Specifications

Configuring Resource Pool Management
Configuration Examples for RPM
DC-756
Cisco IOS Dial Technologies Configuration Guide
VPDN Load Sharing and Backing Up Between Multiple HGW/LNSs Example
Cisco IOS software enables you to balance and back up VPDN sessions across multiple tunnel endpoints
(HGW/LNS). When a user or session comes into the NAS/LAC, a VPDN load-balancing algorithm is
triggered and applied to the call. The call is then passed to an available HGW/LNS. You can modify this
function by limiting the number of sessions supported on an HGW/LNS router and limiting the number
of MLP bundles and links.
Figure 109 shows an example of one NAS/LAC that directs calls to two HGW/LNS routers by using the
L2TP tunneling protocol. Each router has a different number of supported sessions and works at a
different speed. The NAS/LAC is counting the number of active simultaneous sessions sent to each
HGW/LNS.
Figure 109 Home Gateway Load Sharing and Backup
In a standalone NAS environment (no RPMS server used), the NAS has complete knowledge of the status
of tunnel endpoints. Balancing across endpoints is done by a “least-filled tunnel” or a “next-available
round robin” approach. In an RPMS-controlled environment, RPMS has the complete knowledge of
tunnel endpoints. However, the NAS still has the control over those tunnel endpoints selected by RPMS.
A standalone NAS uses the following default search criteria for load-balancing traffic across multiple
endpoints (HGW/LNS):
• Select any idle endpoint—an HGW/LNS with no active sessions.
• Select an active endpoint that currently has a tunnel established with the NAS.
• If all specified load-sharing routers are busy, select the backup HGW. If all endpoints are busy,
report that the NAS cannot find an IP address to establish the call.
Note This default search order criteria is independent of the Cisco RPMS application scenario. A
standalone NAS uses a different load-sharing algorithm than the Cisco RPMS. This search criteria
will change as future enhancements become available.
AS5000 series
NAS
POTS
line
BRI
line
PSTN
L2TP
tunnel
L2TP
tunnel
PRI
16747
Modem
Cisco 776
Cisco 7246
home gateway
200 sessions
Cisco 3640
home gateway
50 sessions
PC
IP
network