Telnet

Telnet provides unencrypted remote terminal access on IOS-XR. Because traffic is sent in cleartext, telnet should only be enabled in isolated management networks or legacy environments where SSH is not supported. Per-VRF server limits and ACLs control which VRFs accept inbound sessions and how many concurrent connections are allowed. DSCP marking can be applied per VRF for QoS classification, and client source interfaces determine the originating address for outbound telnet connections.

Diagram

Classes

iosxr

Name	Type	Constraint	Mandatory	Default Value
devices	List	devices	No
device_groups	List	device_groups	No
global	Class	global	No

devices (iosxr)

Name	Type	Constraint	Mandatory	Default Value
configuration	Class	configuration	No

device_groups (iosxr)

Name	Type	Constraint	Mandatory	Default Value
configuration	Class	configuration	No

global (iosxr)

Name	Type	Constraint	Mandatory	Default Value
configuration	Class	configuration	No

configuration (iosxr.devices)

Name	Type	Constraint	Mandatory	Default Value
telnet	Class	telnet	No

telnet (iosxr.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
source_interface_ipv4	String		No
source_interface_ipv6	String		No
vrfs	List	vrfs	No

vrfs (iosxr.devices.configuration.telnet)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
ipv4_access_list	String		No
ipv4_dscp	Integer	min: 0, max: 63	No
ipv4_max_servers	Integer	min: 1, max: 100	No
ipv6_access_list	String		No
ipv6_max_servers	Integer	min: 1, max: 100	No

Example YAML Code:

Example-1: Set the source address for outbound telnet connections to a management interface.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        telnet:
          source_interface_ipv4: GigabitEthernet0/0/0/1
          source_interface_ipv6: GigabitEthernet0/0/0/1

Example-2: Limit inbound telnet sessions per VRF with ACL filtering.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        telnet:
          source_interface_ipv4: GigabitEthernet0/0/0/1
          vrfs:
            - name: VRF1
              ipv4_max_servers: 4
              ipv4_access_list: ACCESS1
              ipv6_max_servers: 4
              ipv6_access_list: ACCESS11
            - name: MGMT
              ipv4_max_servers: 10
              ipv6_max_servers: 10

Example-3: Apply DSCP marking to telnet traffic in specific VRFs for QoS classification.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        telnet:
          vrfs:
            - name: TOI
              ipv4_dscp: 55
            - name: PROD
              ipv4_dscp: 46