BACKUP ACTIVATION
The backup service is executed by properly combining the commands:
set backup <options>
set trigger backup <options>
SET BACKUP COMMAND
The command set backup defines the criteria in order to verify the availability of the primary
connection, while the command set trigger backup programs the actions to execute when Imola
enters in backup status (i.e. when Imola detects that the primary connection is not available), and
the actions to execute when Imola comes back from backup status (i.e. when the primary
connection is available again).
Availability of the primary connection is verified by using one of the following criteria. Each criterion
has a precise form of the set backup command:
1. Periodic transmission of an ICMP echo request (ping packet) towards a specified IP address
through a specified network interface. The required command is:
set backup checking-ipaddress a.b.c.d via icmp through-interface <ifname>
The primary connection is unavailable if no ICMP echo reply is received after N attempts of
transmission. The number of attempts, the latency for the reply, the interval between a group of
attempts and the following one, are configured by using the commands:
set backup check-retries N
set backup check-wait T1
set backup check-interval T2
The sequence of ICMP packets is still transmitted on the specified interface and the primary
connection is available as soon as a reply is received. By using the command:
set backup check-tos N
It is possible to specify the value of the field Type of Service (TOS) of transmitted packets.
It is possible to define a list of interfaces on which verification is executed, by using the command:
set backup checking-ipaddress a.b.c.d via icmp through-interface <ifn1,ifn2 .. ifnN>
In this case the ICMP packets are sent to the address a.b.c.d by using ifn1 interface, in case of
failure the ifn2 interface is used. The primary connection is unavailable if the IP address is not
accessible from any of the specified interfaces.
It is possible to define a list of IP addresses to which ICMP packets are sent:
set backup checking-one-of-ipaddr-list ip1,ip2, …ipN via icmp through-interface <ifname>
In this case backup is activated if none of the addresses in the list replies to ICMP commands.
In this case too, it is possible to specify a list of interfaces:
set backup checking-one-of-ipaddr-list ip1,ip2, …ipN via icmp through-interface ifn1,ifn2
Through ifn1 interface, attempts are executed in order to reach one of the addresses in the list. If
there is no reply, the ifn2 interface is used and so on.
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