Loopback

Loopback interfaces are virtual logical interfaces on NX-OS that provide a stable, always-up reference point for network services including routing protocol router IDs, management access, and service endpoints that remain accessible regardless of physical interface states. They support full Layer 3 functionality including IPv4 and IPv6 addressing with secondary addresses, VRF membership, link logging, and routing protocol participation through OSPF, OSPFv3, PIM, and IS-IS sub-sections. Loopback interfaces also support DHCP relay, IPv6 neighbor discovery configuration, access group filtering, and are essential for VXLAN VTEP source interfaces, BGP peering, and overlay network anchor points.

Diagram

Classes

interfaces (nxos.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
loopbacks	List	`[loopbacks]`	No

loopbacks (nxos.devices.configuration.interfaces)

Name	Type	Constraint	Mandatory	Default Value
id	Integer	min: `0`	Yes
interface_groups	List	String	No
shutdown	Boolean	`true`, `false`	No	`false`
description	String		No
logging_event_port_link_status	Boolean	`true`, `false`	No
vrf	String		No
ip_address	IP		No
ip_secondary_addresses	List	IP	No
ip_redirects	Boolean	`true`, `false`	No
ip_unreachables	Boolean	`true`, `false`	No
ip_port_unreachable	Boolean	`true`, `false`	No
ospf	Class	`[ospf]`	No
ospfv3	Class	`[ospfv3]`	No
pim	Class	`[pim]`	No
isis	Class	`[isis]`	No
ipv6_address_autoconfig	Boolean	`true`, `false`	No
ipv6_nd_default_route	Boolean	`true`, `false`	No
ipv6_forward	Boolean	`true`, `false`	No
ipv6_link_local_use_bia	Boolean	`true`, `false`	No
ipv6_address_use_link_local_only	Boolean	`true`, `false`	No
ipv6_verify_unicast_source_reachable_via	Choice	`disabled`, `strict`, `loose`, `loose-allow-default`, `strict-allow-vni-hosts`	No
ipv6_address_link_local	String		No
ipv6_addresses	List	`[ipv6_addresses]`	No
ip_dhcp_relay	Class	`[ip_dhcp_relay]`	No
ipv6_dhcp_smart_relay	Boolean	`true`, `false`	No
ipv6_dhcp_relay_addresses	List	`[ipv6_dhcp_relay_addresses]`	No
nd	Class	`[nd]`	No
ip_access_group_in	String		No
ip_access_group_out	String		No

ospf (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory	Default Value
process	String		Yes
advertise_secondaries	Boolean	`true`, `false`	No	`true`
advertise_subnet	Boolean	`true`, `false`	No
area	String		No
bfd	Boolean	`true`, `false`	No
cost	Integer	min: `0`, max: `65535`	No
dead_interval	Integer	min: `0`, max: `65535`	No
hello_interval	Integer	min: `0`, max: `65535`	No
mtu_ignore	Boolean	`true`, `false`	No
network	Choice	`unspecified`, `p2p`, `bcast`	No
prefix_attribute_n_flag	Choice	`unspecified`, `clear`	No
passive_interface	Boolean	`true`, `false`	No
priority	Integer	min: `0`, max: `255`	No
retransmit_interval	Integer	min: `1`, max: `65535`	No
transmit_delay	Integer	min: `1`, max: `450`	No
authentication_key	String		No
message_digest_key_id	Integer	min: `0`, max: `255`	No
authentication_key_secure_mode	Boolean	`true`, `false`	No
authentication_key_chain	String		No
message_digest_key	String		No
message_digest_key_secure_mode	Boolean	`true`, `false`	No
authentication	Choice	`unspecified`, `simple`, `md5`, `none`	No

