C
HAPTER
27
| General Security Measures
DHCPv6 Snooping
– 912 –
If a DHCPv6 packet from a client passes the filtering criteria above,
it will only be forwarded to trusted ports in the same VLAN.
DHCP Server Packet
n
If a DHCP server packet is received on an untrusted port, drop
this packet and add a log entry in the system.
n
If a DHCPv6 Reply packet is received from a server on a trusted
port, it will be processed in the following manner:
A. Check if IPv6 address in IA option is found in binding table:
n
If yes, continue to C.
n
If not, continue to B.
B. Check if IPv6 address in IA option is found in binding cache:
n
If yes, continue to C.
n
If not, check failed, and forward packet to trusted port.
C. Check status code in IA option:
n
If successful, and entry is in binding table, update lease
time and forward to original destination.
n
If successful, and entry is in binding cache, move entry
from binding cache to binding table, update lease time
and forward to original destination.
n
Otherwise, remove binding entry. and check failed.
n
If a DHCPv6 Relay packet is received, check the relay message
option in Relay-Forward or Relay-Reply packet, and process
client and server packets as described above.
u If DHCPv6 snooping is globally disabled, all dynamic bindings are
removed from the binding table.
u Additional considerations when the switch itself is a DHCPv6 client –
The port(s) through which the switch submits a client request to the
DHCPv6 server must be configured as trusted (using the ipv6 dhcp
snooping trust command). Note that the switch will not add a dynamic
entry for itself to the binding table when it receives an ACK message
from a DHCPv6 server. Also, when the switch sends out DHCPv6 client
packets for itself, no filtering takes place. However, when the switch
receives any messages from a DHCPv6 server, any packets received
from untrusted ports are dropped.
EXAMPLE
This example enables DHCPv6 snooping globally for the switch.
Console(config)#ipv6 dhcp snooping
Console(config)#
RELATED COMMANDS
ipv6 dhcp snooping vlan (913)
ipv6 dhcp snooping trust (914)
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