Cisco GGSN Release 8.0 Configuration Guide, Cisco IOS Release 12.4(15)XQ

Configuring Load Balancing on the GGSN

This chapter describes how to configure a gateway GPRS support node (GGSN) to support load balancing functions using the Cisco IOS software Server Load Balancing (SLB) feature. GTP load balancing provides increased reliability and availability when you are using multiple Cisco GGSNs or non-Cisco GGSNs in your GPRS/UMTS network.

For a complete description of the GGSN commands in this chapter, refer to the Cisco GGSN Command Reference for the Cisco GGSN release you are using. For a complete description of the other Cisco IOS SLB commands in this chapter, refer to the IOS Server Load Balancing feature module.

To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

This chapter includes the following sections:

•Overview of GTP Load Balancing

•Configuring GTP Load Balancing

•Monitoring and Maintaining the Cisco IOS SLB Feature

•Configuration Examples

Overview of GTP Load Balancing

This section provides an overview of the Cisco IOS SLB feature and GTP load balancing support on the GGSN. It includes the following sections:

•Overview of Cisco IOS SLB

•Overview of GTP Load Balancing

•GTP SLB Restrictions

Overview of Cisco IOS SLB

The Cisco SLB feature is an IOS-based solution that provides IP server load balancing. Using the Cisco IOS SLB feature, you can define a virtual server that represents a group of real servers in a cluster of network servers known as a server farm. In this environment, the clients connect to the IP address of the virtual server. When a client initiates a connection to the virtual server, the Cisco IOS SLB feature chooses a real server for the connection, based on a configured load-balancing algorithm.

The Cisco IOS SLB feature also provides firewall load balancing, which balances flows across a group of firewalls called a firewall farm.

Figure 13-1 presents a logical view of a simple Cisco IOS SLB network.

Figure 13-1 Logical View of IOS SLB

Overview of GTP Load Balancing

Cisco IOS SLB provides GGSN GTP load balancing and increased reliability and availability for the GGSN. GGSN GTP load balancing supports a subset of the overall server load-balancing functions that are available in the Cisco IOS SLB feature. Therefore, the full scope of Cisco IOS SLB functions is not applicable to the general packet radio service/Universal Mobile Telecommunication System (GPRS/UMTS) environment. For more information about unsupported functions, see the "GTP SLB Restrictions" section.

When configuring GTP load balancing, a pool of GGSNs is configured as a server farm in Cisco IOS SLB. These are the GGSNs across which you want to load-balance GTP sessions. A virtual server instance is configured in Cisco IOS SLB to load balance GTP sessions across the GGSN farm. This virtual server is associated with the server farm that you configured in Cisco IOS SLB.

When configuring GTP load balancing, note the following:

•GTP load balancing is supported by using the Cisco IOS SLB feature on the supervisor engine.

•The IOS SLB on the supervisor engine processes only the create PDP context requests sent to the GGSN virtual IP address. When a create PDP context request is received, a real GGSN is selected based on the load at that time. Once the PDP context has been established, all subsequent transactions corresponding to the PDP contexts occurs directly between that GGSN and corresponding SGSN, bypassing the Cisco IOS SLB on the supervisor engine.

•Additionally:

–Multiple virtual servers are supported

–Load-balanced real servers can be internal or external to the Cisco 7600 chassis

–Each virtual server must have one unique public IP address that is reachable from the SGSNs

–Each virtual server can correspond to one or more APNs.

–The DNS server used by the SGSNs to resolve the APNs to a GGSN IP address should use the GGSN virtual IP address.

Supported GTP Load Balancing Types

The Cisco IOS SLB supports two types of GTP load balancing:

•GTP Load Balancing Without GTP Cause Code Inspection

•GTP Load Balancing With GTP Cause Code Inspection

GTP Load Balancing Without GTP Cause Code Inspection

GTP load balancing without GTP cause code inspection enabled is recommended for Cisco GGSNs. It has the following characteristics:

•Can operate in dispatched mode or in directed server Network Address Translation (NAT) mode, but not in directed client NAT mode. In dispatched mode, the GGSNs must be Layer 2-adjacent to the Cisco IOS SLB device.

•Does not support stateful backup.

•Delivers tunnel creation messages destined to the virtual GGSN IP address to one of the real GGSNs, using the weighted round-robin load-balancing algorithm. See the "Weighted Round-Robin" section for more information about this algorithm.

•Requires Dynamic Feedback Protocol (DFP) to account for GTPv1 secondary PDP contexts.

GTP Load Balancing With GTP Cause Code Inspection

GTP load balancing with GTP cause code inspection enabled allows Cisco IOS SLB to monitor all PDP context signaling flows to and from server farms. This enables Cisco IOS SLB to monitor GTP failure cause codes, detecting system-level problems in both Cisco and non-Cisco GGSNs.

Table 13-1 lists the Create PDP Context response cause codes and the corresponding actions taken by Cisco IOS SLB.

GTP load balancing with GTP cause code inspection enabled has the following characteristics:

•Must operate in directed server NAT mode.

