Enterasys Networks 9034385 - Manual (Page 85)

Out-of-Band NAC Design Procedures
Enterasys NAC Design Guide 5-21
Figure 5-5 NAC Gateway Redundancy
It is important that the secondary NAC Gateway does not exceed maximum capacity if the
primary NAC Gateway fails on the network. For example, let’s say that two NAC Gateways,
both running at maximum load on the network, are being used by six switches. NAC Gateway
#1 is the primary gateway for switch A, switch B, and switch C, and NAC Gateway #2 is the
primary gateway for switch D, switch E, and switch F. In this scenario, NAC Gateway #1
should not be configured to serve as secondary for NAC Gateway #2 and vice versa. This is
because if NAC Gateway #1 fails, NAC Gateway #2, which is already running at maximum
capacity before NAC Gateway #1ʹs failure, will not be able to handle the end‐systems failing
over from NAC Gateway #1. To avoid exceeding these limits, extra NAC Gateway appliances
must be deployed on the network to serve as secondary NAC Gateways for these six switches.
To summarize, NAC Gateway redundancy may be accomplished using two different approaches:
• Active‐standby redundancy
In this redundancy approach, a set of switches are configured to use the same primary NAC
Gateway (assuming these switches observe the NAC Gatewayʹs capacity limitations
previously described) and use the same secondary NAC Gateway as a backup (assuming the
secondary NAC Gateway is the same model as the primary). The secondary NAC Gateway is
not configured as a primary NAC Gateway for any switch on the network and therefore is
inactive until a primary NAC Gateway fails. For example, if switch A, switch B, and switch C
use NAC Gateway #1 as a primary gateway, then all three switches can be configured to use
NAC Gateway #2 on the network as the backup. In this configuration, if switch A, switch B, or
switch C loses connectivity to NAC Gateway #1, the switch would seamlessly transition to
using NAC Gateway #2. In the worst‐case scenario where all three switches lose connectivity
to NAC Gateway #1, NAC Gateway #2 would be able to handle all authentication requests
from these three switches. In this redundancy configuration, NAC Gateway #2 is completely
idle on the network and only utilized if one of the switches cannot communicate to NAC
Gateway #1.
• Active‐active redundancy
In this redundancy approach, the primary NAC Gateway for one switch is a secondary NAC
Gateway for another switch. For this configuration, the same primary NAC Gateway is
utilized for a group of switches, with this NAC Gateway running at only half the maximum
load. Another group of switches utilizes a different primary NAC Gateway (assuming it is the
same model) also running half the maximum load. Then, each group of switches can use the
other NAC Gateway as the secondary gateway. This redundancy configuration guarantees
that in the worst‐case scenario, when all switches in one group lose communication to their