Allied Telesis AT-8600 Series, Rapier i Series manual The database, DHCP snooping database time-out

DHCP snooping

The database

The switch watches the DHCP packets that it is passing back-and-forth. It also maintains a database that lists the DHCP leases it knows are being held by devices downstream of its ports.

Each lease in the database holds the following information:

zthe MAC address of the client device

zthe IP address that was allocated to that client

ztime until expiry

zVLAN to which the client is attached

zthe port to which the client is attached

When inserting Option 82 information into the DHCP packets, the switch uses the information it has stored in the database for filtering and for filling in the fields.

DHCP snooping database time-out

The CPU will time-out database entries if the lease, also stored in the database, expires.

Database survival across reboots

The database is periodically saved as a .dsn file into non-volatile storage. Therefore the database will survive a reboot.

Verifying the status of snooped users

To verify the status of snooped users, use the command show dhcpsnooping database.

Manager > show dhcpsnooping database
DHCP Snooping Binding		Database
-------------------------------------------------------------------
Full Leases/Max Leases ... 1/52
Check Interval		60	seconds
Database Listeners		CLASSIFR
Current valid entries
MAC Address	IP	Address	Expires(s) VLAN	Port	ID	Source

-----------------------------------------------------------------------------

00-03-47-6b-a5-7a 10.11.67.50 56 48 16 3 Dynamic

-----------------------------------------------------------------------------

Entries with client lease but no listeners
MAC Address	IP Address	Expires(s) VLAN Port	ID	Source

-----------------------------------------------------------------------------

None...

-----------------------------------------------------------------------------

Entries with no client lease and no listeners

MAC Address IP Address Expires(s) VLAN Port ID Source

-----------------------------------------------------------------------------

None...

Page 4 AlliedWare™ OS How To Note: DHCP Snooping on Rapier-style switches