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101 · Question #384

In the current version of BIG-IP, what happens if the GTM does not find a wide IP that matches the DNS request?

The correct answer is E. It sends the request to an external DNS. When BIG-IP GTM receives a DNS query that does not match any configured wide IP, it forwards the request to a configured external DNS server for resolution rather than returning an error.

Section 2: F5 Solutions and Technology

Question

In the current version of BIG-IP, what happens if the GTM does not find a wide IP that matches the DNS request?

Options

  • AIt sends a broadcast request to all GTM devices.
  • BIt uses iQuery to request the information from LTM.
  • CIt sends a request to its configured backup GTM device.
  • DIt sends an un-resolvable error to the client.
  • EIt sends the request to an external DNS.

How the community answered

(34 responses)
  • A
    6% (2)
  • B
    9% (3)
  • C
    3% (1)
  • D
    3% (1)
  • E
    79% (27)

Why each option

When BIG-IP GTM receives a DNS query that does not match any configured wide IP, it forwards the request to a configured external DNS server for resolution rather than returning an error.

AIt sends a broadcast request to all GTM devices.

GTM does not broadcast DNS requests to all GTM devices; broadcasting is not a supported or efficient DNS resolution mechanism in BIG-IP DNS.

BIt uses iQuery to request the information from LTM.

iQuery is the proprietary protocol used for metric and status communication between BIG-IP devices and is not used to resolve unmatched DNS queries.

CIt sends a request to its configured backup GTM device.

GTM does not have a configured backup GTM device concept for delegating unmatched wide IP lookups; that is not how GTM failover or delegation works.

DIt sends an un-resolvable error to the client.

GTM does not return an unresolvable error for queries that lack a matching wide IP; it delegates those queries to an external DNS server instead.

EIt sends the request to an external DNS.Correct

BIG-IP GTM is configured with an external DNS server as a fallback resolver. When no wide IP matches the incoming query, GTM forwards the request to that external DNS server, allowing it to act as a transparent DNS proxy for names outside its managed scope. This behavior ensures clients receive a valid DNS response for non-GTM-managed names instead of a failure.

Concept tested: BIG-IP GTM DNS fallback to external DNS server

Source: https://techdocs.f5.com/en-us/bigip-14-1-0/big-ip-dns-implementations/configuring-gtm-to-use-bind-as-a-back-end-dns-server.html

Topics

#GTM#DNS resolution#wide IP#external DNS fallback

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