Cisco Cisco ASR 5000
SGSN Service Configuration Procedures
Configuring the DNS Client Context for APN and SGW Resolution (Optional) ▀
SGSN Administration Guide, StarOS Release 18 ▄
Configuring the DNS Client Context for APN and SGW
Resolution (Optional)
This section describes how to configure the context from which DNS client has to be selected for performing an APN
FQDN query for resolving a PGW address (S4-SGSN) or a co-located PGW / GGSN address (Gn SGSN), and the
context from which DNS client has to be selected for performing an RAI FQDN query for resolving an SGW address
(S4-SGSN).
FQDN query for resolving a PGW address (S4-SGSN) or a co-located PGW / GGSN address (Gn SGSN), and the
context from which DNS client has to be selected for performing an RAI FQDN query for resolving an SGW address
(S4-SGSN).
By default, the S4-SGSN supports the initiation of a DNS query after APN selection using a S-NAPTR query for EPC-
capable subscribers. The S4-SGSN resolves a PGW/GGSN by sending an APN-FQDN query to the DNS client.
Similarly, the S4-SGSN resolves the SGW by sending a RAI-FQDN query to the DNS client. The DNS Client then
sends a query to the DNS server to retrieve NAPTR/SRV/A records and return the SGW or PGW IP address to the
SGSN.
capable subscribers. The S4-SGSN resolves a PGW/GGSN by sending an APN-FQDN query to the DNS client.
Similarly, the S4-SGSN resolves the SGW by sending a RAI-FQDN query to the DNS client. The DNS Client then
sends a query to the DNS server to retrieve NAPTR/SRV/A records and return the SGW or PGW IP address to the
SGSN.
Important:
For non-EPC capable subsribers, the S4-SGSN initiates only a DNS A query.
The Gn SGSN supports selecting a co-located PGW/GGSN node for EPC capable UEs by performing a DNS SNAPTR
lookup for APN FQDN for the service parameter”x-3gpp-pgw:x-gn" / "x-3gpp-pgw:x-gp”. Note that in addition to
these parameters, the service parameters In addition to these interfaces "x-3gpp-ggsn:x-gn" & "x-3gpp-ggsn:x-gp"
are used for selecting standalone GGSNs.
lookup for APN FQDN for the service parameter”x-3gpp-pgw:x-gn" / "x-3gpp-pgw:x-gp”. Note that in addition to
these parameters, the service parameters In addition to these interfaces "x-3gpp-ggsn:x-gn" & "x-3gpp-ggsn:x-gp"
are used for selecting standalone GGSNs.
For performing a DNS SNAPTR query, the SGSN requires an additional, optional, configuration that identifies the
context where DNS lookup for EPC-capable UEs must occur. This is accomplished by creating a call-control-profile
that specifies the context from which the DNS client should be used for resolving a co-located PGW/GGSN address on
a Gn SGSN as well.
context where DNS lookup for EPC-capable UEs must occur. This is accomplished by creating a call-control-profile
that specifies the context from which the DNS client should be used for resolving a co-located PGW/GGSN address on
a Gn SGSN as well.
Use the following procedure to configure and associate the configure DNS for APN resolution to support S4
functionality:
functionality:
Step 1
Access Call Control Profile Configuration Mode and create a call control profile.
Step 2
Configure the DNS client context to resolve PGW UEs via the context the DNS client is configured.
Step 3
Configure the DNS client context to resolve SGW UEs via the context where the DNS client is configured.
Example Configuration
config
call-control-profile <name>
dns-pgw context <dns_client_context_name>
dns-sgw context <dns_client_context_name>
end
Notes:
dns-pgw context is valid for selecting a PGW (in an S4-SGSN) as well as a co-located PGW/GGSN (in a Gn
SGSN). If the interface selected for a UE is S4 and if there is no dns-pgw context configured under the Call