Overview: Using caching to improve DNS performance
You can configure a DNS cache on the BIG-IP system to allow the system to
more quickly respond to repeated DNS queries. You can configure a simple DNS cache or a DNS cache
with more advanced resolving and validation functions. There are three types of DNS cache
configurations available on the BIG-IP system: a transparent cache, a resolver cache, and a
validating resolver cache.
Typically, you configure a resolver cache where the BIG-IP system either acts as the LDNS for
clients or is in the LDNS resolver path for clients. By caching DNS responses and answering
queries from the cache, the BIG-IP system is able to immediately respond to subsequent client
requests for the same resource. This enhances DNS performance in two significant ways. First,
answering a DNS query from the cache is faster and has a very short latency, because the sooner a
client gets a DNS response, the faster the client can access the Internet resource. Secondly,
caching DNS responses reduces the number of queries that have to be resolved. The BIG-IP system
uses the cache to resolve the same query from multiple clients handling many more queries per
second than a typical DNS resolver.
About the transparent DNS cache
You can configure a transparent cache on the BIG-IP system to use
external DNS resolvers to resolve queries, and then cache the responses from the resolvers. The
next time the system receives a query for a response that exists in the cache, the system
immediately returns the response from the cache. The transparent cache contains messages and
resource records.
A
transparent cache
in the BIG-IP system consolidates content that would otherwise
be cached across multiple external resolvers. When a consolidated cache is in front of external
resolvers (each with their own cache), it can produce a much higher cache hit percentage.
F5 Networks recommends that you configure the BIG-IP system to forward queries, which cannot be
answered from the cache, to a pool of local DNS servers rather than the local BIND instance
because BIND performance is slower than using multiple external resolvers.
For systems using the DNS Express™ feature, the BIG-IP system first processes the requests through DNS
Express, and then caches the responses.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
About the resolver DNS cache
You can configure a resolver cache on the BIG-IP system to resolve DNS
queries and cache the responses. The next time the system receives a query for a response that
exists in the cache, the system returns the response from the cache. The
resolver
cache
contains messages, resource records, and the nameservers the system queries to
resolve DNS queries.
It is important for network architects to note that it is possible to configure the local BIND
instance on the BIG-IP system to act as an external DNS resolver. However,
F5 Networks does not recommend this approach, because the performance of BIND is slower than
using a resolver cache.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
About the validating resolver DNS cache
You can configure a validating resolver cache on the BIG-IP system to
recursively query public DNS servers, validate the identity of the DNS server sending the
responses, and then cache the responses. The next time the system receives a query for a response
that exists in the cache, the system returns the DNSSEC-compliant response from the cache. The
validating resolver
cache contains messages, resource records, the nameservers the
system queries to resolve DNS queries, and DNSSEC keys.
Using the validating resolver cache, the BIG-IP system mitigates cache poisoning by validating
DNS responses using DNSSEC validation. This is important, because attackers can attempt to
populate a DNS cache with erroneous data that redirects clients to fake web sites, or downloads
malware and viruses to client computers. When an authoritative server signs a DNS response, the
validating resolver verifies the data before entering the data into the cache. Additionally, the
validating resolver cache includes a built-in filter and detection mechanism that rejects
unsolicited DNS responses.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
About information
stored in DNS caches
The transparent, resolver, and validating resolver DNS caches contain a
message cache and a resource record cache. The resolver and validating resolver DNS caches also
contain a nameserver cache. Additionally, the validating resolver cache contains a key cache.
Message cache
The message cache contains the entire contents of a particular DNS
response including the supporting records.
Resource Record cache
The resource record cache contains the individual record elements in the
DNS response, which may include an SOA record, DNSSEC key records, glue records, and other
supporting records.
Nameserver cache
The nameserver cache contains information about the public DNS
nameservers the resolver has used to fill the cache. Often there is more than one nameserver
that is listed as an authority for a zone; therefore, the cache entries track metrics for the
nameservers so that the system can send new queries to the best nameserver. The cache entries
include metrics, such as time to live (TTL), round trip times (RRT), and properties, such as
EDNS support and zone lameness.
Key cache
The key cache contains the DNSKEY resource records and tracks the DNSSEC
keys for use in DNSSEC validation. This cache also contains information about the validity of
the DNSSEC keys.
Configuring DNS
cache global settings
Configure the global settings on the BIG-IP system
to specify how the system manages the DNS caches you create.
On the Main tab, click
DNS
Settings
Caches
.
In the
Minimum TTL
field, type the minimum number of seconds you
want the system to cache DNS resource records.
When you configure this setting the system can cache resource records longer
than the owner of the records intended.
In the
Maximum TTL
field, type the number of seconds after which you
want the system to re-query for resource records.
With this setting, the system can re-query for resource records sooner
than the owner of the records intended.
In the
EDNS Buffer Size
field, type the number of bytes you want the
system to advertise as the EDNS buffer size in UDP queries.
The default value for EDNS is
4096
bytes.
Click
Update
.
After you configure the DNS global settings,
create at least one DNS cache.
Overview: Caching responses from external
resolvers
You can configure a transparent cache on the BIG-IP system to use
external DNS resolvers to resolve queries, and then cache the responses from the resolvers. The
next time the BIG-IP system receives a query for a response that exists in the cache, the system
immediately returns the response from the cache. The transparent cache contains messages and
resource records.
A
transparent cache
in the BIG-IP system consolidates content that would otherwise
be cached across multiple external resolvers. When a consolidated cache is in front of external
resolvers (each with their own cache), it can produce a much higher cache hit percentage.
F5 Networks
recommends that you configure the BIG-IP system to forward queries, which cannot be answered from
the cache, to a pool of local DNS servers rather than the local BIND instance because BIND
performance is slower than using multiple external resolvers.
For systems using the DNS Express™ feature, the BIG-IP system first processes the requests through DNS
Express, and then caches the responses.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
BIG-IP system using transparent
cache
Creating a transparent DNS cache
Create a transparent cache on the BIG-IP system when you want
the system to cache DNS responses from external DNS resolvers.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click
Create
.
The New DNS Cache screen opens.
In the
Name
field, type a name for the cache.
From the
Resolver Type
list, select
Transparent
.
Click
Finished
.