•Assigns PDP context creates from a specific International Mobile Subscriber ID (IMSI) to the same GGSN, or, if GTP APN-aware load balancing is configured, to the same server farm.

•Supports stateful backup.

•Tracks the number of open PDP contexts for each GGSN or APN, which enables server farms to use the weighted least connections (leastconns) algorithm for GTP load balancing. See the "Weighted Least Connections" section for more information about this algorithm.

•Enables Cisco IOS SLB to deny access to a virtual GGSN if the carrier code of the requesting IMSI does not match a specified value.

•Enables Cisco IOS SLB to support secondary PDP contexts, even without DFP.

Cisco IOS SLB Algorithms Supported for GTP Load Balancing

The following two Cisco IOS SLB algorithms are supported for GTP load balancing:

•Weighted Round-Robin

•Weighted Least Connections

Weighted Round-Robin

The weighted round- robin algorithm specifies that the real server used for a new connection to the virtual server is chosen from the server farm in a circular fashion. Each real server is assigned a weight, n, that represents its capacity to handle connections, as compared to the other real servers associated with the virtual server. That is, new connections are assigned to a given real server n times before the next real server in the server farm is chosen.

For example, assume a server farm made up of three real servers: ServerA with n = 3, ServerB with n = 1, and ServerC with n = 2. The first three connections to the virtual server are assigned to ServerA, the fourth connection to ServerB, and the fifth and sixth connections to ServerC.

Note Assigning a weight of n = 1 to all of the servers in the server farm configures the Cisco IOS SLB device to use a simple round-robin algorithm.

GTP load balancing without GTP cause code inspection enabled requires the weighted round-robin algorithm. A server farm that uses weighted least connections can be bound to a virtual server that provides GTP load balancing without GTP cause code inspection enabled, but you cannot place that virtual server INSERVICE. If you try to do so, Cisco IOS SLB issues an error message.

Weighted Least Connections

When GTP cause code inspection is enabled, GTP load balancing supports the Cisco IOS SLB weighted least connections algorithm.

The weighted least connections algorithm specifies that the next real server chosen from a server farm for a new connection to the virtual server is the server with the fewest active connections. Each real server is assigned a weight for this algorithm, also. When weights are assigned, the server with the fewest connections is determined on the basis of the number of active connections on each server and the relative capacity of each server. The capacity of a given real server is calculated as the assigned weight of that server divided by the sum of the assigned weights of all the real servers associated with that virtual server, or n1/(n1+n2+n3...).

For example, assume a server farm made up of three real servers: ServerA with n = 3, ServerB with n = 1, and ServerC with n = 2. ServerA would have a calculated capacity of 3/(3+1+2), or half of all active connections on the virtual server, ServerB would have a calculated capacity of one-sixth of all active connections, and ServerC one-third of all active connections. At any point in time, the next connection to the virtual server would be assigned to the real server whose number of active connections is farthest below its calculated capacity.

Note Assigning a weight of n = 1 to all of the servers in the server farm configures the Cisco IOS SLB device to use a simple least-connection algorithm.

GTP load balancing without GTP cause code inspection enabled does not support the weighted least connections algorithm.

GTP load balancing with GTP cause code inspection does support the weighted least connections algorithm.

Dynamic Feedback Protocol for Cisco IOS SLB

In GTP load balancing, Cisco IOS SLB detects when a PDP context is established, but it does not detect when PDP contexts are cleared, and therefore it cannot determine the number of open PDP contexts for each GGSN. Use the Cisco IOS SLB DFP to calculate GPRS/UMTS load-balancing weights dynamically.

With Cisco IOS SLB DFP support, a DFP manager in a load-balancing environment can initiate a TCP connection with a DFP agent. Thereafter, the DFP agent collects status information from one or more real host servers, converts the information to relative weights, and reports the weights to the DFP manager. The DFP manager factors in the weights when load balancing the real servers. In addition to reporting at user-defined intervals, the DFP agent sends an early report if there is a sudden change in a real server's status.

The weights calculated by DFP override the static weights you define using the weight (server farm) command. If DFP is removed from the network, Cisco IOS SLB reverts to the static weights.

You can define Cisco IOS SLB as a DFP manager, as a DFP agent for another DFP manager (such as DistributedDirector), or as both at the same time. In such a configuration, Cisco IOS SLB sends periodic reports to DistributedDirector, which uses the information to choose the best server farm for each new connection request. Cisco IOS SLB then uses the same information to choose the best real server within the chosen server farm.

DFP also supports the use of multiple DFP agents from different client subsystems (such as Cisco IOS SLB and GPRS/UMTS) at the same time.

In GTP load balancing, you can define Cisco IOS SLB as a DFP manager and define a DFP agent on each GGSN in the server farm, and the DFP agent can report the weights of the GGSNs. The DFP agents calculate the weight of each GGSN, based on CPU utilization, processor memory, and the maximum number of PDP contexts that can be activated for each GGSN.

The weight for each GGSN is based primarily on the ratio of existing PDP contexts on the GGSN and the maximum number of allowed PDP contexts.

