means about 1 time per day of R/W, and add in 10x for overhead. So I think I have the worst case scenario x 10 for R/W cylces. This is my assumption though!

In any case, I think the flash be able to take it! Any cisco insiders have the scoop on snoop?

CreatePlease to create content