Associate the DNS cache with a custom DNS profile.
Enabling transparent DNS caching
Ensure that at least one transparent cache exists on the BIG-IP
system.
To enable the BIG-IP system to cache responses to DNS queries, create a custom DNS
profile and associate it with a transparent DNS cache.
On the Main tab, click
DNS
Delivery
Profiles
DNS
or
Local Traffic
Profiles
Services
DNS
.
The DNS profile list screen opens.
Click
Create
.
The New DNS Profile screen opens.
In the
Name
field, type a unique name for the profile.
In the General Properties area, from the
Parent Profile
list, accept the default
dns
profile.
Select the
Custom
check box.
In the DNS Features area, from the
Use BIND Server on BIG-IP
list, select
Disabled
.
In the DNS Features area, from the
DNS Cache
list, select
Enabled
.
When you enable the
DNS Cache
option, you must also select a DNS cache from the
DNS Cache Name
list.
In the DNS Features area, from the
DNS Cache Name
list, select the DNS cache that you want to associate with this profile.
You can associate a DNS cache with a profile, even when the
DNS
Cache
option, is
Disabled
.
Click
Finished
.
Assign the custom DNS profile to the virtual server or listener that handles the
DNS traffic from which you want to cache responses.
Assigning a custom
DNS profile to an LTM virtual server
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a virtual server
when you want the BIG-IP system to perform DNS caching on traffic that the virtual
server handles.
This task applies only to LTM-provisioned systems.
On the Main tab, click
Local Traffic
Virtual Servers
.
The Virtual Server List
screen opens.
Click the name of the virtual server you want to
modify.
From the
Configuration
list, select
Advanced
.
From the
DNS Profile
list, select the
custom DNS profile you created.
Click
Update
to save the
changes.
The responses to DNS queries handled by this virtual server are cached on the BIG-IP
system.
Assigning a custom
DNS caching profile to a BIG-IP DNS listener
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a listener when you
want the BIG-IP system to perform DNS caching on traffic that the listener handles.
This task applies only to DNS-provisioned systems.
On the Main tab, click
DNS
Delivery
Listeners
.
The Listeners List screen opens.
Click the name of the listener you want to modify.
In the Service area, from the
DNS Profile
list, select a
custom DNS profile configured for DNS caching.
Click
Update
.
Creating a custom DNS monitor
Create a custom DNS monitor to send DNS queries, generated using the settings you
specify, to a pool of DNS servers and validate the DNS responses.
When defining values for custom monitors, make sure you avoid using any values that
are on the list of reserved keywords. For more information, see
SOL
3653
(for version 9.0 systems and later) on the AskF5 technical support web site at
www.askf5.com
.
On the Main tab, click
DNS
Delivery
Load Balancing
Monitors
or
Local Traffic
Monitors
.
The Monitor List screen opens.
Click
Create
.
The New Monitor screen opens.
In the
Name
field, type a name for the monitor.
From the
Type
list, select
DNS
.
In the
Query Name
field, type the domain name that you
want the monitor to query.
For the zone,
siterequest.com
, you might want the
monitor to query for
www.siterequest.com
.
Configure additional settings based on your network requirements.
Click
Finished
.
Creating a pool of local DNS servers
Ensure that at least one custom DNS monitor exists on the BIG-IP system. Gather the IP addresses of the DNS servers that you want to
include in a pool to which the BIG-IP system load balances DNS traffic.
Create a pool of local DNS servers when you want to load balance DNS queries to
other DNS servers.
On the Main tab, click the applicable path.
DNS
Delivery
Load Balancing
Pools
Local Traffic
Pools
The Pool List screen opens.
Click
Create
.
The New Pool screen opens.
In the
Name
field, type a unique name for the pool.
For the
Health Monitors
setting, from the
Available
list, select the custom DNS monitor you created and move the monitor to the
Active
list.
Using the
New Members
setting, add each resource that you want to include in the pool:
(Optional) In the
Node Name
field, type a name for the node portion of the pool member.
In the
Address
field, type an IP address.
In the
Service Port
field, type a port number, or select a service name from the list.
(Optional) In the
Priority
field, type a priority number.
Click
Add
.
Click
Finished
.
Determining DNS
cache performance
Ensure
that you have first
created a DNS cache and associated it with a DNS profile, and have assigned
the profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view statistics to determine
how well a DNS cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing records in a DNS cache
You can view records in a DNS cache to determine how well a specific cache on the
BIG-IP system is performing.
Log in to the command-line interface of the BIG-IP system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, type the command:
show ltm dns cache records rrset cache
<cache name>
For example, the command:
show ltm dns cache records rrset cache
my_transparent_cache
, displays the resource
records in the cache named
my_transparent_cache
.
Viewing DNS cache statistics
Ensure that you have created a DNS cache and a DNS profile and have assigned the
profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view DNS cache statistics to determine how well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing
DNS cache statistics
using the
GUI
You can view DNS cache statistics to determine how
well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
Managing transparent cache size
Determine the amount of memory the BIG-IP system has and how
much of that memory you want to commit to DNS caching. View the statistics for a cache
to determine how well the cache is working.
You can change the size of a DNS cache to fix cache performance issues.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the
Message Cache Size
field, type the maximum size in bytes
for the DNS message cache.
The BIG-IP system caches the messages in a DNS response in the message cache. A higher
maximum size makes it possible for more DNS responses to be cached and increases the cache
hit percentage. A lower maximum size forces earlier eviction of cached content, but can
lower the cache hit percentage.
When you change the value of the
Message Cache Size
, the records in the message cache are
automatically removed. If you do not want to clear the message cache, do not change the
value of this parameter.
In the
Resource Record Cache Size
field, type the maximum size
in bytes for the DNS resource record cache.
The BIG-IP system caches the supporting records in a DNS response in the Resource
Record cache. A higher maximum size makes it possible for more DNS responses to be cached
and increases the cache hit percentage. A lower maximum size forces earlier eviction of
cached content, but can lower the cache hit percentage.
When you
change the value of the
Resource Record Cache Size
, the records
in the resource record cache are automatically removed from the cache. If you do not
want to clear the resource record cache, do not change the value of this parameter.
