Chapter 17
| General IP Routing
Address Resolution Protocol
– 642 –
Address Resolution Protocol
If IP routing is enabled (page
), the router uses its routing tables to make routing
decisions, and uses Address Resolution Protocol (ARP) to forward traffic from one
hop to the next. ARP is used to map an IP address to a physical layer (i.e., MAC)
address. When an IP frame is received by this router (or any standards-based
router), it first looks up the MAC address corresponding to the destination IP
address in the ARP cache. If the address is found, the router writes the MAC address
into the appropriate field in the frame header, and forwards the frame on to the
next hop. IP traffic passes along the path to its final destination in this way, with
each routing device mapping the destination IP address to the MAC address of the
next hop toward the recipient, until the packet is delivered to the final destination.
If there is no entry for an IP address in the ARP cache, the router will broadcast an
ARP request packet to all devices on the network. The ARP request contains the
following fields similar to that shown in this example:
When devices receive this request, they discard it if their address does not match
the destination IP address in the message. However, if it does match, they write
their own hardware address into the destination MAC address field and send the
message back to the source hardware address. When the source device receives a
reply, it writes the destination IP address and corresponding MAC address into its
cache, and forwards the IP traffic on to the next hop. As long as this entry has not
timed out, the router will be able forward traffic directly to the next hop for this
destination without having to broadcast another ARP request.
Also, if the switch receives a request for its own IP address, it will send back a
response, and also cache the MAC of the source device's IP address.
Basic ARP
Configuration
Use the IP > ARP (Configure General) page to specify the timeout for ARP cache
entries, or to enable Proxy ARP for specific VLAN interfaces.
Command Usage
Proxy ARP
When a node in the attached subnetwork does not have routing or a default
gateway configured, Proxy ARP can be used to forward ARP requests to a remote
subnetwork. When the router receives an ARP request for a remote network and
Proxy ARP is enabled, it determines if it has the best route to the remote network,
and then answers the ARP request by sending its own MAC address to the
Table 41: Address Resolution Protocol
destination IP address
10.1.0.19
destination MAC address
?
source IP address
10.1.0.253
source MAC address
00-00-ab-cd-00-00
Содержание GTL-2881
Страница 30: ...Figures 30 Figure 450 Showing RIP Peer Information 669 Figure 451 Resetting RIP Statistics 670 ...
Страница 34: ...Section I Getting Started 34 ...
Страница 48: ...Section II Web Configuration 48 Unicast Routing on page 651 ...
Страница 151: ...Chapter 4 Interface Configuration VLAN Trunking 151 Figure 69 Configuring VLAN Trunking ...
Страница 152: ...Chapter 4 Interface Configuration VLAN Trunking 152 ...
Страница 229: ...Chapter 8 Congestion Control Automatic Traffic Control 229 Figure 135 Configuring ATC Interface Attributes ...
Страница 230: ...Chapter 8 Congestion Control Automatic Traffic Control 230 ...
Страница 596: ...Chapter 14 Multicast Filtering Multicast VLAN Registration for IPv6 596 ...
Страница 620: ...Chapter 15 IP Configuration Setting the Switch s IP Address IP Version 6 620 ...
Страница 670: ...Chapter 18 Unicast Routing Configuring the Routing Information Protocol 670 Figure 451 Resetting RIP Statistics ...
Страница 672: ...Section III Appendices 672 ...
Страница 678: ...Appendix A Software Specifications Management Information Bases 678 ...
Страница 688: ...Appendix C License Statement GPL Code Statement Notification of Compliance 688 ...
Страница 696: ...Glossary 696 ...
Страница 706: ...GTL 2881 GTL 2882 E112016 ST R01 ...