What is the full form of GGSN

introduction

This document describes a scenario that occurs on the Cisco 5x00 Series Aggregated Services Router (ASR) acting as a GGSN (Gateway General Packet Radio Service) Support Node (GPRS) that is out of new call policy, as well as some Precautions to be taken when designing the Domain Name System (DNS) network to avoid service outages.

Supported by Parthasarathy M and Anthony Fajri, Cisco TAC Engineers.

Problem: Configuring DNS service parameters when refusing new call policy on GGSN

With GGSN software upgrades becomes the New Call Policy applied to GGSN to avoid the service degradation for subscribers. The server is expected to send GPRS Support Node (SGSN) traffic to the next available GGSNs according to the new calling policy.

However, in some cases this is not the caseRejection of the calling policy did not work as expected and the service degradation is detected when updating the procedure.

solution

How does policy rejection for new calls work?

As soon as the Policy for the call again is applied to GGSN,

[local] ASR5K_LAB # newcall policy ggsn-service all reject

GGSN rejects the new incoming Create Packet Data Protocol (PDP) Context Request (CPC-R) in which no resource is availableso that SGSN can select the next available GGSN. In this way, the service disruption at the time of the maintenance window for the update is minimized.

New Call Policy Laboratory Result:

SGSN configuration:

In this example the Rejection of New Call Guidelines applied to GGSN1. When the call comes in, the SGSN sends the CPC request to GGSN1, which in turn rejects the call, and then the SGSN sends the request to GGSN2.

Monitoring of the subscriber trace output:

===> GPRS Mobility / Session Management Message (2 bytes) Protocol Discriminator: GMM message Message: Attach Complete INBOUND >>>>> 05: 34: 35: 320 Eventid: 88112 (0) ===> GPRS Mobility / Session Management Message (34 Bytes) Protocol Discriminator: SM message Message: Activate PDP Context Request Requested NSAPI Requested LLC SAPI Requested Qos Length of Qos: 14 Requested PDP address Length: 2 Access Point Name Length: 10 <<<< OUTBOUND 05:34: 35: 323 Eventid: 116004 (3) GTPC Tx PDU, from 192.168.2.2:19002 to 192.168.2. Access Point Name: sitt1.com GSN Address I: 0xC0A80202 (192.168.2.2) GSN Address II: 0xC0A80203 (192.168.2.3) MSISDN: 128612345678901 QOS Profile: 0x0223421F72967373440DFFFF00 COMMON FLAGS FOLLOW: Prohibicit Payload Service Type: Multicit MB Service Compression: Procedures Ready: no MBMS Counting Information: no No QoS negotiation: no NRSN: yes Upgrade QoS Supported: no Dual Address Bearer Flag: no COMMON FLAGS END. Radio Access Technology: GERAN MS Time Zone: -4: 00 Daylight Saving Time: +1 hour INFORMATION ELEMENTS END. INBOUND >>>>> 05: 34: 35: 326 Eventid: 116003 (3) GTPC Rx PDU, from 192.168.2.1:2123 to 192.168.2.INFORMATION ELEMENTS FOLLOW: Cause: 0xC7 (GTP_NO_RESOURCES_AVAILABLE) INFORMATION ELEMENTS END. <<<< OUTBOUND 05: 34: 35: 327 Eventid: 116004 (3) GTPC Tx PDU, from 192.168.2.2:19002 to 192.168.2. Access Point Name: sitt1.com GSN Address I: 0xC0A80202 (192.168.2.2) GSN Address II: 0xC0A80203 (192.168.2.3) MSISDN: 128612345678901 QOS Profile: 0x0223421F72967373440DFFFF00 COMMON FLAGS FOLLOW: Prohibicit Payload Service Type: Multicit MB Service Compression: Procedures Ready: no MBMS Counting Information: no No QoS negotiation: no NRSN: yes Upgrade QoS Supported: no Dual Address Bearer Flag: no COMMON FLAGS END. Radio Access Technology: GERAN MS Time Zone: -4: 00 Daylight Saving Time: +1 hour INFORMATION ELEMENTS END. INBOUND >>>>> 05: 34: 35: 337 Eventid: 116003 (3) GTPC Rx PDU, from 192.168.2.128:2123 to 192.168.2.INFORMATION ELEMENTS FOLLOW: Cause: 0x80 (GTP_REQUEST_ACCEPTED) Reorder Required: 0x0 (Not present) Tunnel ID Data I: 0x0FFFFFF8 Tunnel ID Control I: 0x0FFFFFF8 Charging ID: 0x00000007 END USER ADDRESS FOLLOWS: PDP Type Organization: IETF PDP Type Number: IPv4 IPv4 Address: 12.0.0.6 END USER ADDRESS ENDS. GSN Address I: 0xC0A80280 (192.168.2.128) GSN Address II: 0xC0A80280 (192.168.2.128) QOS Profile: 0x0222421F7296D1FE460D03FE004A4A INFORMATION ELEMENTS END.

How does SGSN choose the GGSN?


Under the apn-profile configuration there is the command apn-solution-dns-query snaptr.

apn-solution-dns-query snaptr [epc-ue | non-epc-ue]

SNAPTR filter based on the EPC function of the user equipment (UE). Use this command to enable SNAPTR type DNS query for APN resolution for 3G subscribers with EPC subscription. The configuration in this mode promotes the control of this function per APN.
If none of the keywords is contained in the configuration, the S-NAPTR query applies to all UEs, both for EPC-capable UE and for non-EPC-capable UE. This function is not activated by default.