In the
Nameserver Cache Count
field, type the maximum number of
DNS nameservers for which the BIG-IP system caches connection and
capability data.
When you change the value of the
Nameserver Cache
Count
, the records in the nameserver cache are automatically removed from
the cache. If you do not want to clear the nameserver cache, do not change the value of
this parameter.
Click
Finished
.
Clearing a DNS
cache
You can clear all records from a specific DNS
cache on the BIG-IP system.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
On the menu bar, click
Statistics
.
The Local Traffic Statistics screen opens.
Select the check box next to the cache you want to clear, and then click
Clear Cache
.
Clearing groups of
records from a DNS cache
You can clear groups of records of a specific type
from a DNS cache by resizing the cache that contains those records.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the DNS Cache area, to clear specific records from the cache, do one of the
following:
To clear messages from the cache:
change the value in the
Message Cache Size
field.
To clear resource records from the cache:
change the value in the
Resource Record Cache Size
field.
To clear nameservers from the cache:
change the value in the
Name Server Cache Count
field.
To clear DNSSEC keys from the cache:
change the value in the
DNSSEC Key Cache Size
field.
Click
Update
.
The BIG-IP system clears the records in the caches that you resized.
Clearing specific
records from a DNS cache using tmsh
You can clear specific records from a DNS cache
using
tmsh
. For example, you can delete
all RRSET records or only the A records in the specified cache.
In
tmsh
, you can use the command
completion feature to discover the types of records that are available for
deletion.
Log in to the command-line interface of the BIG-IP
system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, to navigate to
the directory that contains the DNS cache records, type the command:
ltm dns cache records
To delete specific DNS cache records, type a
variation of this command:
delete
<cache-type>
type
<record-type>
cache
<cache-name>
For example, the command
delete rrset type a cache
my_resolver_cache
, deletes the A records from the
resource record cache of the resolver cache named
my_resolver_cache
.
Overview: Resolving queries and caching
responses
You can configure the BIG-IP system to resolve DNS queries and cache the
responses by creating a resolver DNS cache. The next time the BIG-IP system receives a query for
a response that exists in the cache, the system returns the response from the cache. The
resolver cache
contains messages, resource records, and the nameservers the system
queries to resolve DNS queries.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
BIG-IP system using resolver cache
Creating a resolver DNS cache
Create a resolver cache on the BIG-IP system when you want
the system to resolve DNS queries and cache responses.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click
Create
.
The New DNS Cache screen opens.
In the
Name
field, type a name for the cache.
From the
Resolver Type
list, select
Resolver
.
Click
Finished
.
Associate the DNS cache with a custom DNS profile.
Enabling resolving and caching
Ensure that at least one DNS cache exists on the BIG-IP system.
To enable the BIG-IP system to resolve DNS queries and cache the responses, create
a custom DNS profile and associate it with a resolver DNS cache.
On the Main tab, click
DNS
Delivery
Profiles
DNS
or
Local Traffic
Profiles
Services
DNS
.
The DNS profile list screen opens.
Click
Create
.
The New DNS Profile screen opens.
In the
Name
field, type a unique name for the profile.
Select the
Custom
check box.
In the DNS Features area, from the
Use BIND Server on BIG-IP
list, select
Disabled
.
In the DNS Features area, from the
DNS Cache
list, select
Enabled
.
When you enable the
DNS Cache
option, you must also select a DNS cache from the
DNS Cache Name
list.
In the DNS Features area, from the
DNS Cache Name
list, select the DNS cache that you want to associate with this profile.
You can associate a DNS cache with a profile, even when the
DNS
Cache
option, is
Disabled
.
Click
Finished
.
Assign the custom DNS profile to the virtual server or listener that handles the
DNS traffic.
Assigning a custom
DNS profile to an LTM virtual server
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a virtual server
when you want the BIG-IP system to perform DNS caching on traffic that the virtual
server handles.
This task applies only to LTM-provisioned systems.
On the Main tab, click
Local Traffic
Virtual Servers
.
The Virtual Server List
screen opens.
Click the name of the virtual server you want to
modify.
From the
Configuration
list, select
Advanced
.
From the
DNS Profile
list, select the
custom DNS profile you created.
Click
Update
to save the
changes.
The responses to DNS queries handled by this virtual server are cached on the BIG-IP
system.
Assigning a custom
DNS caching profile to a BIG-IP DNS listener
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a listener when you
want the BIG-IP system to perform DNS caching on traffic that the listener handles.
This task applies only to DNS-provisioned systems.
On the Main tab, click
DNS
Delivery
Listeners
.
The Listeners List screen opens.
Click the name of the listener you want to modify.
In the Service area, from the
DNS Profile
list, select a
custom DNS profile configured for DNS caching.
Click
Update
.
Determining DNS
cache performance
Ensure
that you have first
created a DNS cache and associated it with a DNS profile, and have assigned
the profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view statistics to determine
how well a DNS cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing records in a DNS cache
You can view records in a DNS cache to determine how well a specific cache on the
BIG-IP system is performing.
Log in to the command-line interface of the BIG-IP system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, type the command:
show ltm dns cache records rrset cache
<cache name>
For example, the command:
show ltm dns cache records rrset cache
my_transparent_cache
, displays the resource
records in the cache named
my_transparent_cache
.
Viewing DNS cache statistics
Ensure that you have created a DNS cache and a DNS profile and have assigned the
profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view DNS cache statistics to determine how well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing
DNS cache statistics
using the
GUI
You can view DNS cache statistics to determine how
well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
Managing cache size
Determine the amount of memory the BIG-IP system has and how
much you want to commit to DNS caching. View the statistics for a cache to determine how
well the cache is working.
You can change the size of a DNS cache to fix cache performance issues.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the
Message Cache Size
field, type the maximum size in bytes
for the DNS message cache.
The BIG-IP system caches the messages in a DNS response in the message cache. A higher
maximum size makes it possible for more DNS responses to be cached and increases the cache
hit percentage. A lower maximum size forces earlier eviction of cached content, but can
lower the cache hit percentage.
When you change the value of the
Message Cache Size
, the records in the message cache are
automatically removed. If you do not want to clear the message cache, do not change the
value of this parameter.
In the
Resource Record Cache Size
field, type the maximum size
in bytes for the DNS resource record cache.
