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350-801 · Question #196

A customer enters no IP domain lookup on the Cisco IOS XE gateway to suppress the interpreting of invalid commands as hostnames Which two commands are needed to restore DNS SRV or A record…

The correct answer is D. transport preferred none E. ip domain lookup. To restore DNS SRV or A record resolutions after no ip domain lookup was configured, the ip domain lookup command must be re-enabled, and transport preferred none must be set for DNS resolution to prioritize or allow DNS queries.

Voice Gateways and Session Border Controllers

Question

A customer enters no IP domain lookup on the Cisco IOS XE gateway to suppress the interpreting of invalid commands as hostnames Which two commands are needed to restore DNS SRV or A record resolutions? (Choose two.)

Options

  • Aip dhcp excluded-address
  • Bip dhcp-sip
  • Cip dhcp pool
  • Dtransport preferred none
  • Eip domain lookup

How the community answered

(45 responses)
  • A
    4% (2)
  • C
    2% (1)
  • D
    93% (42)

Why each option

To restore DNS SRV or A record resolutions after `no ip domain lookup` was configured, the `ip domain lookup` command must be re-enabled, and `transport preferred none` must be set for DNS resolution to prioritize or allow DNS queries.

Aip dhcp excluded-address

`ip dhcp excluded-address` configures a range of IP addresses that the DHCP server should not assign, unrelated to DNS resolution functionality.

Bip dhcp-sip

`ip dhcp-sip` is not a standard Cisco IOS command directly related to enabling general DNS resolution for SRV or A records.

Cip dhcp pool

`ip dhcp pool` configures a DHCP address pool on the gateway for client IP assignment and does not control the gateway's ability to perform DNS lookups itself.

Dtransport preferred noneCorrect

The `transport preferred none` command, often used in voice service configuration, allows the system to use DNS SRV records to determine the transport protocol, enabling proper resolution for SIP destinations. When set to `none`, it ensures DNS SRV is used and the transport is based on the DNS SRV response.

Eip domain lookupCorrect

The `ip domain lookup` command globally enables the DNS lookup feature on a Cisco IOS device, allowing it to resolve hostnames to IP addresses, which is essential for SRV and A record resolutions. Without this command, the gateway will not attempt DNS queries.

Concept tested: Cisco IOS DNS resolution configuration

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book/config-sip.html

Topics

#DNS Resolution#Cisco IOS XE#Voice Gateway Configuration#SRV Records

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