This means that SGSN sends the DNS query in Name Authority Pointer (NAPTR) format (sitt1.com.apn.epc.mnc090.mcc262.3gppnetwork.org) to select the GGSN.

If the NAPTR query fails, the SGSN fallback is reset to query type A (sitt1.mnc045.mcc123.gprs) to get the GGSN IP address.

Laboratory result:

SGSN configuration:

apn-profile default

    apn-resolve-dns-query snaptr

Monitor log tracking:

*** Verbosity Level (2) *** *** Verbosity Level (3) *** <<<< OUTBOUND 05: 42: 24: 667 Eventid: 5957 (3) DNS PDU Tx from: 192.168.2.1: 49351 to: 192.168.1.254: 53 bytes: 76 Query ID: 6366 Type: Query Question: NAPTR? sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org. Additional: Name:. Ext-RCODE: 0 Type: OPT UDPsize: 4096 INBOUND >>>>> 05: 42: 24: 750 Eventid: 5956 (3) DNS PDU Rx from: 192.168.1.254: 53 to: 192.168.2.1: 49351 bytes: 76 Query ID: 6366 Type: Response Authoritative Answer: No Response code: ServFail Question: NAPTR? sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org. Additional: Name:. Ext-RCODE: 0 Type: OPT UDPsize: 4096 <<<< OUTBOUND 05: 42: 24: 752 Eventid: 5957 (3) DNS PDU Tx from: 192.168.2.1: 51619 to: 192.168.1.254: 53 bytes: 57 Query ID: 16777 Type: Query Question: A? sitt1.com.MNC045.MCC123.GPRS. Additional: Name:. Ext-RCODE: 0 Type: OPT UDPsize: 4096 INBOUND >>>>> 05: 42: 24: 781 Eventid: 5956 (3) DNS PDU Rx from: 192.168.1.254: 53 to: 192.168.2.1: 51619 bytes: 57 Query ID: 16777 Type: Response Authoritative Answer: No Response code: Success Question: A? sitt1.com.MNC045.MCC123.GPRS. Additional: Name:. Ext-RCODE: 0 Type: OPT UDPsize: 4096

Example configuration

When DNS is configured with the following service parameters:

Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp


When a non-EPC capable UE tries to establish a connection, the SGSN decided to resort to a query based on the service type of the DNS response.

Example:

SGSN checks the DNS answer service type, and if the keyword x-3gpp-ggsn: x-gn and x-3gpp-ggsn: x-gp cannot be found, the SGSN fallback is carried over to the A query type.

Query Name: sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org Answer: Order: 10 Preference: 10 Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x -gn: x-gp Regular Expression: Replacement: TOPON.S5.GGSN1.NODES.EPC.MNC090.MCC262.3GPPNETWORK.ORG Query Name: sitt1.mnc045.mcc123.gprs Query Type: A TTL: 48993 seconds Answer: IP Address : 192.168.2.1


For example, if you only configure a single GGSN IP address for a record in the DNS, the SGSN will not be able to redirect to the next available GGSNs, which will affect the service.

As in the SGSN Administrator Guide:


The Gn SGSN supports and supports the selection of a packet data network (PDN) gateway (P-GW) / GGSN node for EPC-capable UEs located at the same location and performs a DNS straight-forward NAPTR (SNAPTR) search for the fully qualified one APN Domain Name (FQDN) for the service parameter x-3gpp-pw through.:x-gn / x-3gpp-pgw: x-gp. The interfaces in the service parameters x-3gpp-ggsn: x-gn and x-3gpp-ggsn: x-gp are also used to select standalone GGGSNs.


So when you design the DNS records you can use service parameters like:
Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp


DNS then returns several gateway addresses (GW) for non-EPC-capable UE.

Query Name: sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org
Query Type: NAPTR TTL: 42755 seconds
Answer:
Order: 40 Preference: 40
Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp
Regular Expression:
Replacement: TOPON.S5.GGSN03.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG

Query Name: sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org
Query Type: NAPTR TTL: 42755 seconds
Answer:
Order: 10 Preference: 10
Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp
Regular Expression:
Replacement: TOPON.S5.GGSN02.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG

Query Name: sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org
Query Type: NAPTR TTL: 42755 seconds
Answer:
Order: 20 Preference: 20
Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp
Regular Expression:
Replacement: TOPON.S5.GGSN05.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG

Query Name: sitt1.com.apn.epc.mnc045.mcc123.3gppnetwork.org
Query Type: NAPTR TTL: 42755 seconds
Answer:
Order: 30 Preference: 30
Flags: A Service: x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp
Regular Expression:
Replacement: TOPON.S5.GGSN04.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG

Query Name: TOPON.S5.GGSN04.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG
Query Type: NAPTR TTL: 48993 seconds
Answer:
IP Address: 192.168.2.22

Query Name: TOPON.S5.GGSN03.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG
Query Type: NAPTR TTL: 48993 seconds
Answer:
IP Address: 192.168.2.18

Query Name: TOPON.S5.GGSN05.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG
Query Type: NAPTR TTL: 48993 seconds
Answer:
IP Address: 192.168.2.23

Query Name: TOPON.S5.GGSN02.NODES.EPC.mnc045.mcc123.3GPPNETWORK.ORG
Query Type: NAPTR TTL: 48993 seconds
Answer:
IP Address: 192.168.2.21

Together, make sure your DNS is like x-3gpp-pgw: x-s5-gtp: x-s8-gtp: x-gn: x-gp: x-3gpp-ggsn: x-gn: x-gp configured to avoid service degradation when you have multiple GGSNs to support geo-redundancy.