Enterasys Networks 9034385 - Manual (Page 94)

Inline NAC Design Procedures
5-30 Design Procedures
2. Determine the Number of NAC Controllers
The number of NAC Controllers to be deployed on the network is a function of the following
parameters:
• The network topology.
Because the NAC Controller is placed inline with traffic sourced from connecting end‐
systems, the number of NAC Controllers required is directly dependent on the network
topology. After the location of the NAC Controller is identified from the network topology, the
minimum number of NAC Controllers can be determined.
• The number of Security Domains configured on the network.
Each NAC Controller can be associated to only one Security Domain. Therefore, the number
of NAC Controllers deployed on the network will be greater than or equal to the number of
Security Domains configured in NAC Manager. To support redundancy per Security Domain,
at least two NAC Controllers must be deployed per Security Domain, as discussed below.
• The number of users and devices that are connected to each Security Domain.
Each NAC Controller appliance has the capability of supporting up to 2000 end‐systems
connected downstream as shown in the following table.
To identify the minimum number of NAC Controllers required to support inline NAC, use the
following formula:
Number of connecting end‐systems in a Security Domain / Concurrent end‐systems
supported by controller type = the number of required NAC Controllers of that type, per
Security Domain.
• The configuration of NAC Controller redundancy.
To achieve redundancy at each location in the network where the NAC Controller is
positioned, an additional NAC Controller is required, essentially doubling the total number of
required NAC Controllers. Redundancy implementation differs between Layer 2 and Layer 3
Controllers.
For a Layer 2 NAC Controller, redundancy is achieved in two different ways. Redundancy for
the NAC Policy Enforcement Point (PEP) component of the NAC Controller is achieved by
implementing 802.1w/s spanning tree between the redundant NAC Controllers as shown in
Figure 5‐9 on page 5‐31. Redundant Layer 2 NAC Controllers are active‐passive when only
one spanning tree for one VLAN is configured between the NAC Controllers, and are active‐
active when multiple spanning trees for multiple VLANs are configured between the
redundant NAC Controllers. If NAC Controller #1ʹs Policy Enforcement Point (PEP) stops
forwarding traffic, the network will automatically converge via 802.1w/s spanning tree to
forward traffic through NAC Controller #2.
Redundancy for the NAC Engine component of the NAC Controller is achieved by the
redundant NAC Controllers using each other as backup RADIUS servers. If NAC Controller
#1ʹs Engine stops processing RADIUS authentication requests, the redundant NAC Engine
will take over processing RADIUS messages as shown in
Figure 5‐9 on page 5‐31.
Table 5-5 End-System Limits for NAC Controllers
NAC Controller Model Concurrent End-Systems Supported
7S4280-19-SYS Up to 2000
2S4082-25-SYS Up to 2000