CPU and memory utilization become part of the weight calculation only after the utilization exceeds 85%. Because the maximum number of allowed PDP contexts is considered to be the GGSNs maximum load, you should carefully consider the value that you configure in the gprs maximum-pdp-context-allowed command, which defaults to 10,000 PDP contexts.

GTP IMSI Sticky Database Support

Cisco IOS SLB can select a GGSN, or APN if GTP APN-aware load balancing is configured, for a given International Mobile Subscriber ID (IMSI), and forward all subsequent Packet Data Protocol (PDP) create requests from the same IMSI to the selected GGSN or APN.

To enable this feature, Cisco IOS SLB uses a GTP IMSI sticky database, which maps each IMSI to its corresponding real server, in addition to its session database.

The Cisco IOS SLB creates a sticky database object when it processes the first create PDP context request for a given IMSI. The Cisco IOS SLB removes the sticky object when it receives a notification to do so from the real server, or as a result of inactivity. When the last PDP belonging to an IMSI is deleted, the GGSN notifies Cisco IOS SLB to remove the sticky object.

Sticky Database Support and GTP APN-Aware Load Balancing

The sticky IMSI feature prevents sessions from the same user for the same APN being assigned to different GGSNs. With server farm selection based on APN (APN-aware load balancing), the sticky IMSI feature ensures that a sticky entry is for the same server farm based on the APN before the IMSI can be issued. If a new create PDP context request is for a different APN, which causes GTP SLB to select a different server farm than the one for which the sticky entry was created, the server farm is respected over the real because if the real belongs to a different server farm, the serverfarm might not support the APN.

GTP APN-Aware Load Balancing

With Cisco IOS software release 12.2(18) SRB and later on the supervisor engine, GTP APN-aware load balancing can be configured.

Using the GTP APN-aware feature, a set of APNs can be mapped to a server farm in the Cisco IOS SLB. Multiple server farms can be created, each supporting a different set of APNs. Create PDP context requests are balanced across APNs.

For information on configuring GTP APN-aware load balancing, see the "Configuring GTP APN-Aware Load Balancing" section.

GTP SLB Restrictions

The following restrictions apply when configuring GTP load balancing:

•For GTP load balancing without GTP cause code inspection enabled:

–Operates in either dispatched mode or directed server NAT mode only

–Cannot load balance network-initiated PDP context requests

–Does not support the following Cisco IOS SLB functions:

- Bind IDs

- Client-assigned load balancing

- Slow Start

- Stateful backup (not supported on the Cisco 7600 platform)

- Weighted least connections load-balancing algorithm

•For GTP load balancing with GTP cause code inspection enabled:

–Operates in directed server NAT mode only

–Cannot load-balance network-initiated PDP context requests

–Requires either the SGSN or the GGSN to echo its peer

–Inbound and outbound traffic should be routed via Cisco IOS SLB

–Does not support the following Cisco IOS SLB functions:

- Bind IDs

- Client-assigned load balancing

- Slow Start

- Sticky connections

Configuring GTP Load Balancing

This section includes the following topics:

•GTP Load Balancing Configuration Task List

•Configuration Guidelines

GTP Load Balancing Configuration Task List

This section lists the tasks used to configure GTP load balancing. Detailed configuration information is contained in the referenced sections of this document or other documents. Required and optional tasks are indicated.

1. On the Cisco IOS SLB, complete the following tasks:

a. Configuring a Server Farm and Real Server (Required)

b. Configuring a Virtual Server (Required)

c. Configuring a GSN Idle Timer (Optional if GTP cause code inspection is enabled)

d. Configuring DFP Support (Optional, but recommended)

e. Configuring GTP APN-Aware Load Balancing (Optional)

2. On the GGSN, complete the following tasks:

a. Configuring a Loopback Interface for GTP SLB (Required)

b. Configuring DFP Support on the GGSN (Optional, but recommended)

c. Configuring Messaging from the GGSN to the Cisco IOS SLB (Optional)

3. Routing each GGSN to each associated serving GPRS support node (SGSN) (Required)

The route can be static or dynamic but the GGSN needs to be able to reach the SGSN. For more information, see the "Configuring a Route to the SGSN" section.

4. On the SGSN, route each SGSN to the virtual templates on each associated GGSN, and to the GGSN load-balancing virtual server (Required)

Configuration Guidelines

When configuring the network shared by Cisco IOS SLB and the GGSNs, keep the following considerations in mind:

•Specify static routes (using ip route commands) and real server IP addresses (using real commands) so that the Layer 2 information is correct and unambiguous.

•Configure the static route from the SGSN to the virtual server.

•Choose subnets carefully, using one of the following methods:

–Do not overlap virtual template address subnets.

–Specify next-hop addresses to real servers, not to interfaces on those servers.

•Cisco IOS SLB supports two types of GTP load balancing:

–GTP Load Balancing Without GTP Cause Code Inspection

–GTP Load Balancing With GTP Cause Code Inspection

•Cisco IOS SLB supports both GTP v0 and GTP v1. Support for GTP enables Cisco IOS SLB to become "GTP aware," extending Cisco IOS SLB's knowledge into Layer 5.

