Configuring IP
December 2005 © Foundry Networks, Inc. 16 - 25
TACACS/TACACS+ Packets
To specify the lowest-numbered IP address configured on a virtual interface as the device’s source for all TACACS/
TACACS+ packets, enter commands such as the following:
FESX424 Router(config)# int ve 1
FESX424 Router(config-vif-1)# ip address 10.0.0.3/24
FESX424 Router(config-vif-1)# exit
FESX424 Router(config)# ip tacacs 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 TACACS/TACACS+ packets from the Layer 3 Switch.
Syntax: ip tacacs source-interface ethernet [<slotnum>/]<portnum> | loopback <num> | ve <num>
The <num> parameter is a loopback interface or virtual interface number. If you specify an Ethernet port, the
<portnum> is the port’s number (including the slot number, if you are configuring a Chassis device).
RADIUS Packets
To specify the lowest-numbered IP address configured on a virtual interface as the device’s source for all RADIUS
packets, enter commands such as the following:
FESX424 Router(config)# int ve 1
FESX424 Router(config-vif-1)# ip address 10.0.0.3/24
FESX424 Router(config-vif-1)# exit
FESX424 Router(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 [<slotnum>/]<portnum> | loopback <num> | ve <num>
The <num> parameter is a loopback interface or virtual interface number. If you specify an Ethernet port, the
<portnum> is the port’s number (including the slot number, if you are configuring a Chassis device).
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.
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