The network element must have DNS servers defined if it is configured as a client resolver.

From Perimeter Router Security Technical Implementation Guide Cisco

Part of DNS servers must be defined for client resolver.

SV-15330r2_rule The network element must have DNS servers defined if it is configured as a client resolver.

Vulnerability discussion

The susceptibility of IP addresses to spoofing translates to DNS host name and IP address mapping vulnerabilities. For example, suppose a source host wishes to establish a connection with a destination host and queries a DNS server for the IP address of the destination host name. If the response to this query is the IP address of a host operated by an attacker, the source host will establish a connection with the attackers host, rather than the intended target. The user on the source host might then provide logon, authentication, and other sensitive data.

Check content

Review the device configuration to ensure that DNS servers have been defined if it has been configured as a client resolver (name lookup). The configuration should look similar to one of the following examples: ip domain-lookup ip name-server or no ip domain-lookup The first configuration example has DNS lookup enabled and hence has defined its DNS server. The second example has DNS lookup disabled. Note: ip domain-lookup is enabled by default. Hence it may not be shown—depending on the IOS release. If it is enabled, it will be shown near the beginning of the configuration.

Fix text

Configure the device to include DNS servers or disable domain lookup.

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