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IP Routing
19-8
19
Address Resolution Protocol
If IP routing is enabled (page 19-4), 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.
Table 19-1 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 8926EM
Страница 6: ...ii ...
Страница 34: ...Getting Started ...
Страница 44: ...Introduction 1 10 1 ...
Страница 62: ...Initial Configuration 2 18 2 ...
Страница 64: ...Switch Management ...
Страница 76: ...Configuring the Switch 3 12 3 ...
Страница 118: ...Basic Management Tasks 4 42 4 ...
Страница 164: ...User Authentication 6 28 6 ...
Страница 176: ...Access Control Lists 7 12 7 ...
Страница 284: ...Quality of Service 14 8 14 ...
Страница 294: ...Multicast Filtering 15 10 15 ...
Страница 300: ...Domain Name Service 16 6 16 ...
Страница 310: ...Dynamic Host Configuration Protocol 17 10 17 ...
Страница 320: ...Configuring Router Redundancy 18 10 18 ...
Страница 344: ...IP Routing 19 24 19 ...
Страница 356: ...Unicast Routing 20 12 20 Web Click Routing Protocol RIP Statistics Figure 20 5 RIP Statistics ...
Страница 386: ...Unicast Routing 20 42 20 ...
Страница 388: ...Command Line Interface ...
Страница 400: ...Overview of the Command Line Interface 21 12 21 ...
Страница 466: ...SNMP Commands 24 16 24 ...
Страница 520: ...Access Control List Commands 26 18 26 ...
Страница 546: ...Rate Limit Commands 30 2 30 ...
Страница 612: ...VLAN Commands 34 24 34 ...
Страница 626: ...Class of Service Commands 35 14 35 ...
Страница 670: ...DHCP Commands 39 16 39 ...
Страница 716: ...IP Interface Commands 41 36 41 ...
Страница 768: ...IP Routing Commands 42 52 42 ...
Страница 770: ...Appendices ...
Страница 791: ......
Страница 792: ...20 Mason Irvine CA 92618 Phn 949 679 8000 www smc com 150200062800A R02 149100000035A R01 SMC8926EM SMC8950EM ...