Default APN for DNS
With Release 18.2, it is possible for the operator to configure the MME
to use a default APN in some situations where the DNS resolution fails due to a
problem with the subscriber-requested APN. As a result, the Attach could
proceed or the PDP context activation could complete.
The Default APN for
DNS Failure feature makes it possible for the operator to ensure that calls and
PDP context activation are not rejected because of possible UE errors, such as,
the UE requested a misspelled APN name. This feature allows the operator to
promote activation success if
- the subscriber-requested APN
is not present in the subscription record,
- the wildcard subscription is
present in the subscription record.
is configured with the use of the
require-dns-fail-wildcard keyword. This keyword is
currently supported only on MME.
By default, this new
functionality is not enabled. If not enabled, then the MME sends a PDN
connectivity reject to the eNodeB if the DNS resolution fails for the reasons
Operator Policy - Default APN for DNS Failure is configured
with the commands in the APN Remap Table configuration mode which is a key
component of the Operator Policy feature. For information about this feature,
see the chapter on
How It Works
With the Default APN
for DNS Failure enabled by configuring the 'required-dns-fail-wildcard', if DNS
resolution fails because the UE-requested APN name is not present in the
subscription record but the wildcard subscription is present, then MME
overrides the requested APN with a configured default APN. The MME proceeds
with the DNS resolution of the configured default APN and then proceeds with
the Attach or PDP context activation.
The MME checks the
subscription record with the configured default APN. If subscription record of
the configured default APN is available, then the MME takes the QoS profile and
the ARP values from that record. If the subscription record is not available,
then the MME checks the QoS profile and ARP values included in the wildcard
Note that DNS
query will be retried with default APN only once. If DNS resolution fails
again, even after applying the configured default APN, then the Activation
Request will be rejected.
The graphic below
illustrates the intenal procedure the MME follows to determine if a default APN
should be used.
Figure 1. Decision
Tree for MME Using Default APN
The Default APN for
DNS Failure feature complies with the following standards:
- 3GPP TS 23.060
- 3GPP TS 36.413
- 3GPP TS 24.301
- 3GPP TS 29.274
- 3GPP TS 23.401
APN for DNS Failure
Enabling Default APN
for DNS Failure is configured in the APN Remap Table configuration mode. This
mode generates a remap table that is a key component of the Operator Policy
feature. The operator policy must be assigned subscribers in the LTE Policy,
the LTE policy's subscriber map must be associated with the MME service.
Check the MME's
current configuration for names of already created APN remap tables, operator
policies, subscriber maps and mme-service instances. If desired, these names
can be used to create associations
tables, policies and services.
We recommend that
all table, policy, and service names be unique - not only within a context but
across the MME's configuration. Do not use preconfigured names unless the
association is desired.
procedure will take you through all of the following:
- creating an APN remap table
and enabling 'require-dns-fail-wildcard',
- creating an operator policy
and associating the remap table with the operator policy,
- associating the remap table
with the operator policy,
- assigning subscribers to the operator
policy in the LTE policy,
- associating the LTE policy's
subscriber map to the MME service configuration.
keywords, and variables are defined in the
Interface Reference for this release.
All components must
be completed for the feature to be enabled. Begin this procedure in the Local
context in the Exec mode.
configuration components deals with creating an APN Remap Table and configuring
the special keyword specific to enabling the Default APN for DNS Failure
apn-remap-table <table_name> -noconfirm
apn-selection-default network-identifier net_id require-dns-fail-wildcard
- Specifies the network identifier to be used as the
default APN name. Must be a string of 1 to 62 characters, including digits,
letters, dots (.) and dashes (-).
- The keyword that enables the use of the default APN when
DNS resolution fails. This keyword is currently supported only on MME.
prefixed to the command will remove the
require-dns-fail-wildcard configuration from the remap table.
Associating the APN Remap Table with the Operator Policy
The following configuration components deals with creating an operator
policy or accessing the operator policy configuration to associate the APN
remap table identified in the configuration procedure above.
operator-policy name <policy_name> -noconfirm
associate apn-remap-table <table_name>
Assigning Subscribers to the Operator Policy
The following configuration components deals with assigning
subscribers to the operator policy in the LTE policy.
subscriber-map <map_name> -noconfirm
precedence precedence match-criteria all operator-policy-name <policy_name>
Subscriber's Map with the MME Service
configuration components deals with associating the LTE policy's subscriber map
to the MME service configuration
context context_name -noconfirm
mme-service <srvc_name> -noconfirm
associate subscriber-map <map_name>
show apn-remap-table full
command generates a display that indicates the
configuration for the APN Remap Table. The
APN when DNS Query fails field indicates if the Default APN for DNS
Failure feature has been enabled.
The following is a
sample display is only a portion of the output and this sample shows
configured as the default APN name.
show apn-remap-table full all
APN Remap Table Name = test-table
Default APN : star.com
Require Subscription APN : Not Configured
Use Default APN when no APN is requested : Yes
Use Default APN when DNS Query fails : Yes
Fallback APN to use when Default APN not present
in subscription : Not Configured
. . . .