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Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

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Denying and Permitting Access to a Terminal Line

Dell EMC 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 method is a generic way of configuring access restrictions.
  • To be able to filter access exclusively using either IPv4 or IPv6 rules, 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
access-class access-list-name [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.

DellEMC(config-std-nacl)#show config
!
ip access-list standard myvtyacl
  seq 5 permit host 10.11.0.1
DellEMC(config-std-nacl)#line vty 0
DellEMC(config-line-vty)#show config
line vty 0
  access-class myvtyacl
DellEMC(conf-ipv6-acl)#do show run acl
!
ip access-list extended testdeny
seq 10 deny ip 30.1.1.0/24 any
seq 15 permit ip any any
!
ip access-list extended testpermit
seq 15 permit ip any any
!
ipv6 access-list testv6deny
seq 10 deny ipv6 3001::/64 any
seq 15 permit ipv6 any any
!
DellEMC(conf)#
DellEMC(conf)#line vty 0 0
DellEMC(config-line-vty)#access-class testv6deny ipv6
DellEMC(config-line-vty)#access-class testvpermit ipv4
DellEMC(config-line-vty)#show c
line vty 0
exec-timeout 0 0
access-class testpermit ipv4
access-class testv6deny ipv6
!

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