Specifications

Chapter 4. Configuring Special Features 105
The router determines your gateway and/or DNS address implicitly via a means such as DHCP, static
configuration, PPP negotiation, etc.
If you specify more than one address to ping, you may want to assign the addresses to groups. Each group can be
assigned its own ping interval, number of samples, and success rate. For example, you might want the success rate
for the DNS address to be at least 95%, while a success rate of 50% would be reasonable for a heavily used
website. You can also disable and re-enable ping addresses by group. A group is identified by its number (0
through 65535).
To add an address to the ping list, use this command:
system backup add <ipaddr> | GW | DNS [<group>]
To remove an address from the ping list, use this command:
system backup delete <ipaddr> | GW | DNS [<group>]
To remove a group of addresses, enter:
system backup delete all [<group>]
To clear the ping list of all addresses, enter:
system backup delete all all
Ping Interval, Number of Samples, and Success Rate
By default, the router pings the addresses every 5 seconds until it has pinged each address 6 times; it requires a
minimum success rate of 50%. However, you can change the ping interval, number of samples, and success rate
for an address group using these commands:
system backup pinginterval <seconds> [<group>]
system backup pingsamples <samples> [<group>]
system backup successrate <percentage> [<group>]
Note: To disable a group of ping addresses, specify 0 for any of its three valuesÑ pinginterval, pingsamples, or
success rate.
The same ping interval, number of samples, and success rate apply to all addresses assigned to a group. (Any
address not assigned to a group is considered to belong to group 0.) All groups are tested in parallel. As soon as
any group fails its success rate test, the DSL link is assumed to have failed and the switchover to the backup is
performed.
During the ping test, every address in a group contributes to the current success rate of the group; as soon as the
current success rate falls below the minimum success rate, the group has failed. For example, if the minimum
success rate is 50% and the sample number is 6, the maximum sample size for a three-address group is 18 (6 times
3); thus, as soon as the group accumulates 10 failures (one more than 9 failures, which is 50% of 18), the group
fails.
DSL Restoration Retry Period
Once DSL link failure is determined, the router uses its console port as a serial port and data traffic is sent and
received through the V.90 modem connected to that port. This backup port continues to be used until it is time to