Allied Telesis x900-48 series - Manual (Page 2)

Page 2 | AlliedWare™ OS How To Note: DHCP snooping on AT-9900-style switches
Introduction > What information will you find in this document?
This document explains each feature and provides the minimum configuration to enable
them. There are also two configuration examples that make advanced use of the features.
This document contains the following contents:
Introduction .............................................................................................................................................. 1
What information will you find in this document? ................................................................... 1
Which products and software version does this information apply to? .............................. 3
Related How To Notes ................................................................................................................... 3
DHCP snooping ....................................................................................................................................... 3
Minimum configuration ................................................................................................................... 4
The database ..................................................................................................................................... 5
Trusted and non-trusted ports ..................................................................................................... 7
Enabling DHCP snooping ............................................................................................................... 7
Static binding ..................................................................................................................................... 7
Completely removing the DHCP snooping database .............................................................. 8
DHCP Option 82 .................................................................................................................................... 9
Protocol details ................................................................................................................................. 9
Configuring Option 82 .................................................................................................................. 10
DHCP filtering ........................................................................................................................................ 11
Configuring filtering ....................................................................................................................... 12
Supporting multiple devices on a port ...................................................................................... 12
ARP security .................................................................................................................................... 13
Resource considerations .............................................................................................................. 14
Configuration examples ....................................................................................................................... 15
Configuring the switch for DHCP snooping, filtering, and Option 82, when it is
acting as a layer 2 switch ....................................................................................................... 15
Configuring the switch for DHCP snooping, filtering and Option 82, when it is
acting as a layer 3 BOOTP Relay Agent ............................................................................ 19
Troubleshooting ..................................................................................................................................... 23
No trusted ports configured ....................................................................................................... 23
The DHCP client continually sends requests instead of a discover ................................... 24
Maximum number of leases is exceeded .................................................................................. 24
Switch is dropping ARPs ............................................................................................................... 26
The DHCP ACK is dropped by the switch .............................................................................. 28
Cannot create a binding entry .................................................................................................... 34
Entries with client lease but no listeners .................................................................................. 36
Appendix 1: ISC DHCP server .......................................................................................................... 37