•On the Cisco 7600 platform, the following apply:

–Multiple GTP virtual servers are supported.

–Load balanced real servers can be internal or external to the Cisco 7600 chassis.

–Each GTP virtual server must have one unique public IP address that is reachable from the SGSNs.

–Each virtual server can correspond to one or more APNs.

–The DNS server used by the SGSNs to resolve the APNs to a GGSN IP address should use the GTP virtual IP address.

•When configuring GTP APN-aware load balancing, note the following:

–Cisco IOS software release 12.2(18) SRB and later is required on the supervisor engine and Cisco GGSN Release 7.0, Cisco IOS Release 12.4(9)XG and later is required on the GGSN.

–GTP load balancing with GTP cause code inspection enabled is not supported.

–For a given IOS SLB GTP map, you can configure up to 100 apn commands, however, because APN maps can impact performance, we recommend that you do not configure more than 10 APN maps per vserver.

–The primary and backup virtual servers should have the same mapping rules.

–The same real cannot be configured in multiple server farms.

Configuring the Cisco IOS SLB for GTP Load Balancing

To configure GTP load balancing, you must complete the following tasks on the Cisco IOS SLB:

•Configuring a Server Farm and Real Server (Required)

•Configuring a Virtual Server (Required)

•Configuring a GSN Idle Timer (Optional)

•Configuring DFP Support (Optional, but recommended)

•Configuring GTP APN-Aware Load Balancing (Optional)

•Verifying the Cisco IOS SLB Configuration (Optional)

Configuring a Server Farm and Real Server

When you configure the server farm and real server on the Cisco IOS SLB for GTP load balancing, use the following guidelines to ensure proper configuration:

•If GTP cause code inspection is not enabled, accept the default setting (the weighted round-robin algorithm) for the predictor command.

If GTP cause code inspection is enabled, you can specify either the weighted round-robin algorithm (roundrobin) or the weighted least connections (leastconns) algorithm.

•Specify the IP addresses (virtual template addresses, for Cisco GGSNs) of the real servers performing the GGSN function, using the real command.

•Specify a reassign threshold less than the SGSN's N3-REQUESTS counter value by using the reassign command.

To configure a Cisco IOS SLB server farm, use the following commands, beginning in global configuration mode:

Router-SLB(config)# ip slb serverfarm 
serverfarm-name

Router(config-slb-sfarm)#

Router-SLB(config-slb-sfarm)# predictor [roundrobin 
| leastconns]

Router-SLB(config-slb-sfarm)# nat server

Router-SLB(config-slb-sfarm)# real ip-address [port]

Router-SLB(config-slb-real)# faildetect numconns 
number-conns [numclients number-clients]

Router-SLB(config-slb-real)# maxconns number-conns

Router-SLB(config-slb-real)# reassign threshold

Router-SLB(config-slb-real)# retry retry-value

Router-SLB(config-slb-real)# weight weighting-value

Router-SLB(config-slb-real)# inservice

Configuring a Virtual Server

When you configure the virtual server on the Cisco IOS SLB for GTP load balancing, use the following guidelines to ensure proper configuration:

•Configure a static route from the SGSN to the virtual server.

•Specify a virtual GGSN IP address as the virtual server, and use the udp keyword option.

•To load-balance GTP v1 sessions, specify port number 2123, if the GGSNs and SGSNs are in compliance with the ETSI standard, or specify port number 0 or any to configure an all-port virtual server (that is, a virtual server that accepts flows destined for all ports).

•To load-balance GTP v0 sessions, specify port number 3386, if the GGSNs and SGSNs are in compliance with the European Telecommunications Standards Institute (ETSI) standard, or specify port number 0 or any to configure an all-port virtual server.

•To enable GTP load balancing without GTP cause code inspection, specify the service gtp keyword option.

•To enable GTP load balancing with GTP cause code inspection, specify the service gtp-inspect keyword option.

In GTP load balancing without GTP cause code inspection enabled, when you configure the GTP idle timer using the idle command, specify a GTP idle timer greater than the longest possible interval between PDP context requests on the SGSN.

To configure an Cisco IOS SLB virtual server, use the following commands, beginning in global configuration mode:

Router-SLB(config)# ip slb vserver 
virtual_server-name

Router-SLB(config-slb-vserver)# virtual ip-addr 
[netmask [group]] {esp | gre | protocol}

Router(config-slb-vserver)# virtual ip-addr 
[netmask [group]] {tcp | udp} [port | any] 
[service service]

Router-SLB(config-slb-vserver)# idle [gtp request] 
duration

Router-SLB(config-slb-vserver)# inservice

Router-SLB(config-slb-vserver)# client {ip-address 
network-mask [exclude] | gtp carrier-code [code]}

Router-SLB(config-slb-vserver)# replicate casa 
listen-ip remote-ip port [interval] [password [0 | 
7] password timeout]

Configuring a GSN Idle Timer

When GTP cause code inspection is enabled, you can configure the amount of time that the Cisco IOS SLB will maintain sessions to and from and idle GGSN or SGSN.

