Device's Default DNS Fallback Sequence

The device has a default DNS fallback sequence which is used if you don't configure customized DNS fallback policies in the DNS Fallback Policy table (see Configuring DNS Fallback Policy).

The device's default DNS fallback sequence for choosing which DNS server to query for DNS resolution depends on traffic type (IPv4 or IPv6) and is as follows:

■

IPv4 traffic:

a.

(Call Routing Only) The device checks the Internal DNS table or Internal SRV table for a matching FQDN and queries the corresponding DNS server (see Configuring the Internal DNS Table). If no matching FQDN is found, the device proceeds to the next DNS fallback priority (below).

b.

The device queries the DNS server of the associated IP Interface configured in the IP Interfaces table (see Configuring IP Network Interfaces).

c.

If no DNS server is configured for the associated IP Interface (or DNS failure occurs), the device queries the DNS server of the default IPv4 OAMP ("O+M+C") IP Interface.

d.

If no DNS server is configured for the default OAMP IP Interface (or DNS failure occurs), the device queries the default IPv4 DNS servers (see Configuring Default DNS Servers).

■

IPv6 traffic:

a.

The device queries the DNS server of the associated IP Interface configured in the IP Interfaces table (see Configuring IP Network Interfaces).

b.

If no DNS server is configured for the associated IP Interface (or DNS failure occurs), the device queries the DNS server of the default IPv6 OAMP ("O+M+C_6") IP Interface.

c.

If no DNS server is configured for the default IPv6 OAMP IP Interface (or DNS failure occurs), the device queries the DNS server of the default IPv4 OAMP ("O+M+C") IP Interface.

d.

If no DNS server is configured for the default IPv4 OAMP IP Interface, the device queries the default IPv6 DNS servers (see Configuring Default DNS Servers).

e.

If there are no default IPv6 DNS servers, the device queries the default IPv4 DNS servers (see Configuring Default DNS Servers).