The BIG-IP system caches the supporting records in a DNS response in the Resource
Record cache. A higher maximum size makes it possible for more DNS responses to be cached
and increases the cache hit percentage. A lower maximum size forces earlier eviction of
cached content, but can lower the cache hit percentage.
When you
change the value of the
Resource Record Cache Size
, the records
in the resource record cache are automatically removed from the cache. If you do not
want to clear the resource record cache, do not change the value of this parameter.
In the
Nameserver Cache Count
field, type the maximum number of
DNS nameservers for which the BIG-IP system caches connection and
capability data.
When you change the value of the
Nameserver Cache
Count
, the records in the nameserver cache are automatically removed from
the cache. If you do not want to clear the nameserver cache, do not change the value of
this parameter.
In the
Unsolicited Reply Threshold
field, change the default
value if you are using the BIG-IP system to monitor for unsolicited
replies using SNMP.
The system always rejects unsolicited replies. The default value of 0 (off) indicates
the system does not generate SNMP traps or log messages when rejecting unsolicited
replies. Changing the default value alerts you to a potential security attack, such as
cache poisoning or DOS. For example, if you specify 1,000,000 unsolicited replies, each
time the system receives 1,000,000 unsolicited replies, it generates an SNMP trap and log
message.
Click
Update
.
Clearing a DNS
cache
You can clear all records from a specific DNS
cache on the BIG-IP system.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
On the menu bar, click
Statistics
.
The Local Traffic Statistics screen opens.
Select the check box next to the cache you want to clear, and then click
Clear Cache
.
Clearing groups of
records from a DNS cache
You can clear groups of records of a specific type
from a DNS cache by resizing the cache that contains those records.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the DNS Cache area, to clear specific records from the cache, do one of the
following:
To clear messages from the cache:
change the value in the
Message Cache Size
field.
To clear resource records from the cache:
change the value in the
Resource Record Cache Size
field.
To clear nameservers from the cache:
change the value in the
Name Server Cache Count
field.
To clear DNSSEC keys from the cache:
change the value in the
DNSSEC Key Cache Size
field.
Click
Update
.
The BIG-IP system clears the records in the caches that you resized.
Clearing specific
records from a DNS cache using tmsh
You can clear specific records from a DNS cache
using
tmsh
. For example, you can delete
all RRSET records or only the A records in the specified cache.
In
tmsh
, you can use the command
completion feature to discover the types of records that are available for
deletion.
Log in to the command-line interface of the BIG-IP
system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, to navigate to
the directory that contains the DNS cache records, type the command:
ltm dns cache records
To delete specific DNS cache records, type a
variation of this command:
delete
<cache-type>
type
<record-type>
cache
<cache-name>
For example, the command
delete rrset type a cache
my_resolver_cache
, deletes the A records from the
resource record cache of the resolver cache named
my_resolver_cache
.
Overview: Resolving queries and caching validated responses
You can configure the BIG-IP system to recursively query public DNS
servers, validate the identity of the DNS server sending the responses, and then cache the
responses. You do this by configuring a validating resolver cache on the system. The next time
the BIG-IP system receives a query for a response that exists in the cache, the system returns
the DNSSEC-compliant response from the cache. The
validating resolver
cache contains
messages, resource records, the nameservers the system queries to resolve DNS queries, and DNSSEC
keys.
Using the validating resolver cache, the BIG-IP system mitigates cache poisoning by validating
DNS responses using DNSSEC validation. This is important, because attackers can attempt to
populate a DNS cache with erroneous data that redirects clients to fake web sites, or downloads
malware and viruses to client computers. When an authoritative server signs a DNS response, the
validating resolver verifies the data before entering the data into the cache. Additionally, the
validating resolver cache includes a built-in filter and detection mechanism that rejects
unsolicited DNS responses.
The DNS Cache feature is available only when the BIG-IP system is licensed
for DNS Services.
BIG-IP system using validating resolver
cache
Creating a validating resolver DNS cache
Create a validating resolver cache on the BIG-IP system when
you want the system to resolve DNS queries, use DNSSEC to validate the responses, and
cache the responses.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click
Create
.
The New DNS Cache screen opens.
In the
Name
field, type a name for the cache.
From the
Resolver Type
list, select
Validating
Resolver
.
Click
Finished
.
Associate the DNS cache with a custom DNS profile.
About SEP records and DNSSEC
Each DNSSEC zone has a list of read-only Security Entry Point (SEP) records. The BIG-IP
DNS creates these records
automatically when you create a zone. These SEP records consist of Delegation Signer (DS) and
DNSKEY records.
Obtaining a trust or DLV anchor
Determine the signed zones from which you want to obtain a trust or DLV
anchor.
If you want the BIG-IP system to cache a validated response
for the signed zones, you need to obtain a trust or DLV anchor.
On the Main tab, click
DNS
Zones
DNSSEC Zones
.
The DNSSEC Zone List screen opens.
Click the name of the DNSSEC zone for which you want to view or copy SEP records.
On the menu bar, click
SEP Records
.
The SEP records display for each generation of a key. If the SEP record screen
is unexpectedly blank, ensure that at least one data center and a server representing the
BIG-IP DNS device exist in the BIG-IP system configuration.
Copy the trust or DLV anchor from the
DNSKEY Record
field.
Adding a trust
anchor to a validating resolver DNS cache
Ensure that you have copied trust anchors for the signed zones that you want to add to
the validating resolver.
A validating resolver uses at least one trust
anchor to validate DNS responses.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Trust Anchors
.
The Trust Anchors screen opens.
Click the
Add
button.
In the
Trust Anchor
field, paste the trust anchor that you
copied from the signed zone.
The trust anchor must be specified in a string format.
Click
Finished
.
For each additional trust anchor that you want to
add to the validating resolver, repeat steps 4-6.
The validating resolver can now validate the
content of DNS responses from the zones for which you added trust anchors.
Adding a DLV anchor to a validating resolver DNS cache
Ensure that you have copied a DLV anchor for the signed zones that you want to add to
the validating resolver.
A validating resolver needs a DLV anchor to
validate DNS responses from outside a zone.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
DLV Anchors
.
The DLV Anchors screen opens.
Click the
Add
button.
