Description

The following information describes the configuration steps to preserve the DHCP Snooping Database during an unplanned event such as power loss.

Symptoms

Prior to JUNOS 9.4 release, DHCP snooping binding database is lost when there is an unplanned events such as power loss. Certain end-hosts will not release the IP address information when the link goes down – thus an inconsistency can occur. DHCP Snooping database inconsistency will not only affect the operation of DHCP itself, but also any other features that are dependent on the DHCP Snooping Binding Database such as Dynamic ARP Inspection (DAI) and IP Source Guard (IPSG).

Solution

EX-series switches allow users (JUNOS 9.4 and above) to preserve the DHCP snooping binding database in a file. DHCP snooping binding database can also be saved on a remote server by specifying the URL. User can also define the time interval that the file will be written or to load/save the DHCP snooping binding database manually. Once DHCP snooping persistent database is configured, the saved database file will be loaded automatically when the switch powers up after unexpected event.

  • To configure DHCP Snooping persistent:

edit ethernet-switching-options secure-access-port]
dhcp-snoop-file {
   location <file/URL> ;
   write-interval <seconds> ;
   timeout <seconds> ;
}
  • Location can be a local file or URL in the following format (FTP or TFTP):

ftp:// <IP address or hostname> /PATH
  • CLI Command mode is also supported for “manual” load and save:

load dhcp-snooping <filename>
save dhcp-snooping <filename>
  • To monitor the DHCP Snooping Persistence statistics:

user@switch> show dhcp snooping statistics
DHCP Snoop Persistence statistics
Successful Remote Transfers: 0           Failed Remote Transfers: 0     
Successful Record Reads    : 12           Failed Remote Reads    : 0     
Successful Record Writes   : 12           Failed Record Writes   : 0