C
HAPTER
18
| General IP Routing
Address Resolution Protocol
– 496 –
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.
B
ASIC
ARP
C
ONFIGURATION
Use the IP > ARP (Configure General) page to specify the timeout for ARP
cache entries, or to enable Proxy ARP for specific VLAN interfaces.
CLI R
EFERENCES
u
u
C
OMMAND
U
SAGE
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 requesting node. That node then sends
traffic to the router, which in turn uses its own routing table to forward the
traffic to the remote destination.
Figure 289: Proxy ARP
Table 30: 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
no routing,
no default
gateway
Remote
ARP Server
Proxy ARP
ARP
request
Summary of Contents for DG-GS4826S
Page 2: ...DG GS4826S DG GS4850S E012011 R01 F1 2 2 0 ...
Page 4: ......
Page 6: ...ABOUT THIS GUIDE 6 ...
Page 60: ...SECTION I Getting Started 60 ...
Page 72: ...CHAPTER 1 Introduction System Defaults 72 ...
Page 90: ...CHAPTER 2 Initial Switch Configuration Managing System Files 90 ...
Page 92: ...SECTION II Web Configuration 92 u Unicast Routing on page 539 u Multicast Routing on page 595 ...
Page 138: ...CHAPTER 4 Basic Management Tasks Resetting the System 138 ...
Page 204: ...CHAPTER 6 VLAN Configuration Configuring MAC based VLANs 204 ...
Page 212: ...CHAPTER 7 Address Table Settings Clearing the Dynamic Address Table 212 ...
Page 238: ...CHAPTER 9 Rate Limit Configuration 238 Figure 106 Configuring Rate Limits ...
Page 268: ...CHAPTER 12 Quality of Service Attaching a Policy Map to a Port 268 ...
Page 368: ...CHAPTER 14 Security Measures DHCP Snooping 368 ...
Page 422: ...CHAPTER 15 Basic Administration Protocols Remote Monitoring 422 ...
Page 488: ...CHAPTER 17 IP Configuration Setting the Switch s IP Address IP Version 6 488 ...
Page 538: ...CHAPTER 20 IP Services Forwarding UDP Service Requests 538 ...
Page 594: ...CHAPTER 21 Unicast Routing Configuring the Open Shortest Path First Protocol Version 2 594 ...
Page 624: ...CHAPTER 22 Multicast Routing Configuring PIMv6 for IPv6 624 ...
Page 638: ...CHAPTER 23 Using the Command Line Interface CLI Command Groups 638 ...
Page 712: ...CHAPTER 26 SNMP Commands 712 ...
Page 720: ...CHAPTER 27 Remote Monitoring Commands 720 ...
Page 776: ...CHAPTER 29 Authentication Commands Management IP Filter 776 ...
Page 876: ...CHAPTER 34 Port Mirroring Commands Local Port Mirroring Commands 876 ...
Page 898: ...CHAPTER 37 Address Table Commands 898 ...
Page 998: ...CHAPTER 41 Quality of Service Commands 998 ...
Page 1060: ...CHAPTER 42 Multicast Filtering Commands MLD Proxy Routing 1060 ...
Page 1078: ...CHAPTER 43 LLDP Commands 1078 ...
Page 1088: ...CHAPTER 44 Domain Name Service Commands 1088 ...
Page 1164: ...CHAPTER 47 IP Interface Commands IPv6 to IPv4 Tunnels 1164 ...
Page 1260: ...CHAPTER 48 IP Routing Commands Open Shortest Path First OSPFv3 1260 ...
Page 1304: ...SECTION IV Appendices 1304 ...
Page 1310: ...APPENDIX A Software Specifications Management Information Bases 1310 ...
Page 1343: ...DG GS4826S DG GS4850S E012011 R02 F1 2 2 0 ...
Page 1344: ......