Configuring Arp Parameters - Foundry Networks Switch and Router Installation And Configuration Manual

BigIron(config-vif-1)# exit
BigIron(config)# ip radius source-interface ve 1
The commands in this example configure virtual interface 1, assign IP address 10.0.0.3/24 to the interface, then
designate the interface as the source for all RADIUS packets from the Layer 3 Switch.
Syntax: ip radius source-interface ethernet <portnum> | pos <portnum> | loopback <num> | ve <num>
The <num> parameter is a loopback interface or virtual interface number. If you specify an Ethernet or POS port,
the <portnum> is the port's number (including the slot number, if you are configuring a chassis device).
USING THE WEB MANAGEMENT INTERFACE
You cannot configure a single source interface for Telnet, TACACS/TACACS+, or RADIUS using the Web
management interface.

Configuring ARP Parameters

Address Resolution Protocol (ARP) is a standard IP protocol that enables an IP Layer 3 Switch to obtain the MAC
address of another device's interface when the Layer 3 Switch knows the IP address of the interface. ARP is
enabled by default and cannot be disabled.
NOTE: Foundry Layer 2 Switches also support ARP. The description in "How ARP Works" also applies to ARP
on Foundry Layer 2 Switches. However, the configuration options described later in this section apply only to
Layer 3 Switches, not to Layer 2 Switches.
How ARP Works
A Layer 3 Switch needs to know a destination's MAC address when forwarding traffic, because the Layer 3 Switch
encapsulates the IP packet in a Layer 2 packet (MAC layer packet) and sends the Layer 2 packet to a MAC
interface on a device directly attached to the Layer 3 Switch. The device can be the packet's final destination or
the next-hop router toward the destination.
The Layer 3 Switch encapsulates IP packets in Layer 2 packets regardless of whether the ultimate destination is
locally attached or is multiple router hops away. Since the Layer 3 Switch's IP route table and IP forwarding cache
contain IP address information but not MAC address information, the Layer 3 Switch cannot forward IP packets
based solely on the information in the route table or forwarding cache. The Layer 3 Switch needs to know the
MAC address that corresponds with the IP address of either the packet's locally attached destination or the next-
hop router that leads to the destination.
For example, to forward a packet whose destination is multiple router hops away, the Layer 3 Switch must send
the packet to the next-hop router toward its destination, or to a default route or default network route if the IP route
table does not contain a route to the packet's destination. In each case, the Layer 3 Switch must encapsulate the
packet and address it to the MAC address of a locally attached device, the next-hop router toward the IP packet's
destination.
To obtain the MAC address required for forwarding a datagram, the Layer 3 Switch does the following:
• First, the Layer 3 Switch looks in the ARP cache (not the static ARP table) for an entry that lists the MAC
address for the IP address. The ARP cache maps IP addresses to MAC addresses. The cache also lists the
port attached to the device and, if the entry is dynamic, the age of the entry. A dynamic ARP entry enters the
cache when the Layer 3 Switch receives an ARP reply or receives an ARP request (which contains the
sender's IP address and MAC address). A static entry enters the ARP cache from the static ARP table (which
is a separate table) when the interface for the entry comes up.
To ensure the accuracy of the ARP cache, each dynamic entry has its own age timer. The timer is reset to
zero each time the Layer 3 Switch receives an ARP reply or ARP request containing the IP address and MAC
address of the entry. If a dynamic entry reaches its maximum allowable age, the entry times out and the
software removes the entry from the table. Static entries do not age out and can be removed only by you.
December 2000
Configuring IP
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