ospfv3 (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
process	String		Yes
advertise_secondaries	Boolean	`true`, `false`	No
area	String		No
bfd	Boolean	`true`, `false`	No
cost	Integer	min: `0`, max: `65535`	No
dead_interval	Integer	min: `0`, max: `65535`	No
hello_interval	Integer	min: `1`, max: `65535`	No
network	Choice	`none`, `p2p`, `bcast`	No
passive_interface	Boolean	`true`, `false`	No
priority	Integer	min: `0`, max: `255`	No
instance_id	Integer	min: `0`, max: `255`	No
mtu_ignore	Boolean	`true`, `false`	No
retransmit_interval	Integer	min: `1`, max: `65535`	No
transmit_delay	Integer	min: `1`, max: `450`	No

pim (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
bfd_instance	Boolean	`true`, `false`	No
dr_priority	Integer	min: `1`, max: `4294967295`	No
passive	Boolean	`true`, `false`	No
sparse_mode	Boolean	`true`, `false`	No
border	Boolean	`true`, `false`	No
dr_delay	Integer	min: `1`, max: `65535`	No
jp_policy	String		No
neighbor_policy_route_map	String		No
neighbor_policy_prefix_list	String		No
strict_rfc_compliant	Boolean	`true`, `false`	No

isis (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
instance_name	String		Yes
circuit_type	Choice	`l1`, `l2`, `l12`	No
ipv4	Boolean	`true`, `false`	No
ipv6	Boolean	`true`, `false`	No
network_point_to_point	Choice	`off`, `on`, `use-all-is-mac`	No
passive_interface	Choice	`l1`, `l2`, `l12`, `no-l1`, `no-l2`, `no-l12`, `inherit-def`	No
metric_level_1	Integer	min: `0`, max: `16777216`	No
metric_level_2	Integer	min: `0`, max: `16777216`	No
ipv6_metric_level_1	Integer	min: `0`, max: `16777216`	No
ipv6_metric_level_2	Integer	min: `0`, max: `16777216`	No
priority_level_1	Integer	min: `0`, max: `127`	No
priority_level_2	Integer	min: `0`, max: `127`	No
hello_interval	Integer	min: `1`, max: `65535`	No
hello_interval_level_1	Integer	min: `1`, max: `65535`	No
hello_interval_level_2	Integer	min: `1`, max: `65535`	No
hello_multiplier	Integer	min: `3`, max: `1000`	No
hello_multiplier_level_1	Integer	min: `3`, max: `1000`	No
hello_multiplier_level_2	Integer	min: `3`, max: `1000`	No
hello_padding	Choice	`always`, `transient`, `never`	No
authentication_check	Boolean	`true`, `false`	No
authentication_check_level_1	Boolean	`true`, `false`	No
authentication_check_level_2	Boolean	`true`, `false`	No
authentication_key_chain	String		No
authentication_key_chain_level_1	String		No
authentication_key_chain_level_2	String		No
authentication_type	Choice	`clear`, `md5`, `unknown`	No
authentication_type_level_1	Choice	`clear`, `md5`, `unknown`	No
authentication_type_level_2	Choice	`clear`, `md5`, `unknown`	No
mtu_check	Boolean	`true`, `false`	No
mtu_check_level_1	Boolean	`true`, `false`	No
mtu_check_level_2	Boolean	`true`, `false`	No
bfd	Boolean	`true`, `false`	No
ipv6_bfd	Boolean	`true`, `false`	No
csnp_interval_level_1	Integer	min: `1`, max: `65535`	No
csnp_interval_level_2	Integer	min: `1`, max: `65535`	No
lsp_interval	Integer	min: `10`, max: `65535`	No
retransmit_interval	Integer	min: `1`, max: `65535`	No
retransmit_throttle_interval	Integer	min: `20`, max: `65535`	No
mesh_group	Integer	min: `0`, max: `4294967295`	No
mesh_group_blocked	Boolean	`true`, `false`	No
n_flag_clear	Boolean	`true`, `false`	No
suppress_prefix	Boolean	`true`, `false`	No

ipv6_addresses (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
address	String		Yes
type	Choice	`primary`, `secondary`	No
tag	Integer	min: `0`, max: `4294967295`	No
eui64	Boolean	`true`, `false`	No
route_preference	Integer	min: `0`, max: `255`	No

ip_dhcp_relay (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
information_trusted	Boolean	`true`, `false`	No
smart_relay	Boolean	`true`, `false`	No
subnet_broadcast	Boolean	`true`, `false`	No
information_option	Boolean	`true`, `false`	No
source_subnet	String		No
addresses	List	`[addresses]`	No

ipv6_dhcp_relay_addresses (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory	Default Value
address	String		Yes
vrf	String		No

nd (nxos.devices.configuration.interfaces.loopbacks)