To configure a GSN idle timer, enter the following command in global configuration mode on the Cisco IOS SLB:

Router-SLB(config)# ip slb timers gtp gsn duration

Configuring DFP Support

You can define Cisco IOS SLB as a DFP manager, as a DFP agent for another DFP manager (such as DistributedDirector), or as both at the same time. Depending on your network configuration, you might enter the commands for configuring Cisco IOS SLB as a DFP manager and the commands for configuring Cisco IOS SLB as a DFP agent on the same device or on different devices.

To configure Cisco IOS SLB as a DFP manager, and to identify a DFP agent with which Cisco IOS SLB can initiate connections, use the following commands, beginning in global configuration mode:

Router-SLB(config)# ip slb dfp [password [0|7] 
password [timeout]]

Router-SLB(config-slb-dfp)# agent ip_address 
port-number [timeout [retry_count [retry_interval]]]

Configuring GTP APN-Aware Load Balancing

GTP APN-aware load balancing enables you to load balance across APNs.

When implementing GTP APN-aware load balancing, a set of APNs must be defined in a Cisco IOS SLB GTP map created on the IOS SLB. Then, the IOS SLB GTP map must be associated with a server farm under the virtual template on the IOS SLB.

To configure GTP APN-aware load balancing, complete the tasks in the following sections:

•Configuring a Cisco IOS SLB GTP Map for GTP APN-Aware Load Balancing

•Associating an IOS SLB GTP Map to a Server Farm on the Virtual Server

Prerequisites and Restrictions

When configuring GTP APN-aware load balancing, note the following:

•Cisco IOS software release 12.2(18) SRB and later is required on the supervisor engine and Cisco GGSN Release 7.0, Cisco IOS Release 12.4(9)XG and later is required on the GGSN.

•GTP load balancing with GTP cause code inspection enabled is not supported.

•For a given IOS SLB GTP map, you can configure up to 100 apn commands, however, because APN maps can impact performance, we recommend that you do not configure more than 10 APN maps per vserver.

•The primary and backup virtual servers should have the same mapping rules.

•The same real cannot be configured in multiple server farms.

Configuring a Cisco IOS SLB GTP Map for GTP APN-Aware Load Balancing

To enable APN-aware load balancing, an IOS SLB GTP map that groups certain APNs must be configured.

To configure an IOS SLB GTP map for load balancing across APNs, use the following commands, beginning in global configuration mode:

Associating an IOS SLB GTP Map to a Server Farm on the Virtual Server

After an IOS SLB GTP map has been created, it must be associated to the server farm when configuring the virtual server.

Note To change map configurations the virtual server must be taken out of service. The NAT modes on the primary and backup server farms for each map must match.

To specify a IOS SLB GTP map when associating a server farm with the virtual server, use the following command in virtual server configuration mode on the IOS SLB:

GTP APN-Aware Load Balancing Configuration Example

The following configuration example, from the IOS SLB, shows the IOS SLB GTP map configuration, and the map-to-server farm association under the virtual template.

!

/* server-farm configurations */

ip slb serverfarm farm1

 real 10.0.0.1

  inservice

 real 10.0.0.2

  inservice

ip slb serverfarm farm4

 real 10.0.0.7

  inservice

 real 10.0.0.8

  inservice

ip slb serverfarm farm5

 real 10.0.0.9

  inservice

 real 10.0.0.10

  inservice

!

/* GTP maps for GTP APN-aware SLB */

ip slb map 1 gtp

  apn www.*.edu

ip slb map 4 gtp

  apn abc.company1.com

  apn xyz.company2.com

ip slb map 5 gtp

  apn company3.com

!

/* associate the GTP map with server farm under virtual server */ 

ip slb vserver GGSN_SERVER

  virtual 10.10.10.10 udp 0 service gtp

  serverfarm farm1 map 1 priority 3

  serverfarm farm2 backup farm4 map 1 priority 2

  serverfarm farm4 map 4 priority 5

  serverfarm farm5 map 5 priority 4

  serverfarm farm6

Verifying the Cisco IOS SLB Configuration

This section describes how to verify the Cisco IOS SLB configuration. It includes the following topics:

•Verifying the Virtual Server

•Verifying the Server Farm

•Verifying Cisco IOS SLB Connectivity

Verifying the Virtual Server

The following show ip slb vserver command verifies the configuration of the virtual servers PUBLIC_HTTP and RESTRICTED_HTTP:

Router-SLB# show ip slb vserver

slb vserver      prot  virtual               state         conns

-------------------------------------------------------------------

PUBLIC_HTTP      TCP   10.0.0.1:80           OPERATIONAL     0

RESTRICTED_HTTP  TCP   10.0.0.2:80           OPERATIONAL     0

IOSSLB#

Verifying the Server Farm

The following show ip slb reals command displays the status of server farms PUBLIC and RESTRICTED, the associated real servers, and their status:

Router-SLB# show ip slb real

real                    farm name        weight   state          conns

---------------------------------------------------------------------

10.1.1.1                 PUBLIC           8       OPERATIONAL      0

10.1.1.2                 PUBLIC           8       OPERATIONAL      0

10.1.1.3                 PUBLIC           8       OPERATIONAL      0

10.1.1.20                RESTRICTED       8       OPERATIONAL      0

10.1.1.21                RESTRICTED       8       OPERATIONAL      0

IOSSLB#

The following show ip slb serverfarm command displays the configuration and status of server farms PUBLIC and RESTRICTED:

Router-SLB# show ip slb serverfarm

server farm      predictor    nat   reals   bind id

---------------------------------------------------

PUBLIC           ROUNDROBIN   none  3       0

RESTRICTED       ROUNDROBIN   none  2       0

IOSSLB#

Verifying Cisco IOS SLB Connectivity

To verify that the Cisco IOS SLB feature has been installed and is operating correctly, ping the real servers from the Cisco IOS SLB switch, and then ping the virtual servers from the clients.

The following show ip slb stats command displays detailed information about the Cisco IOS SLB 
network status:

Router-SLB# show ip slb stats

Pkts via normal switching:    0

Pkts via special switching:   0

Pkts via slb routing:         0

Pkts Dropped:                 0

Connections Created:          0

Connections Established:      0

Connections Destroyed:        0

Connections Reassigned:       0

Zombie Count:                 0

Connections Reused:           0

Connection Flowcache Purges:  0

Failed Connection Allocs:     0

Failed Real Assignments:      0

RADIUS framed-ip Sticky Count:0

RADIUS username Sticky Count: 0

See the "Monitoring and Maintaining the Cisco IOS SLB Feature" section for additional commands used to verify Cisco IOS SLB networks and connections.

Configuring the GGSN for GTP Load Balancing

To configure GTP load balancing on the GGSN, complete the tasks in the following sections:

•Configuring a Loopback Interface for GTP SLB (Required if using dispatched mode without GTP cause code inspection enabled)

•Configuring DFP Support on the GGSN (Optional, but recommended)

Configuring a Loopback Interface for GTP SLB

To enable GTP load balancing, a loopback interface must be configured with the same IP address as the virtual server on the Cisco IOS SLB on each GGSN in a farm.

To create a loopback interface, use the following commands, beginning in global configuration mode:

Router-GGSN(config)# interface loopback number

Router-GGSN(config-if)# ip address ip-address mask 

Configuring DFP Support on the GGSN

To configure DFP support for GTP SLB, you must complete the following tasks:

•Configuring the GGSN as a DFP Agent

•Configuring the Maximum DFP Weight for a GGSN

•Configuring the Maximum Number of PDP Contexts for a GGSN

Configuring the GGSN as a DFP Agent

For complete information on configuring a DFP agent, refer to the DFP Agent Subsystem feature module.

To define the port number to be used by the DFP manager (the Cisco IOS SLB in this instance) to connect to the DFP agent, enter the following commands in order, beginning in global configuration mode:

Router-GGSN(config)# ip dfp agent gprs

Router-GGSN(config-dfp)# interval seconds 

Router-GGSN(config-dfp)# password [0|7] password 
[timeout] 

Router-GGSN(config-dfp)# port port-number 

Router-GGSN(config-dfp)# inservice 

Configuring the Maximum DFP Weight for a GGSN

If you use DFP with GTP load balancing, each GGSN that acts as a DFP agent has a maximum weight that it can send to a DFP manager. For each GGSN, you can accept the default maximum weight, or you can specify a different maximum weight.

To specify the maximum weight for a GGSN, use the following command in global configuration mode on the GGSN:

Router-GGSN(config)# gprs dfp max-weight 
[max-weight-value]

Configuring the Maximum Number of PDP Contexts for a GGSN

If you use DFP with GTP load balancing, you must specify a maximum number of PDP contexts for each GGSN, using the gprs maximum-pdp-context-allowed command. Do not accept the default value of 10000 PDP contexts. Significantly lower values, including the default value of 10,000, can impact capacity in a GPRS/UMTS load-balancing environment.

Note DFP weighs PPP PDPs against IP PDPs, with one PPP PDP equal to 8 IPv4 PDPs. One IPv6 PDP counts as four IPv4 PDPs. Therefore, when using DFP, be aware that the configured maximum number of PDP contexts affects the GGSN weight. The lower the maximum number of PDP contexts, the lower the weight, when all other parameters remain the same.

To configure a maximum number of PDP contexts for a GGSN, use the following command in global configuration mode on the GGSN:

Router-GGSN(config)# gprs maximum-pdp-context-allowed 
[pdp-contexts]

Configuring Messaging from the GGSN to the Cisco IOS SLB

The GGSN-IOS SLB messaging feature enables you to configure the GGSN to notify the Cisco IOS SLB when a certain condition exists that affects a session forwarded by the Cisco IOS SLB. The notification also instructs the Cisco IOS SLB on how to react to the condition.