In the
DLV Anchor
field, paste the DLV anchor that you want to
add to the validating resolver.
The DLV anchor must be specified in a string format.
Click
Finished
.
For each additional DLV anchor that you want to
add to the validating resolver, repeat steps 4-6.
The validating resolver can now validate the
content of DNS responses from the zones for which you added DLV anchors.
Enabling validating resolver DNS caching
Ensure that at least one DNS cache exists on the BIG-IP system.
To enable the BIG-IP system to validate the identity of the DNS servers returning
responses and then to cache those responses, create a custom DNS profile and associate
it with a validating resolver DNS cache.
On the Main tab, click
DNS
Delivery
Profiles
DNS
or
Local Traffic
Profiles
Services
DNS
.
The DNS profile list screen opens.
Click
Create
.
The New DNS Profile screen opens.
In the
Name
field, type a unique name for the profile.
In the General Properties area, from the
Parent Profile
list, accept the default
dns
profile.
Select the
Custom
check box.
In the DNS Features area, from the
Use BIND Server on BIG-IP
list, select
Disabled
.
In the DNS Features area, from the
DNS Cache
list, select
Enabled
.
When you enable the
DNS Cache
option, you must also select a DNS cache from the
DNS Cache Name
list.
In the DNS Features area, from the
DNS Cache Name
list, select the DNS cache that you want to associate with this profile.
You can associate a DNS cache with a profile, even when the
DNS
Cache
option, is
Disabled
.
Click
Finished
.
Assign the custom DNS profile to the virtual server that handles the DNS traffic
that includes the responses to queries that you want to cache.
Assigning a custom
DNS profile to an LTM virtual server
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a virtual server
when you want the BIG-IP system to perform DNS caching on traffic that the virtual
server handles.
This task applies only to LTM-provisioned systems.
On the Main tab, click
Local Traffic
Virtual Servers
.
The Virtual Server List
screen opens.
Click the name of the virtual server you want to
modify.
From the
Configuration
list, select
Advanced
.
From the
DNS Profile
list, select the
custom DNS profile you created.
Click
Update
to save the
changes.
The responses to DNS queries handled by this virtual server are cached on the BIG-IP
system.
Assigning a custom
DNS caching profile to a BIG-IP DNS listener
Ensure that at least one custom DNS profile that is configured for DNS caching exists
on the BIG-IP system.
Assign a custom DNS profile to a listener when you
want the BIG-IP system to perform DNS caching on traffic that the listener handles.
This task applies only to DNS-provisioned systems.
On the Main tab, click
DNS
Delivery
Listeners
.
The Listeners List screen opens.
Click the name of the listener you want to modify.
In the Service area, from the
DNS Profile
list, select a
custom DNS profile configured for DNS caching.
Click
Update
.
Determining DNS
cache performance
Ensure
that you have first
created a DNS cache and associated it with a DNS profile, and have assigned
the profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view statistics to determine
how well a DNS cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing records in a DNS cache
You can view records in a DNS cache to determine how well a specific cache on the
BIG-IP system is performing.
Log in to the command-line interface of the BIG-IP system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, type the command:
show ltm dns cache records rrset cache
<cache name>
For example, the command:
show ltm dns cache records rrset cache
my_transparent_cache
, displays the resource
records in the cache named
my_transparent_cache
.
Viewing DNS cache statistics
Ensure that you have created a DNS cache and a DNS profile and have assigned the
profile to either an LTM virtual server or a BIG-IP DNS listener.
You can view DNS cache statistics to determine how well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
In the Details column for a cache, click
View
to display
detailed information about the cache.
Viewing
DNS cache statistics
using the
GUI
You can view DNS cache statistics to determine how
well a specific cache on the BIG-IP system is performing.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
Information displays about the DNS caches.
Record type
Description
Queries
Total number of queries handled by the cache.
Responses
Total number of responses sent from the cache.
Answered Locally
Number of locally answered queries handled by the cache.
Using Nameservers
Number of nameservers using queries handled by the cache.
Managing cache size
Determine the amount of memory the BIG-IP system has and how
much you want to commit to DNS caching. View the statistics for a cache to determine how
well the cache is working.
You can change the size of a DNS cache to fix cache performance issues.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the
Message Cache Size
field, type the maximum size in bytes
for the DNS message cache.
The BIG-IP system caches the messages in a DNS response in the message cache. A higher
maximum size makes it possible for more DNS responses to be cached and increases the cache
hit percentage. A lower maximum size forces earlier eviction of cached content, but can
lower the cache hit percentage.
When you change the value of the
Message Cache Size
, the records in the message cache are
automatically removed. If you do not want to clear the message cache, do not change the
value of this parameter.
In the
Resource Record Cache Size
field, type the maximum size
in bytes for the DNS resource record cache.
The BIG-IP system caches the supporting records in a DNS response in the Resource
Record cache. A higher maximum size makes it possible for more DNS responses to be cached
and increases the cache hit percentage. A lower maximum size forces earlier eviction of
cached content, but can lower the cache hit percentage.
When you
change the value of the
Resource Record Cache Size
, the records
in the resource record cache are automatically removed from the cache. If you do not
want to clear the resource record cache, do not change the value of this parameter.
In the
Nameserver Cache Count
field, type the maximum number of
DNS nameservers for which the BIG-IP system caches connection and
capability data.
When you change the value of the
Nameserver Cache
Count
, the records in the nameserver cache are automatically removed from
the cache. If you do not want to clear the nameserver cache, do not change the value of
this parameter.
In the
Unsolicited Reply Threshold
field, change the default
value if you are using the BIG-IP system to monitor for unsolicited
replies using SNMP.
The system always rejects unsolicited replies. The default value of 0 (off) indicates
the system does not generate SNMP traps or log messages when rejecting unsolicited
replies. Changing the default value alerts you to a potential security attack, such as
cache poisoning or DOS. For example, if you specify 1,000,000 unsolicited replies, each
time the system receives 1,000,000 unsolicited replies, it generates an SNMP trap and log
message.
Click
Update
.
Clearing a DNS
cache
You can clear all records from a specific DNS
cache on the BIG-IP system.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
On the menu bar, click
Statistics
.
The Local Traffic Statistics screen opens.
Select the check box next to the cache you want to clear, and then click
Clear Cache
.