Name	Type	Constraint	Mandatory
ra_boot_file_url	String		No
suppress_ra	Boolean	`true`, `false`	No
suppress_ra_mtu	Boolean	`true`, `false`	No
managed_config_flag	Boolean	`true`, `false`	No
other_config_flag	Boolean	`true`, `false`	No
redirects	Boolean	`true`, `false`	No
dad_attempts	Integer	min: `0`, max: `15`	No
dad_ns_interval	Integer	min: `1000`, max: `6000`	No
delete_adjacency_on_mac_delete	Boolean	`true`, `false`	No
dns_search_list_suppress	Boolean	`true`, `false`	No
dns_suppress	Boolean	`true`, `false`	No
hop_limit	Integer	min: `0`, max: `255`	No
mac_extract	Choice	`none`, `nud-phase`, `exclude-nud-phase`	No
mtu	Integer	min: `1280`, max: `65535`	No
ns_interval	Integer	min: `1000`, max: `3600000`	No
ra_interval	Integer	min: `4`, max: `1800`	No
ra_interval_minimum	Integer	min: `3`, max: `1350`	No
ra_lifetime	Integer	min: `0`, max: `9000`	No
reachable_time	Integer	min: `0`, max: `3600000`	No
retrans_timer	Integer	min: `0`, max: `4294967295`	No
suppress_ra_route	Boolean	`true`, `false`	No
router_preference	Choice	`unspecified`, `low`, `medium`, `high`	No

addresses (nxos.devices.configuration.interfaces.loopbacks.ip_dhcp_relay)

Name	Type	Constraint	Mandatory	Default Value
address	String		Yes
vrf	String		No

Examples

Example 1: Router-ID loopback with OSPF and PIM using an interface group

nxos:
  devices:
    - name: LEAF1
      configuration:
        interfaces:
          loopbacks:
            - id: 0
              description: Router-ID
              ip_address: 10.1.100.3/32
              interface_groups: [LOOPBACK_INTERFACE]

Example 2: VTEP source loopback and anycast RP loopback for a VXLAN fabric

nxos:
  devices:
    - name: LEAF1
      configuration:
        interfaces:
          loopbacks:
            - id: 0
              description: Router-ID
              ip_address: 10.1.100.3/32
              interface_groups: [LOOPBACK_INTERFACE]
            - id: 1
              description: VTEP-Source
              ip_address: 10.1.200.1/32
              interface_groups: [LOOPBACK_INTERFACE]

    - name: SPINE1
      configuration:
        interfaces:
          loopbacks:
            - id: 0
              description: Router-ID
              ip_address: 10.1.100.1/32
              interface_groups: [LOOPBACK_INTERFACE]
            - id: 100
              description: Anycast-RP
              ip_address: 10.1.101.1/32
              interface_groups: [LOOPBACK_INTERFACE]

Example 3: Loopback with inline OSPF/PIM configuration and VRF membership

nxos:
  devices:
    - name: BORDER-LEAF1
      configuration:
        interfaces:
          loopbacks:
            - id: 0
              description: Router-ID-Underlay
              ip_address: 10.1.100.5/32
              ospf:
                process: "1"
                area: 0.0.0.0
                network: p2p
              pim:
                sparse_mode: true
            - id: 10
              description: VRF-BLUE-Loopback
              vrf: BLUE
              ip_address: 192.168.1.1/32
              ipv6_addresses:
                - address: 2001:db8:1::1/128
                  type: primary