Users Guide

Layer 3 Routing Commands 1855
Command Mode
Global Configuration mode
User Guidelines
This command enables the uRPF feature in hardware. When the uRPF check
is enabled, the route table is checked for source and destination IP match in
parallel. For this reason, the route table capacity is reduced once this feature
is enabled. A message to this effect is displayed to the user. This command
enables the mode for both v4 and v6.
This command also causes the IP routing to be disabled and re-enabled if it
was enabled prior to issuing the command.
uRPF supports two modes of source IP check:
• Strict mode – The path to the source IP address must be through the
SAME interface as that on which the packet arrived.
• Loose mode – The path to the source IP address can be through any
interface on the device.
The allowed default option, when used in conjunction with loose mode,
considers the default route (if present) in the routing table if the specified
prefix is not found.
The allowed default option, when used in conjunction with strict mode,
passes the uRPF check only if the packet arrives on the interface(s) where the
default route is learned.
uRPF checks do not work for multicast packets or for link-local IPv6
addresses.
uRPF checks are not performed on a BOOTP/DHCP packet (SIP is 0.0.0.0
and DIP is FF.FF.FF.FF).
uRPF logs missed uRPF checks in the system log.
Unicast RPF loose mode may be used on an uplink interface which has a
default route associated with it. For example, a single–homed environment
with symmetric routing meets this requirement.