15-5
IP Routing Features
Overview of IP Routing
■ If the cache does not contain an entry, the software can create an entry in
the forwarding cache.
Each entry in the IP forwarding cache has an age timer. If the entry remains
unused for five minutes, the software removes the entry. The age timer is not
configurable.
Note You cannot add static entries to the IP forwarding cache.
IP Global Parameters for Routing Switches
The following table lists the IP global parameters and the page where you can
find more information about each parameter.
Table 15-1. IP Global Parameters for Routing Switches
Parameter Description Default See page
Address
Resolution
Protocol
(ARP)
A standard IP mechanism that routers use to learn the Media Access
Control (MAC) address of a device on the network. The router sends the
IP address of a device in the ARP request and receives the device’s MAC
address in an ARP reply.
Enabled 15-7
ARP age The amount of time the device keeps a MAC address learned through ARP
in the device’s ARP cache. The device resets the timer to zero each time
the ARP entry is refreshed and removes the entry if the timer reaches the
ARP age.
Five
minutes
not
configur-
able
Proxy ARP An IP mechanism a router can use to answer an ARP request on behalf
of a host. It replies with the router’s own MAC address instead of the
host’s.
Disabled 15-9
Time to Live
(TTL)
The maximum number of routers (hops) through which a packet can pass
before being discarded. Each router decreases a packet’s TTL by 1 before
forwarding the packet. If decreasing the TTL causes the TTL to be 0, the
router drops the packet instead of forwarding it.
64 hops 7-11
Directed
broadcast
forwarding
A directed broadcast is a packet containing all ones (or in some cases, all
zeros) in the host portion of the destination IP address. When a router
forwards such a broadcast, it sends a copy of the packet out each of its
enabled IP interfaces.
Note: You also can enable or disable this parameter on an individual
interface basis. See table 15-2 on page 15-6.
Disabled 15-10
!Software.book Page 5 Thursday, October 10, 2002 6:10 PM
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