Appendix G Command Interpreter
P-791R v2 User’s Guide
328
ARP Behavior and the ARP ackGratuitous Commands
The ZyXEL Device does not accept ARP reply information if the ZyXEL Device did not send
out a corresponding request. This helps prevent the ZyXEL Device from updating its ARP
table with an incorrect IP address to MAC address mapping due to a spoofed ARP. An
incorrect IP to MAC address mapping in the ZyXEL Device’s ARP table could cause the
ZyXEL Device to send packets to the wrong device.
Commands for Using or Ignoring Gratuitous ARP Requests
A host can send an ARP request to resolve its own IP address. This is called a gratuitous ARP
request. The packet uses the host’s own IP address as the source and destination IP address.
The packet uses the Ethernet broadcast address (FF:FF:FF:FF:FF:FF) as the destination MAC
address. This is used to determine if any other hosts on the network are using the same IP
address as the sending host. The other hosts in the network can also update their ARP table IP
address to MAC address mappings with this host’s MAC address.
The
ip arp ackGratuitous
commands set how the ZyXEL Device handles gratuitous
ARP requests.
• Use
ip arp ackGratuitous active no
to have the ZyXEL Device ignore gratuitous
ARP requests.
• Use
ip arp ackGratuitous active yes
to have the ZyXEL Device respond to
gratuitous ARP requests.
For example, say the regular gateway goes down and a backup gateway sends a gratuitous
ARP request. If the request is for an IP address that is not already in the ZyXEL Device’s
ARP table, the ZyXEL Device sends an ARP request to ask which host is using the IP
address. After the ZyXEL Device receives a reply from the backup gateway, it adds an
ARP table entry.
If the ZyXEL Device’s ARP table already has an entry for the IP address, the ZyXEL
Device’s response depends on how you configure the
ip arp ackGratuitous
forceUpdate
command.
• Use
ip arp ackGratuitous forceUpdate on
to have the ZyXEL Device
update the MAC address in the ARP entry.
• Use
ip arp ackGratuitous forceUpdate off
to have the ZyXEL Device not
update the MAC address in the ARP entry.
A backup gateway (as in the following graphic) is an example of when you might want to turn
on the forced update for gratuitous ARP requests. One day gateway A shuts down and the
backup gateway (B) comes online using the same static IP address as gateway A. Gateway B
broadcasts a gratuitous ARP request to ask which host is using its IP address. If ackGratuitous
is on and set to force updates, the ZyXEL Device receives the gratuitous ARP request and
updates its ARP table. This way the ZyXEL Device has a correct gateway ARP entry to
forward packets through the backup gateway. If ackGratuitous is off or not set to force
updates, the ZyXEL Device will not update the gateway ARP entry and cannot forward
packets through gateway B.
Содержание P-791R
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Страница 7: ...Safety Warnings P 791R v2 User s Guide 7 This product is recyclable Dispose of it properly...
Страница 8: ...Safety Warnings P 791R v2 User s Guide 8...
Страница 20: ...Table of Contents P 791R v2 User s Guide 20...
Страница 32: ...32...
Страница 46: ...Chapter 2 Introducing the Web Configurator P 791R v2 User s Guide 46...
Страница 53: ...Chapter 3 Wizard Setup for Internet Access P 791R v2 User s Guide 53...
Страница 54: ...Chapter 3 Wizard Setup for Internet Access P 791R v2 User s Guide 54...
Страница 58: ...Chapter 4 Point to point Configuration P 791R v2 User s Guide 58...
Страница 59: ...59 PART II Network Setup WAN Setup 61 LAN Setup 83 Network Address Translation NAT Screens 93...
Страница 60: ...60...
Страница 82: ...Chapter 5 WAN Setup P 791R v2 User s Guide 82...
Страница 104: ...Chapter 7 Network Address Translation NAT Screens P 791R v2 User s Guide 104...
Страница 105: ...105 PART III Security Filter 107...
Страница 106: ...106...
Страница 110: ...110...
Страница 114: ...Chapter 9 Static Route P 791R v2 User s Guide 114...
Страница 118: ...Chapter 10 Dynamic DNS Setup P 791R v2 User s Guide 118...
Страница 128: ...Chapter 11 Remote Management Configuration P 791R v2 User s Guide 128...
Страница 140: ...Chapter 12 Universal Plug and Play UPnP P 791R v2 User s Guide 140...
Страница 141: ...141 PART V Maintenance System 143 Logs 149 Tools 153 Diagnostic 159...
Страница 142: ...142...
Страница 148: ...Chapter 13 System P 791R v2 User s Guide 148...
Страница 158: ...Chapter 15 Tools P 791R v2 User s Guide 158...
Страница 162: ...162...
Страница 168: ...Chapter 17 Introducing the SMT P 791R v2 User s Guide 168...
Страница 172: ...Chapter 18 General Setup P 791R v2 User s Guide 172...
Страница 178: ...Chapter 19 WAN Setup P 791R v2 User s Guide 178...
Страница 194: ...Chapter 22 Remote Node Setup P 791R v2 User s Guide 194...
Страница 198: ...Chapter 23 Static Route Setup P 791R v2 User s Guide 198...
Страница 226: ...Chapter 25 Filter Configuration P 791R v2 User s Guide 226...
Страница 228: ...Chapter 26 SNMP Configuration P 791R v2 User s Guide 228...
Страница 230: ...Chapter 27 System Password P 791R v2 User s Guide 230...
Страница 240: ...Chapter 28 System Information Diagnosis P 791R v2 User s Guide 240...
Страница 268: ...Chapter 31 IP Routing Policy Setup P 791R v2 User s Guide 268...
Страница 272: ...Chapter 32 Schedule Setup P 791R v2 User s Guide 272...
Страница 278: ...Chapter 33 Troubleshooting P 791R v2 User s Guide 278...
Страница 280: ...280...
Страница 285: ...Appendix A Product Specifications P 791R v2 User s Guide 285 Figure 194 Masonry Plug and M4 Tap Screw...
Страница 286: ...Appendix A Product Specifications P 791R v2 User s Guide 286...
Страница 320: ...Appendix E IP Address Assignment Conflicts P 791R v2 User s Guide 320...
Страница 324: ...Appendix F Common Services P 791R v2 User s Guide 324...
Страница 330: ...Appendix G Command Interpreter P 791R v2 User s Guide 330...
Страница 342: ...Appendix H Log Descriptions P 791R v2 User s Guide 342...
Страница 348: ...Appendix J Legal Information P 791R v2 User s Guide 348...
Страница 354: ...Appendix S Customer Support P 791R v2 User s Guide 38...