Clearing groups of
records from a DNS cache
You can clear groups of records of a specific type
from a DNS cache by resizing the cache that contains those records.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the DNS Cache area, to clear specific records from the cache, do one of the
following:
To clear messages from the cache:
change the value in the
Message Cache Size
field.
To clear resource records from the cache:
change the value in the
Resource Record Cache Size
field.
To clear nameservers from the cache:
change the value in the
Name Server Cache Count
field.
To clear DNSSEC keys from the cache:
change the value in the
DNSSEC Key Cache Size
field.
Click
Update
.
The BIG-IP system clears the records in the caches that you resized.
Clearing specific
records from a DNS cache using tmsh
You can clear specific records from a DNS cache
using
tmsh
. For example, you can delete
all RRSET records or only the A records in the specified cache.
In
tmsh
, you can use the command
completion feature to discover the types of records that are available for
deletion.
Log in to the command-line interface of the BIG-IP
system.
At the BASH prompt, type the command:
tmsh
At the
tmsh
prompt, to navigate to
the directory that contains the DNS cache records, type the command:
ltm dns cache records
To delete specific DNS cache records, type a
variation of this command:
delete
<cache-type>
type
<record-type>
cache
<cache-name>
For example, the command
delete rrset type a cache
my_resolver_cache
, deletes the A records from the
resource record cache of the resolver cache named
my_resolver_cache
.
Overview: Resolving queries for local zones with authoritative responses
You can configure a transparent, resolver, or validating resolver DNS cache with local zones.
Use this configuration when you want the BIG-IP system to resolve queries
for small local zones with authoritative responses.
For example, the network administrator at Site Request created a resolver DNS cache to handle
DNS traffic for
siterequest.com
. She configured the cache to provide
authoritative DNS responses to all domains on the Internet. Now, she wants to configure the cache
to serve authoritative responses to queries for the small local zone
wiki.siterequest.com
. When resolving DNS queries for
wiki.siterequest.com, the local zone effectively supercedes the cache.
Successful DNS query resolution from transparent local zone
Failed DNS query resolution from transparent local zone
About local
zones
A
local zone
contains resource records
that a DNS cache uses to resolve matching DNS queries with authoritative DNS responses. The
Type
attribute of the local zone
determines how the cache handles a DNS query that does not match the local zone.
Adding local zones
to a DNS cache
Ensure that at least one DNS cache is configured on the BIG-IP system.
Determine which local zones and associated resource records you
want the BIG-IP system to respond to with authoritative DNS responses.
Add a local zone to a DNS cache only when the zone
has a small resource record set.
If you want the
BIG-IP system to respond to DNS queries with authoritative DNS responses for a zone
with a large resource record set, instead create a DNS zone and enable DNS Express.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Local Zones
.
The Local Zones screen opens.
Click the
Add
button.
In the
Name
field, type the domain name of the local zone.
The domain you enter must be at the apex of the zone. For example, you
could name a local zone
siterequest.com
, and then add resource
records for the members
wiki.siterequest.com.
and
download.siterequest.com.
.
From the
Type
list, select how the cache handles a non-matching
query for the local zone.
The Description column provides a sample response to a query for
wiki.siterequest.com
, when the local zone is
siterequest.com.
Deny
For a non-matching query, the cache drops the DNS query.
This is an example
of a response to a non-matching query:
DNS request timed
out
Redirect
For a non-matching query, when the query is for a subdomain of the local zone,
the cache returns the same response that it would for the local zone. For example, if
you add the local zone
siterequest.com
, the cache returns the same
response to queries for
wiki.siterequest.com.
and
download.wiki.siterequest.com.
.
This is an example of a
response to a non-matching query:
NOERROR rcode returned and
example.com. NOT resolved as expected
Refuse
For a non-matching query, the cache returns a REFUSED message in the DNS
response.
This is an example of a response to a non-matching query:
REFUSED rcode returned and example.com. NOT resolved as
expected
Static
For a non-matching query, the cache returns a NoData or NXDOMAIN in the DNS
response, which also includes the SOA record if the local zone contains one.
This
is an example of a response to a non-matching query:
NOERROR rcode
returned and example.com. NOT resolved as expected
Transparent
Transparent
is the default value.
For a non-matching
query, the cache performs a pass-through or iterative resolution of the DNS query.
If the query matches, but no resource records are available, the cache returns a
response with a NoData message.
This is an example of a response to a
non-matching query:
NOERROR rcode returned and example.com. NOT
resolved as expected
Type Transparent
For a non-matching query, or a query for a matching domain name, but with a
request for a record of a different type, the cache performs a pass-through or
iterative resolution of the DNS query; however, if the query matches, but no resource
records are available, the cache does not return a response with a NoData message.
This is an example of a response to a non-matching query:
DNS
request resolved to example.com. as expected
In the Records area, in the field, specify a resource record to identify the local
zone, including domain name, type, class, TTL, and record data, separated by spaces, and
then click
Add
.
You can add multiple resource records.
This is an example of an A record entry:
wiki.siterequest.com. IN A
10.10.10.124
. This is an example of a AAAA record entry:
wiki.siterequest.com. IN AAAA 2002:0:1:12:123:c:cd:cdf
.
Click
Finished
.
Overview: Forwarding specific DNS queries to specific nameservers
You can configure a resolver or validating resolver DNS cache with forward zones. Do this
configuration when you want the BIG-IP system to forward DNS queries
that match the forward zones to specific nameservers, which resolve the query when the cache
does not contain a response.
For example, the network administrator for Site Request wants to configure the DNS cache to
resolve responses to queries for the zone:
app1.siterequest.com
.
She wants the responses to queries for this zone to be served from specific nameservers,
when the cache does not contain a response.
Successful DNS query resolution from forward zone
When a DNS cache configured with both local and forward zones receives a DNS
query, the system checks the local zones first. If the query does not match a local
zone, the system then checks the forward zones for a match.
About forward
zones
A DNS cache
forward zone
resolves
matching DNS queries by obtaining answers from one of the recursive nameservers associated with
the forward zone. When the BIG-IP system receives a
query that cannot be resolved from the cache, the system forwards the query to a nameserver
associated with the matching forward zone. When the nameserver returns a response, the BIG-IP
system caches the response, and returns the response to the resolver making the query.