There are two types of GGSN-IOS SLB notifications that can be configured using the gprs slb notify command—CAC failure notifications and delete notifications (for GTP IMSI sticky database support). The following sections describe how to configure each of them:

•Configuring Support for GGSN-IOS SLB Messaging CAC Failure Notifications

•Configuring Support for GGSN-IOS SLB Messaging Delete Notifications (GTP IMSI Sticky Database Support)

Configuring Support for GGSN-IOS SLB Messaging CAC Failure Notifications

The GGSN can be configured to notify the Cisco IOS SLB when a UMTS QoS CAC failure has caused a Create PDP Context request to be rejected.

CAC failure notifications sent by the GGSN include the following information elements (IEs):

•Type—Notification type (reassign).

•Session identifier—Session key on the Cisco IOS SLB that identifies the session to which a notification belongs.

•Create response—Create response that the GGSN would send to the SGSN when a failure occurred. If there is not an alternate GGSN available to which to reassign the session, or if the maximum number of reassign attempts has been exceeded, the Cisco IOS SLB relays this information to the SGSN.

The way you configure support for CAC failure notifications depends on whether the Cisco IOS SLB is operating in dispatched mode or directed server NAT mode. For information on each procedure, see the following sections:

•Configuring CAC Failure Notification Support when the Cisco IOS SLB is in Dispatched Mode

•Configuring CAC Failure Notification Support when the Cisco IOS SLB is in Directed Server NAT Mode

Configuring CAC Failure Notification Support when the Cisco IOS SLB is in Dispatched Mode

If the Cisco IOS SLB is functioning in dispatched mode, the virtual server that forwarded the Create PDP Context request to the GGSN is known to the GGSN, and the GGSN can send CAC failure notifications directly to the server.

To configure the GGSN to send CAC failure notifications to the Cisco IOS SLB when the Cisco IOS SLB is in dispatched mode, use the following command in global configuration mode:

Router-GGSN(config)# gprs slb mode dispatched

Router-GGSN(config)# gprs slb notify cac-failure

To enable CAC failure notification support on the Cisco IOS SLB, use the following command in virtual server mode:

Router-SLB(config-slb-vserver)# gtp notification cac 
count

Configuring CAC Failure Notification Support when the Cisco IOS SLB is in Directed Server NAT Mode

If the Cisco IOS SLB is functioning in directed server NAT mode, the virtual server is not known to the GGSN. Therefore, in addition to configuring the GGSN to send CAC failure notifications to the Cisco IOS SLB, a list of virtual servers must be defined on the GGSN using the gprs slb vserver global configuration command, and the Cisco IOS SLB mode of operation must be defined using the gprs slb mode global configuration command.

Note If the Cisco IOS SLB operation mode and virtual servers are not defined on the GGSN when the Cisco IOS SLB is functioning in directed server NAT mode, support for CAC failure notification is not enabled, even if the gprs slb notify cac-failure and gtp notification cac commands are configured.

To enable the GGSN to send CAC failure notifications to the Cisco IOS SLB when the Cisco IOS SLB is in directed server NAT mode, use the following commands while in global configuration mode:

Router-GGSN(config)# gprs slb mode directed

Router-GGSN(config)# gprs slb notify cac-failure

Router-GGSN(config)# gprs slb vserver ip_address 
[next-hop ip ip-address [vrf name]]

To enable CAC failure notification support on the Cisco IOS SLB, use the following command in virtual server mode:

Router-SLB(config-slb-vserver)# gtp notification cac 
count

Configuring Support for GGSN-IOS SLB Messaging Delete Notifications (GTP IMSI Sticky Database Support)

When support for delete notifications is configured on the GGSN and the Cisco IOS SLB, a sticky database entry is created on the Cisco IOS SLB when the first Create PDP Context request from a subscriber is received. When the last PDP context of that IMSI is deleted on the GGSN, the GGSN sends a delete notification to the Cisco IOS SLB that instructs the Cisco IOS SLB to remove the sticky entry from the database.

Note This configuration requires that the virtual virtual server configuration command be configured with the service gtp keywords specified.

Note If the sticky gtp imsi command is configured under multiple vservers, the group number configuration facilitate sharing of the sticky object in the event the same MS connects through different vservers. All vservers that have the same sticky group number share the sticky IMSI entry for a user.

To configure the GGSN to send a delete notification to the Cisco IOS SLB when the last PDP context of an IMSI is deleted on the GGSN, complete the following tasks while in global configuration mode:

Router-GGSN(config)# gprs slb mode {dispatched | 
directed}

Router-GGSN(config)# gprs slb notify session-deletion

Router-GGSN(config)# gprs slb vservers ip_address 
[next-hop ip ip-address [vrf name]]

To configure GTP IMSI sticky database support on the Cisco IOS SLB, complete the following task while in virtual server configuration mode:

Router-SLB(config-slb-vserver)# sticky gtp imsi [group 
number]

Monitoring and Maintaining the Cisco IOS SLB Feature

To clear, obtain, and display GTP SLB information on the GGSN, use the following commands in privileged EXEC mode:

