Cisco Cisco IOS Software Release 12.2(18)SXE

IOS SLB supports the Exchange Director for the Cisco Mobile Exchange (CMX) for Catalyst 6500 
family switches and Cisco 7600 series routers. The Exchange Director provides the following features:

General packet radio service (GPRS) is the packet network infrastructure based on the European 
Telecommunications Standards Institute (ETSI) Global System for Mobile Communication (GSM) phase 2+ 
standards for transferring packet data from the GSM mobile user to the packet data network (PDN). The 
Cisco gateway GPRS support node (GGSN) interfaces with the serving GPRS support node (SGSN) 
using the GPRS Tunneling Protocol (GTP), which in turn uses UDP for transport. IOS SLB provides 
GPRS load balancing and increased reliability and availability for the GGSN.

When configuring the network shared by 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) 
such that the Layer 2 information is correct and unambiguous.

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.

IOS SLB assigns all PDP context creates from a specific IMSI to the same GGSN.

IOS SLB supports both GTP Version 0 (GTP v0) and GTP Version 1 (GTP v1). Support for GTP 
enables IOS SLB to become “GTP aware,” extending IOS SLB’s knowledge into Layer 5.

IOS SLB supports two types of GPRS load balancing:

GPRS 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 NAT mode, but not in directed client NAT 
mode. In dispatched mode, the GGSNs must be Layer 2-adjacent to the IOS SLB device.

Does not support stateful backup. See the 

 for more 

information.