Multicast and Routing Guide K/KA/KB.15.15

When proxy ARP is enabled, all valid ARP requests receive a response if the following conditions
are met:
• There is a route to the target IP address in the ARP request (this can be a route or default route),
and the VLAN (interface) the ARP request is received on does NOT match the interface for
the next hop in the matched route to get to the target IP address.
AND
• There is a route back to the source IP address in the ARP request and the interface the ARP
request came in on DOES match the interface for the nex thop in the matched route to get to
the source IP address.
Configuring forwarding parameters
The following configurable parameters control the forwarding behavior of HP routing switches:
• Time-To-Live (TTL) threshold
For more information, see the Management and Configuration Guide for your switch.
• Forwarding of directed broadcasts
These parameters are global and thus affect all IP interfaces configured on the routing switch.
Enabling forwarding of directed broadcasts
A directed broadcast is an IP broadcast to all devices within a single directly-attached network or
subnet. A net-directed broadcast goes to all devices on a given network. A subnet-directed broadcast
goes to all devices within a given subnet.
NOTE: A less common type, the all-subnets broadcast, goes to all directly-attached subnets.
Forwarding for this broadcast type also is supported, but most networks use IP multicasting instead
of all-subnet broadcasting.
Forwarding for all types of IP directed broadcasts is disabled by default. You can enable forwarding
for all types if needed. You cannot enable forwarding for specific broadcast types.
Configuring ICMP
You can configure the following ICMP limits:
Burst-normal The maximum number of ICMP replies to send per second.
Reply limit You can enable or disable ICMP reply rate limiting.
Disabling ICMP messages
HP devices are enabled to reply to ICMP echo messages and send ICMP Destination Unreachable
messages by default.
You can selectively disable the following types of Internet Control Message Protocol (ICMP)
messages:
Echo messages (ping messages) The routing switch replies to IP pings from other IP devices.
Destination unreachable messages If the routing switch receives an IP packet that it cannot
deliver to its destination, the routing switch discards the
packet and sends a message back to the device that sent
the packet to the routing switch. The message informs the
device that the destination cannot be reached by the routing
switch.
Address mask replies You can enable or disable ICMP address mask replies.
120 Routing Basics