Router-GGSN# clear gprs slb statistics

Router-GGSN# show gprs slb detail

Router-GGSN# show gprs slb mode

Router-GGSN# show gprs slb statistics

Router-GGSN# show gprs slb vservers

To obtain and display information about the GTP SLB on the Cisco IOS SLB, use the following commands in privileged EXEC mode on the Cisco IOS SLB:

Router-SLB# show ip slb conns [vserver virtual_server-name | 
client ip-address | firewall firewallfarm-name] [detail]

Router-SLB# show ip slb dfp [agent agent_ip_address 
port-number | manager manager_ip_address | detail | weights]

Router-SLB# show ip slb gtp {gsn [gsn-ip-address] | nsapi 
[nsapi-key] [detail]

Router-SLB# show ip slb reals [sfarm server-farm] [detail]

Router-SLB# show ip slb replicate

Router-SLB# show ip slb serverfarms [name serverfarm-name] 
[detail]

Router-SLB show ip slb sessions [gtp | gtp-inspect | radius] 
[vserver virtual-server] [client ip-addr netmask] [detail]

Router=SLB# show ip slb stats

Router-SLB# show ip slb sticky gtp imsi [id imsi] 

Router-SLB# show ip slb vserver [name virtual_server] 
[redirect] [detail]

Configuration Examples

This section provides an example of the GGSN Cisco IOS SLB examples. For complete descriptions of the GGSN commands in this section, refer to the Cisco GGSN Release Command Reference. For complete descriptions of the Cisco IOS SLB commands in this section, refer to the IOS Server Load Balancing feature module documentation.

This section includes examples of Cisco IOS SLB with GTP load balancing and NAT configured on the Cisco 7600 platform:

•Cisco IOS SLB Configuration Example

•GGSN1 Configuration Example

Cisco IOS SLB Configuration Example

hostname 7600-a

!

ip slb probe PINGPROBE ping

 interval 3

 faildetect 3

!

ip slb serverfarm SAMI1

 nat server

 probe PINGPROBE

!

 real 9.9.9.72

  reassign 4

  faildetect numconns 255 numclients 8

  inservice

!

 real 9.9.9.73

  reassign 4

  faildetect numconns 255 numclients 8

  inservice

!

 real 9.9.9.74

  reassign 4

  faildetect numconns 255 numclients 8

  inservice

!

 real 9.9.9.75

  reassign 4

  faildetect numconns 255 numclients 8

  inservice

!

 real 9.9.9.76

  reassign 4

  faildetect numconns 255 numclients 8

  inservice

!

ip slb vserver V0-GGSN

 virtual 10.10.10.10 udp 3386 service gtp

 serverfarm SAMI1

 idle gtp request 100

 inservice

!

ip slb vserver V1-GGSN

 virtual 10.10.10.10 udp 2123 service gtp

 serverfarm SAMI1

 idle gtp request 100

 inservice

!

ip slb dfp password ciscodfp 0

 agent 9.9.9.72 1111 30 0 10

 agent 9.9.9.73 1111 30 0 10

 agent 9.9.9.74 1111 30 0 10

 agent 9.9.9.75 1111 30 0 10

 agent 9.9.9.76 1111 30 0 10

!

interface FastEthernet9/36

 description TO SGSN

 no ip address

 switchport

 switchport access vlan 302

!

interface Vlan101

 description Vlan to GGSN for GN

 ip address 10.1.1.1 255.255.255.0

!

interface Vlan302

 ip address 40.0.2.1 255.255.255.0

!

router ospf 300

 log-adjacency-changes

 summary-address 9.9.9.0 255.255.255.0

 redistribute static subnets route-map GGSN-routes

 network 40.0.2.0 0.0.0.255 area 300

 network 40.0.3.0 0.0.0.255 area 300

!

ip route 9.9.9.72 255.255.255.255 10.1.1.72

ip route 9.9.9.73 255.255.255.255 10.1.1.73

ip route 9.9.9.74 255.255.255.255 10.1.1.74

ip route 9.9.9.75 255.255.255.255 10.1.1.75

ip route 9.9.9.76 255.255.255.255 10.1.1.76

!

access-list 1 permit 9.9.9.0 0.0.0.255

!

route-map GGSN-routes permit 10

 match ip address 1

!

!

GGSN1 Configuration Example

!

ip dfp agent gprs

 port 1111

 password ciscodfp 0

 inservice

!

interface Loopback100

 description GPRS GTP V-TEMPLATE IP ADDRESS

 ip address 9.9.9.72 255.255.255.0

!

interface GigabitEthernet0/0.2

 description Gn Interface

 encapsulation dot1Q 101

 ip address 10.1.1.72 255.255.255.0

 no cdp enable

!

interface Virtual-Template1

 description GTP v-access

 ip unnumbered Loopback100

 encapsulation gtp

 gprs access-point-list gprs

!

! route to SGSNs

ip route 40.1.2.1 255.255.255.255 10.1.1.1

ip route 40.2.2.1 255.255.255.255 10.1.1.1