Table Of Contents

Restoring a Loopback Zone

Manually Configuring a Loopback Zone

Importing a BIND Loopback Zone File

Restoring a Loopback Zone

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A loopback zone is a reverse zone that enables a host to resolve the loopback address (127.0.0.1) to the name localhost. The loopback address is used by the host to enable it to direct network traffic to itself. You can configure a loopback zone manually or you can import it from an existing BIND zone file.

Name servers need this zone because no one has responsibility for network 127, yet systems use it for a loopback address. Since no one has direct responsibility, everyone who uses it is individually responsible for it. You could omit this zone and your name server would operate. However, a lookup of 127.0.0.1 might fail because the root name server contacted was not configured to map 127.0.0.1 to a name. Cisco recommends that you provide the mapping yourself.

Normally, you do not have to configure a loopback zone, because Cisco CNS Network Registrar automatically creates one for you. If, however, you accidentally delete the loopback zone, you can use the instructions in this appendix to create a new one.

Manually Configuring a Loopback Zone

To manually configure a lost loopback zone:

Using the CLI

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Step 1 Use the zone name create command to create a loopback zone.

This example adds the zone 127.in-addr.arpa, specifying that it is a primary zone, the name server is localhost, and the hostmaster is loopback:

nrcmd> zone 127.in-addr.arpa create primary localhost loopback 

Step 2 Use the zone name addRR command to add the pointer (PTR) resource record.

Although the zone command automatically creates the NS and SOA record for you, you need to use the addRR keyword to create a PTR record for the name server named in the ns field. This example adds the name 1.0.0, the type PTR, and the data localhost:

nrcmd> zone 127.in-addr.arpa addRR 1.0.0 PTR localhost 

Step 3 Use the zone name addRR command to add the Address (A) resource record.

The A record provides the name-to-address mapping for the zone. This example adds the name localhost, the type A, and the data 127.0.0.1:

nrcmd> zone 127.in-addr.arpa addRR localhost A 127.0.0.1 

Network Registrar automatically appends the zone name to the ns, person, and data fields; that is, localhost.127.in-addr.arpa and loopback.127.in-addr.arpa.

Step 4 Reload the DNS server.

nrcmd> dns reload 

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Importing a BIND Loopback Zone File

You can also create the loopback zone using a BIND format loopback zone file.

Using the CLI

Use the zone name create command to create a primary zone by importing an existing file that is in BIND format. This example adds the zone 127.in-addr.arpa, specifying that it is a primary zone and to import the BIND file, hosts.local:

nrcmd> zone 127.in-addr.arpa create primary file=hosts.local 

nrcmd> dns reload 

You can use this text to define the contents of the hosts.local file:

127.in-addr.arpa.43200 SOA localhost.127.in-addr.arpa.

loopback.127.in-addr.arpa. (

1 		;serial

3600		;refresh

3600		;retry

3600000		;expire

43200 )		;minim

127.in-addr.arpa.										IN		NS		localhost.127.in-addr.arpa.

1.0.0.127.in-addr.arpa.								86400		IN		PTR		localhost.127.in-addr.arpa.

localhost.127.in-addr.arpa.								86400		IN		A		127.0.0.1