Cisco Router Security Best Practices
CERT-In Security Guidelines (CISG-2004-02) Issued by CERT-In (Indian Computer Emergency Response Team), Ministry of Communications & IT, Govt. of India
Introduction
Routers are the first line of defense in most enterprise networks. Securing them properly is critical to protect data, prevent misuse, and keep business operations safe. These guidelines outline practical steps to harden a Cisco router.
(Note: Advanced routing protocols like BGP, OSPF, RIP, and VRRP are outside the scope. Always run the latest Cisco IOS version.)
1. Access Management
Think of access management as controlling “who gets the keys to the router.”
Console Access: Always enforce local logins, set session timeouts, and create at least one local user with a strong password.
Auxiliary Port: If not needed, lock it down. Use exec-timeout and no exec to prevent unauthorized use.
VTY (Telnet) Access: Disable Telnet by default. If remote access is required, allow only trusted IPs. Use TCP keepalives and disable unused VTY lines.
Enable Secret: Protect privileged mode with a strong secret password.
2. Disable Unnecessary Services
Every unused service is a potential doorway for attackers. Shut down what you don’t need:
Finger, Identd, HTTP server
Small TCP/UDP servers
Bootp, CDP, TFTP
Remote config loading, boot network, DNS lookup
3. SNMP Security
If you don’t use SNMP, disable it completely.
If you do, protect it with ACLs and strong, non-default community strings.
4. Routing Rules
Reduce the risk of spoofing and malicious probes:
Disable directed broadcasts, proxy ARP, mask replies, redirects, and source routing.
Use TCP keepalives to kill dead sessions.
Enable Unicast Reverse Path Forwarding (uRPF) to drop spoofed packets.
5. Access Control Lists (ACLs)
ACLs are your network’s “traffic cops.” Use them wisely:
Block private and reserved IP ranges.
Apply ingress filtering to stop spoofed packets.
Only allow essential services (like web, mail, DNS) from trusted IPs.
Allow return traffic (ACK packets, DNS replies, FTP data) selectively.
Permit only safe ICMP types (ping replies, unreachable messages, etc.).
Deny everything else by default.
Apply ACLs both inbound and outbound for maximum protection.
6. Logging
Always know what’s happening on your router:
Enable logging.
Send logs and alerts to a trusted syslog server for monitoring.
7. Benchmark
Don’t just configure—verify. Use security benchmarks (like CIS Router Benchmarks) to test if your setup holds up against best practices.
8. References
Conclusion
Securing a Cisco router is not a one-time task but an ongoing process. By controlling access, disabling unnecessary services, applying strict ACLs, and monitoring logs, organizations can significantly reduce their exposure to cyber threats. Following these best practices ensures that routers remain a strong, reliable barrier between the internal network and potential attackers. Regular benchmarking and updates help maintain a secure, resilient infrastructure.