Section 4: Configuring L3 Features; Configuring Arp - D-Link DWS-4026 User Manual

Software User Manual
12/10/09
S e c t i on 4 : C on f i gu r i ng L3 F e a t ur e s
D-Link Unified Access System supports IP routing. Use the links in the LAN > L3 Features navigation tree folder to manage
routing on the system. This section contains the following information:
•

"Configuring ARP"

• "Configuring Global and Interface IP Settings"
• "Managing the BOOTP/DHCP Relay Agent"
• "Configuring RIP"
• "Router Discovery"
• "Router"
• "VLAN Routing"
• "Virtual Router Redundancy Protocol (VRRP)"
• "Loopback Interfaces"
When a packet enters the switch, the destination MAC address is checked to see if it matches any of the configured routing
interfaces. If it does, then the silicon searches the host table for a matching destination IP address. If an entry is found, then
the packet is routed to the host. If there is not a matching entry, then the switch performs a longest prefix match on the
destination IP address. If an entry is found, then the packet is routed to the next hop. If there is no match, then the packet is
routed to the next hop specified in the default route. If there is no default route configured, then the packet is passed to the
CPU to be handled appropriately.
The routing table can have entries added either statically by the administrator or dynamically via a routing protocol. The host
table can have entries added either statically by the administrator or dynamically via ARP.
C ARP
ONFIGURING
The ARP protocol associates a layer 2 MAC address with a layer 3 IPv4 address. D-Link software features both dynamic
and manual ARP configuration. With manual ARP configuration, you can statically add entries into the ARP table.
ARP is a necessary part of the internet protocol (IP) and is used to translate an IP address to a media (MAC) address,
defined by a local area network (LAN) such as Ethernet. A station needing to send an IP packet must learn the MAC address
of the IP destination, or of the next hop router, if the destination is not on the same subnet. This is achieved by broadcasting
an ARP request packet, to which the intended recipient responds by unicasting an ARP reply containing its MAC address.
Once learned, the MAC address is used in the destination address field of the layer 2 header prepended to the IP packet.
The ARP cache is a table maintained locally in each station on a network. ARP cache entries are learned by examining the
source information in the ARP packet payload fields, regardless of whether it is an ARP request or response. Thus, when
an ARP request is broadcast to all stations on a LAN segment or virtual LAN (VLAN), every recipient has the opportunity to
store the sender's IP and MAC address in their respective ARP cache. The ARP response, being unicast, is normally seen
only by the requestor, who stores the sender information in its ARP cache. Newer information always replaces existing
content in the ARP cache.
The number of supported ARP entries is 2048 for the D-Link Unified Switch.
Devices can be moved in a network, which means the IP address that was at one time associated with a certain MAC
address is now found using a different MAC, or may have disappeared from the network altogether (i.e., it has been
Document 34CSFP6XXUWS-SWUM100-D7
D-Link Unified Access System
Configuring L3 Features Page 279