General Configuration Using Local Management
CSX400 and CSX400-DC User’s Guide 159
3. Use the arrow keys to highlight the SAVE command field at the bottom of the screen and then
press ENTER. The message “SAVED OK” displays.
The entry for the UDP Port option reflects the UDP port number that is currently selected. The
entry for UDP Type names the UDP service to which that port number corresponds.
Enabling Proxy ARP on a Port
By default, Proxy Address Resolution Protocol (ARP) is disabled on all ports, and IP Routing
Services respond only to ARP requests addressed to its own IP address.
For one IP host to communicate with another IP host, knowledge of the target host’s MAC address
must be known. To learn this MAC address, the IP host sends an ARP request packet as a LAN
broadcast with the destination IP address of the target IP host. All hosts receive this broadcast and
the one host that matches the target IP address responds with its MAC-layer address. However,
because each subnet constitutes a separate broadcast domain and LAN broadcasts are not
forwarded across routers, ARP does not work beyond a host’s local network or subnetwork. One of
the primary purposes of a router is to confine LAN broadcast traffic to each local network or
subnetwork.
A proxy ARP response is generated when the following occurs:
•Proxy ARP is enabled on a router port.
•An ARP request is received as a LAN broadcast (looking for the MAC-layer address of an IP
host on another network segment).
•An entry exists in the IP Forwarding Table for the destination host’s network.
Enabling Proxy ARP on a router port allows IP hosts to dynamically obtain the MAC-layer address
of other IP hosts attached to different networks or subnetworks by using broadcast ARP request
packets. With Proxy ARP enabled, IP hosts are not required to maintain knowledge of specific
subnetworks.
To enable Proxy ARP on a router port, complete the following steps:
1. Use the arrow keys to highlight the Proxy ARP option.
2. Use the ENTER key to toggle the entry to ENABLED.
NOTE You can type in the UDP port number, or you can use the +REDIRECTOR- option at
the bottom of the screen to scroll through a list of commonly used UDP port numbers.
To use the +REDIRECTOR- option, use the arrow keys to highlight the + (to go
forward), or the - (to go backward), and then press the ENTER key to scroll in the
direction that you selected.