CCSP Self-Study: Securing Cisco IOS Networks (SECUR)

Filtering Router Service Traffic

This section explains how to implement ACLs to filter IP traffic that is destined for the following router services:

• Telnet

• SNMP

• Routing protocols

Telnet Service

Telnet (vty) is typically used by systems administrators to access the router for config-uration and maintenance. Figure 4-28 shows a portion of the theoretical network from Figure 4-27.

Figure 4-28. Telnet Service Filtering

You should restrict which hosts have access to the vty lines of the router by using an ACL, as demonstrated in Example 4-16.

Example 4-16. Filtering Telnet Service

R2(config)# access-list 105 permit host 16.2.1.3 eq 23 any log R2(config)# ...