HP 6120XG HP ProCurve Series 6120 Blade Switches Multicast and Routing Guide - Page 62

Configuring Forwarding Parameters, Changing the TTL Threshold

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IP Routing Features Configuring IP Parameters for Routing Switches ARP requests contain the IP address and MAC address of the sender, so all devices that receive the request learn the MAC address and IP address of the sender and can update their own ARP caches accordingly. Note: The ARP request broadcast is a MAC broadcast, which means the broadcast goes only to devices that are directly attached to the routing switch. A MAC broadcast is not routed to other networks. Note If the routing switch receives an ARP request packet that it is unable to deliver to the final destination because of the ARP time-out and no ARP response is received (the routing switch knows of no route to the destination address), the routing switch sends an ICMP Host Unreachable message to the source. Note Configuring Forwarding Parameters The following configurable parameters control the forwarding behavior of ProCurve routing switches: ■ Time-To-Live (TTL) threshold ■ Forwarding of directed broadcasts All these parameters are global and thus affect all IP interfaces configured on the routing switch. To configure these parameters, use the procedures in the following sections. Changing the TTL Threshold The configuration of this parameter is covered in the chapter titled, "Config­ uring IP Addressing" in the Management and Configuration Guide for your routing switch. Enabling Forwarding of Directed Broadcasts A directed broadcast is an IP broadcast to all devices within a single directlyattached 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. 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. 3-16

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IP Routing Features
Configuring IP Parameters for Routing Switches
ARP requests contain the IP address and MAC address of the sender, so
all devices that receive the request learn the MAC address and IP address
of the sender and can update their own ARP caches accordingly.
Note:
The ARP request broadcast is a MAC broadcast, which means the
broadcast goes only to devices that are directly attached to the routing
switch. A MAC broadcast is not routed to other networks.
Note
If the routing switch receives an ARP request packet that it is unable to deliver
to the final destination because of the ARP time-out and no ARP response is
received (the routing switch knows of no route to the destination address),
the routing switch sends an ICMP Host Unreachable message to the source.
Configuring Forwarding Parameters
The following configurable parameters control the forwarding behavior of
ProCurve routing switches:
■
Time-To-Live (TTL) threshold
■
Forwarding of directed broadcasts
All these parameters are global and thus affect all IP interfaces configured on
the routing switch.
To configure these parameters, use the procedures in the following sections.
Changing the TTL Threshold
The configuration of this parameter is covered in the chapter titled, “Config-
uring IP Addressing” in the
Management and Configuration Guide
for your
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.
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