Longest match
The BIG-IP system matches a DNS query with a forward zone based on longest
match. For example, the network administrator for Site Request, configures two forward zones.
download.siterequest.com.
is
configured with two nameservers with the IP addresses
172.27.5.1
and
172.27.7.247
.
app1.siterequest.com.
is configured with two
nameservers with the IP addresses
10.10.5.5
and
11.11.5.7
.
A query for
product.download.siterequest.com.
matches the forward zone
download.siterequest.com
and a query for
ftp.appl1.siterequest.com.
matches the forward
zone
app1.siterequest.com
.
Selecting a
nameserver
When a forward zone is configured with more than one nameserver, the BIG-IP
system forwards the first query to a randomly selected nameserver, and records the round trip
time (RTT) of a successful response. If the first nameserver does not return a response, the
BIG-IP system forwards the query to a different nameserver and records the RTT of a successful
response. After that, the system always sends a query to the nameserver with the fastest RTT. If
none of the nameservers return a response, or the RTT exceeds 120 seconds, the BIG-IP system
returns a
SERVFAIL
response
to the resolver making the query.
Adding forward
zones to a DNS cache
Ensure that at least one resolver DNS cache or validating resolver DNS cache exists in
the configuration.
Gather the IP addresses of the nameservers that
you want to associate with a forward zone.
When you want the BIG-IP system to forward queries
to specific nameservers for resolution and the cache does not contain a response to the
query, add a forward zone to a DNS cache.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Forward Zones
.
The Forward Zones screen opens.
Click the
Add
button.
In the
Name
field, type a name for the forward zone.
In the Nameservers area, in the
Address
field, type the IP
address of a DNS nameserver that the system considers authoritative for this zone, and
then click
Add
. Based on your network configuration, add IPv4 or
IPv6 addresses, or both.
The order of nameservers in the configuration does not impact which
nameserver the system selects to forward a query to.
Click
Finished
.
Deleting forward zones from a DNS cache
Determine which forward zone you want to delete.
When you no longer want the BIG-IP system to forward queries
to a forward zone, you can delete the forward zone.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Forward Zones
.
The Forward Zones screen opens.
Select the check box next to the forward zone you want to delete, and then click
Delete
.
A dialog box displays asking you to confirm the deletion.
Click
OK
to confirm the deletion.
Changing the
nameservers associated with a forward zone
Determine the forward zone that you want to modify.
Modify the nameservers that are associated with a
forward zone when you want the BIG-IP system to forward DNS queries for a matching
forward zone to a different set of nameservers.
On the Main tab, click
Local Traffic
DNS Caches
DNS Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Forward Zones
.
The Forward Zones screen opens.
Click the name of the forward zone you want to modify.
The properties screen opens.
In the Nameservers area, add or remove nameservers.
Click
Finished
.
Viewing statistics about DNS cache forward zones
Ensure that at least one DNS cache exists in the BIG-IP system
configuration.
You can view statistics about the queries and responses that a DNS cache forwards.
For example, to assess the reliability of a nameserver, you can view data about the
number of queries resolved by the nameserver within a specified timeframe.
On the Main tab, click
Statistics
Module Statistics
DNS
Caches
.
The DNS Caches Status Summary
screen opens.
From the
Statistics Type
list, select
Caches
.
In the Details column for a cache, click
View
to display
detailed information about the cache.
View the statistics in the Forwarder Activity
area.
Overview: Forwarding specific DNS queries to a pool of DNS servers
You can configure a resolver or validating resolver DNS cache with a forward zone that is
associated with a listener. The listener can load balance specific DNS queries to a pool of
DNS servers. For example, the network administrator for SiteRequest wants to configure the DNS
cache to resolve DNS queries for the forward zone
app2.siterequest.com
,
and wants the responses to be served from a pool of local DNS servers, when the cache does not
contain a response.
Successful DNS query resolution from pool of DNS servers associated with a forward
zone
Creating a custom DNS monitor
Create a custom DNS monitor to send DNS queries, generated using the settings you
specify, to a pool of DNS servers and validate the DNS responses.
When defining values for custom monitors, make sure you avoid using any values that
are on the list of reserved keywords. For more information, see
SOL
3653
(for version 9.0 systems and later) on the AskF5 technical support web site at
www.askf5.com
.
On the Main tab, click
DNS
Delivery
Load Balancing
Monitors
or
Local Traffic
Monitors
.
The Monitor List screen opens.
Click
Create
.
The New Monitor screen opens.
In the
Name
field, type a name for the monitor.
From the
Type
list, select
DNS
.
In the
Query Name
field, type the domain name that you
want the monitor to query.
For the zone,
siterequest.com
, you might want the
monitor to query for
www.siterequest.com
.
Configure additional settings based on your network requirements.
Click
Finished
.
Creating a pool of local DNS servers
Ensure that at least one custom DNS monitor exists on the BIG-IP system. Gather the IP addresses of the DNS servers that you want to
include in a pool to which the BIG-IP system load balances DNS traffic.
Create a pool of local DNS servers when you want to load balance DNS queries to
other DNS servers.
On the Main tab, click the applicable path.
DNS
Delivery
Load Balancing
Pools
Local Traffic
Pools
The Pool List screen opens.
Click
Create
.
The New Pool screen opens.
In the
Name
field, type a unique name for the pool.
For the
Health Monitors
setting, from the
Available
list, select the custom DNS monitor you created and move the monitor to the
Active
list.
Using the
New Members
setting, add each resource that you want to include in the pool:
(Optional) In the
Node Name
field, type a name for the node portion of the pool member.
In the
Address
field, type an IP address.
In the
Service Port
field, type a port number, or select a service name from the list.
(Optional) In the
Priority
field, type a priority number.
Click
Add
.
Click
Finished
.
Creating a resolver DNS cache
Create a resolver cache on the BIG-IP system when you want
the system to resolve DNS queries and cache responses.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click
Create
.
The New DNS Cache screen opens.
In the
Name
field, type a name for the cache.
From the
Resolver Type
list, select
Resolver
.
Click
Finished
.
Associate the DNS cache with a custom DNS profile.
