Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 213)

• The PD notification fails when the DHCPv6 messages between a DHCPv6 server and a DHCPv6
client containing the PD option are not relayed via the DHCPv6 relay agent.
• If the delegated prefix is released or renewed by the client at the time when the DHCPv6 relay agent
is down or rebooting, then this release or renewal of the delegated prefix will not be detected by the
relay agent.
• If there is no sufficient disk space on a flash disk, then the system may not store all the delegated
prefixes in the IPv6 route table.
• The DHCPv6 PD flash operation will depend on the NTP clock synchronization. During system boot
up, if the NTP is configured, the flash operation (dhcp6_delegated_prefixes_data flash file read/write)
is delayed till the NTP is synchronized. The NTP synchronization is needed for the correct updation
of prefix age. If the NTP is not configured, then the DHCP prefix delegation will still read the flash, but
the prefix age may not be correct.
Upgrade and downgrade considerations
• When a router is upgraded to the version of software that supports this feature, the saved information
about delegated prefixes will be examined and if the delegated prefix lifetime is not expired, then the
prefix will be added to the IPv6 static route table.
• When a router is downgraded to the version of software that does not support this feature, the saved
information about delegated prefixes is retained and it cannot be used.
Configuring DHCPv6 Relay Agent Prefix Delegation Notification
To set the number of delegated prefixes that can be learned at the global system level, use the ipv6
dhcp-relay maximum-delegated-prefixes command.
By default, the DHCPv6 Relay Agent Prefix Delegation Notification is enabled when the DHCPv6 relay
agent feature is enabled on an interface. User can disable the DHCPv6 Relay Agent Prefix Delegation
Notification at the system or the interface level by setting ipv6 dhcp-relay maximum-delegated-
prefixes to 0 at the system or interface level as required.
NOTE
Make sure that there is enough free space in the flash memory to save information about delegated
prefixes in flash on both the Active and Standby management processor
device(config)# ipv6 dhcp-relay maximum-delegated-prefixes 500
Syntax: [no] ipv6 dhcp-relay maximum-delegated-prefixes value
The value parameter is used to limit the maximum number of prefixes that can be learnt at the global
level. The range is from 0 to 512. The default value is 500.
Use the no ipv6 dhcp-relay maximum-delegated-prefixes command to set the parameter to the
default value of the specified platform. See
Enabling DHCPv6 Relay Agent Prefix Delegation notification
on an interface on page 213 for more information.
Enabling DHCPv6 Relay Agent Prefix Delegation notification on an interface
To set the number of delegated prefixes that can be learned at the interface level, use the ipv6 dhcp-
relay maximum-delegated-prefixes command. This command limits the maximum number of prefixes
that can be learnt on the interface.
device(config-if-eth2/1)# ipv6 dhcp-relay maximum-delegated-prefixes 100
Upgrade and downgrade considerations
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