Configuring Persistent Bindings in the DHCP or DHCPv6 (ELS)
This task uses Junos OS with support for the Enhanced Layer 2 Software (ELS) configuration style.If your switch runs software that does not support ELS, see Configuring Persistent Bindings in the DHCP or DHCPv6 (non-ELS). For ELS details, see Using the Enhanced Layer 2 Software CLI.
By default, IP-MAC address bindings in the DHCP snooping database do not persist through device reboots. You can improve network performance by configuring the IP-MAC address bindings in the DHCP snooping database to persist through reboots so that the table does not need to be rebuilt after rebooting. Do this by configuring a storage location for the DHCP snooping database file, where you must specify how frequently the device writes the database entries into the DHCP snooping database file.
You can also configure persistent bindings for IPv6 addresses and MAC addresses on devices that support DHCPv6 snooping.
DHCPv6 is not supported on the MX Series routers.
The DHCP snooping database of IP-MAC bindings is created when you enable any of the port security features for a specific VLAN or bridge domain in either of the following hierarchy levels:
[edit vlans vlan-name forwarding-options dhcp-security][edit bridge-domains bridge-domain-name forwarding-options dhcp-security]
On devices that support DHCPv6, enabling any port security features will automatically enable DHCPv6 snooping. DHCP snooping and DHCPv6 snooping are not enabled by default.
By default, the IP-MAC bindings are lost when the
switch is rebooted, and the DHCP clients (the
network devices, or hosts) must reacquire
bindings. However, you can configure the bindings
to persist by setting the
dhcp-snooping-file statement to
store the database file either locally or
remotely. When you configure and enable 802.1x
dynamic VLAN, the DHCP snooping entries also get
deleted. Due to this, it is recommended to
configure for a DHCP server to store lease
information for clients and provide them with a
predictable IP address even after you reboot the
client (DHCP persistence).
To configure a local storage location for the DHCP snooping database file:
For DHCP snooping:
[edit system processes] user@device# set dhcp-service dhcp-snooping-file local-pathname write-interval seconds
For example:
[edit system processes] user@device# set dhcp-service dhcp-snooping-file /var/tmp/test.log write-interval 60
For DHCPv6 snooping:
[edit system processes] user@device# set dhcp-service dhcpv6-snooping-file local-pathname write-interval seconds
For example:
[edit system processes] user@device# set dhcp-service dhcpv6-snooping-file /var/tmp/test.log write-interval 60
To configure a remote storage location for IP-MAC bindings,
use tftp://ip-address or ftp://hostname/path as the remote URL, or the local pathname for the storage
location of the DHCP or DHCPv6 snooping database file:
For DHCP snooping:
[edit system processes] user@device# set dhcp-service dhcp-snooping-file remote_url write-interval seconds
For example:
[edit system processes] user@device# set dhcp-service dhcp-snooping-file tftp://@14.1.2.1 write-interval 60
For DHCPv6 snooping:
[edit system processes] user@device# set dhcp-service dhcpv6-snooping-file remote_url write-interval seconds
For example:
[edit system processes] user@device# set dhcp-service dhcpv6-snooping-file tftp://@14.1.2.1 write-interval 60
.