The following sections discuss the key areas of the small enterprise network security design.
Network Foundation Protection
Small enterprise networks are built with routers, switches, and other network devices that keep the applications and services running. Therefore, properly securing these network devices is critical for continued operation.
The network infrastructure of a small enterprise can be protected by implementing the Cisco SAFE best practices for the following areas:
•Infrastructure device access
–Restrict management device access to authorized parties and for the authorized ports and protocols.
–Enforce Authentication, Authorization, and Accounting (AAA) with Terminal Access Controller Access Control System (TACACS+) or Remote Authentication Dial-In User Service (RADIUS) to authenticate access, authorize actions, and log all administrative access.
–Display legal notification banners.
–Ensure confidentiality by using secure protocols like Secure Shell (SSH) and HTTPS.
–Enforce idle and session time-outs and disable unused access lines.
•Routing infrastructure
–Restrict routing protocol membership by enabling Message-Digest 5 (MD5) neighbor authentication and disabling default interface membership.
–Enforce route filters to ensure that only legitimate networks are advertised and networks that are not supposed to be propagated are never advertised.
–Log status changes of neighbor sessions to identify connectivity problems and DoS attempts on routers.
•Device resiliency and survivability
–Disable unnecessary services and implement control plane policing (CoPP).
–Enable traffic storm control.
–Implement topological, system, and module redundancy for the resiliency and survivability of routers and switches and to ensure network availability.
–Keep local device statistics.
•Network telemetry
–Enable Network Time Protocol (NTP) time synchronization.
–Collect system status and event information with Simple Network Management Protocol (SNMP), Syslog, and TACACS+/RADIUS accounting.
–Monitor CPU and memory usage on critical systems.
–Enable NetFlow to monitor traffic patterns and flows.
•Network policy enforcement
–Implement access edge filtering.
–Enforce IP spoofing protection with access control lists (ACLs), Unicast Reverse Path Forwarding (uRPF), and IP Source Guard.
•Switching infrastructure
–Implement a hierarchical design, segmenting the LAN into multiple IP subnets or virtual LANs (VLANs) to reduce the size of broadcast domains.
–Protect the Spanning Tree Protocol (STP) domain with BPDU Guard and STP Root Guard.
–Use per-VLAN Spanning Tree to reduce the scope of possible damage.
–Disable VLAN dynamic trunk negotiation on user ports.
–Disable unused ports and put them into an unused VLAN.
–Implement Catalyst Infrastructure Security Features (CISF) including port security, dynamic ARP inspection, and DHCP snooping.
–Use a dedicated VLAN ID for all trunk ports.
–Explicitly configure trunking on infrastructure ports.
–Use all tagged mode for the native VLAN on trunks and drop untagged frames.
•Network management
–Ensure the secure management of all devices and hosts within the enterprise network.
–Authenticate, authorize, and keep record of all administrative access.
–If possible, implement a separate out-of-band (OOB) management network (hardware or VLAN based) to manage systems at the main site.
–Secure the OOB by enforcing access controls, using dedicated management interfaces or virtual routing and forwarding (VRF) tables.
–Provide secure in-band management access for systems residing at the remote sites by deploying firewalls and ACLs to enforce access controls, using Network Address Translation (NAT) to hide management addresses and using secure protocols like SSH and HTTPS.
–Ensure time synchronization by using NTP.
–Secure servers and other endpoint with endpoint protection software and operating system (OS) hardening best practices.
For more detailed information on the NFP best practices, refer to "Chapter 2, Network Foundation Protection" of the Cisco SAFE Reference Guide at: http://www.cisco.com/en/US/docs/solutions/Enterprise/Security/SAFE_RG/chap2.html.
Internet Perimeter Protection
The small enterprise network design assumes the existence of a centralized Internet connection at the headquarters or main site serving users at all locations. Common services include E-mail and Web browsing for employees, the hosting of a company's website accessible to clients and partners over the Internet, and secure remote access for mobile users and remote workers. Other services may also be provided using the same infrastructure.