Enabling resolving and caching
Ensure that at least one DNS cache exists on the BIG-IP system.
To enable the BIG-IP system to resolve DNS queries and cache the responses, create
a custom DNS profile and associate it with a resolver DNS cache.
On the Main tab, click
DNS
Delivery
Profiles
DNS
or
Local Traffic
Profiles
Services
DNS
.
The DNS profile list screen opens.
Click
Create
.
The New DNS Profile screen opens.
In the
Name
field, type a unique name for the profile.
Select the
Custom
check box.
In the DNS Features area, from the
Use BIND Server on BIG-IP
list, select
Disabled
.
In the DNS Features area, from the
DNS Cache
list, select
Enabled
.
When you enable the
DNS Cache
option, you must also select a DNS cache from the
DNS Cache Name
list.
In the DNS Features area, from the
DNS Cache Name
list, select the DNS cache that you want to associate with this profile.
You can associate a DNS cache with a profile, even when the
DNS
Cache
option, is
Disabled
.
Click
Finished
.
Assign the custom DNS profile to the virtual server or listener that handles the
DNS traffic.
Creating listeners that alert BIG-IP DNS to DNS queries for a pool of DNS servers
Ensure that a pool of DNS servers exists on DNS.
Configure a listener that alerts BIG-IP DNS to DNS queries destined for a pool of DNS
servers. The best practice is to create four listeners: one with an IPv4 address that
handles UDP traffic, and one with the same IPv4 address that handles TCP traffic; one
with an IPv6 address that handles UDP traffic, and one with the same IPv6 address that
handles TCP traffic.
If you have multiple BIG-IP DNS systems in a device
group, perform this procedure on only one system.
On the Main tab, click
DNS
Delivery
Listeners
.
The Listeners List screen opens.
Click
Create
.
The Listeners properties screen opens.
In the
Name
field, type a unique name for the
listener.
For the Destination setting, in the
Address
field, type
an IPv4 address on which BIG-IP DNS listens for network traffic.
From the
Listener
list, select
Advanced
.
For the
Address Translation
setting, select the
Enabled
check box.
In the Service area, from the
Protocol
list, select
UDP
.
From the
Default Pool
list, select the pool to which
this listener forwards DNS queries.
Click
Finished
.
Create another listener with the same IPv4
address and configuration, but select
TCP
from the
Protocol
list. Then, create two more listeners, configuring
both with the same IPv6 address, but one with the UDP protocol and one with the TCP
protocol.
Configuring a
forward zone with a listener that load balances DNS queries
Determine the DNS cache to which you want to add a forward zone. Ensure that a listener
that is associated with a pool of DNS servers is configured on the system.
When you want the BIG-IP DNS to forward DNS
queries to a pool of DNS servers, configure a forward zone with a nameserver that is a
listener, which load balances traffic to a pool of DNS servers.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
On the menu bar, click
Forward Zones
.
The Forward Zones screen opens.
Click the
Add
button.
In the
Name
field, type a name for the forward zone.
In the Nameservers area, in the
Address
field, type the IP
address of a DNS nameserver that the system considers authoritative for this zone, and
then click
Add
. Based on your network configuration, add IPv4 or
IPv6 addresses, or both.
The order of nameservers in the configuration does not impact which
nameserver the system selects to forward a query to.
Click
Finished
.
Depending upon your network configuration, add
additional listeners to the forward zone. The best practice is to associate four
listeners with the forward zone: one with an IPv4 address that handles UDP traffic, and
one with the same IPv4 address that handles TCP traffic; one with an IPv6 address that
handles UDP traffic, and one with the same IPv6 address that handles TCP traffic.
Overview: Customizing a DNS cache
You can customize a DNS cache on the BIG-IP system to meet specific
network needs by changing the default values on the DNS cache settings.
Resolving DNS queries for default local zones from a DNS cache
You can configure a DNS cache on the BIG-IP system to answer
DNS queries for default local zones.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
Select the
Enabled
check box for the
Answer Default
Zones
setting, when you want the BIG-IP system to
answer queries for the default zones: localhost, reverse 127.0.0.1 and ::1, and AS112
zones.
Click
Update
.
Using specific DNS servers as authoritative root nameservers
You can configure a resolver or validating resolver DNS cache on the BIG-IP system to use a specific server as an authoritative
nameserver for the DNS root nameservers.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the Root Hints area, in the
IP address
field, type the IP
address of a DNS server that the system considers authoritative for the DNS root
nameservers, and then click
Add
.
By default, the system uses the DNS root nameservers published by
InterNIC. When you add DNS root nameservers, the BIG-IP system no longer uses the
default nameservers published by InterNIC, but uses the nameservers you add as
authoritative for the DNS root nameservers.
Based on your network configuration, add IPv4 or IPv6 addresses or both.
Click
Update
.
Alerting the system
to cache poisoning
You can configure a resolver or validating
resolver DNS cache on the BIG-IP system to generate SNMP alerts and log messages when
the cache receives unsolicited replies. This is helpful as an alert to a potential
security attack, such as cache poisoning or DDoS.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the
Unsolicited Reply Threshold
field, change the default
value if you are using the BIG-IP system to monitor for unsolicited
replies using SNMP.
The system always rejects unsolicited replies. The default value of 0 (off) indicates
the system does not generate SNMP traps or log messages when rejecting unsolicited
replies. Changing the default value alerts you to a potential security attack, such as
cache poisoning or DOS. For example, if you specify 1,000,000 unsolicited replies, each
time the system receives 1,000,000 unsolicited replies, it generates an SNMP trap and log
message.
Click
Update
.
Configuring RRset
Rotate to specify the order to return resource records
You can configure the method the DNS cache uses on
the BIG-IP system when deciding the order to return resource records within cached
responses.
On the Main tab, click
DNS
Caches
Cache List
.
The DNS Cache List screen opens.
Click the name of the cache you want to modify.
The properties screen opens.
In the DNS Cache area, for the
RRSet Rotate
field, select one of
the following options:
Option
Description
none (default)
Returns resource records in the same order as received.
query id
Uses the query identification number to decide which resource record to set first.
The rotation methodology used is based on picking a random number to
select the first entry of the Resource Record Set (RRset). Local zones that are part of a Response Policy Zone
are not rotated.
