Digi APPLICATION NOTE 34 - Manual (Page 9)

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2.4 Configure the Firewall
The firewall should be configured to monitor the ICMP requests generated by PPP 1. If the firewall detects
that 3 consecutive ICMP echo requests have failed, it will take PPP 1 out of service and deactivated thus
allowing PPP 4 to come up. The IP address in the firewall rule must be the IP address that PPP 1 is sending
pings to.
The recovery code will then test the ADSL connection before bringing it back into service. When the recovery
is successful and PPP 1 comes back into service, PPP 4 will be deactivated.
Configuration – Security > Firewall
Insert the following 2 rules:
Rule 1
pass out break end on ppp 1 proto icmp from any to 1.2.3.4 icmp-type echo
inspect-state oos 10 t=3 c=3 d=3 r=ping,10,5 rd=1 dt=1
Rule 2
Pass break end
Save the firewall rules by clicking the “Save (fw -> fw.txt)” button.
Rule 1 explained:
pass out break end on PPP 1 –
allow traffic outbound from PPP 1
proto icmp from any to 1.2.3.4 icmp-type echo – allow pings out to 1.2.3.4