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Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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Denying and Permitting Access to a Terminal Line

Dell Networking recommends applying only standard access control lists (ACLs) to deny and permit access to VTY lines.

  • Layer 3 ACLs deny all traffic that is not explicitly permitted, but in the case of VTY lines, an ACL with no rules does not deny traffic.
  • You cannot use the show ip accounting access-list command to display the contents of an ACL that is applied only to a VTY line.
  • When you use the access-class access-list-name command without specifying the ipv4 or ipv6 attribute, both IPv4 as well as IPv6 rules that are defined in that ACL are applied to the terminal. This is a generic way of configuring access restrictions.
  • To be able to filter access exclusively using either IPv4 or IPv6 rules, you must use either the ipv4 or ipv6 attribute along with the access-class access-list-name command. Depending on the attribute that you specify ( ipv4 or ipv6), the ACL processes either IPv4 or IPv6 rules, but not both. Using this configuration, you can set up two different types of access classes with each class processing either IPv4 or IPv6 rules separately.
To apply an IP ACL to a line, Use the following command.
Apply an ACL to a VTY line. LINE mode ip access-class access-list [ipv4 | ipv6]
  • NOTE: If you already have configured generic IP ACL on a terminal line, then you cannot further apply IPv4 or IPv6 specific filtering on top of this configuration. Similarly, if you have configured either IPv4 or IPv6 specific filtering on a terminal line, you cannot apply generic IP ACL on top of this configuration. Before applying any of these configurations, you must first undo the existing configuration using the no access-class access-list-name [ipv4 | ipv6] command.

Example of an ACL that Permits Terminal Access

To view the configuration, use the show config command in LINE mode. 

Dell(config-std-nacl)#show config
                                 !
                                 ip access-list standard myvtyacl
                                 seq 5 permit host 10.11.0.1
                                 Dell(config-std-nacl)#line vty 0
                                 Dell(config-line-vty)#show config
                                 line vty 0
                                 access-class myvtyacl

Dell OS Behavior: Prior to Dell OS version 7.4.2.0, in order to deny access on a VTY line, apply an ACL and accounting, authentication, and authorization (AAA) to the line. Then users are denied access only after they enter a username and password. Beginning in Dell OS version 7.4.2.0, only an ACL is required, and users are denied access before they are prompted for a username and password.

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