Junos Interface Configuration Generator

Generate Junos set-format interface configuration: physical properties, units, VLAN tagging, IPv4/IPv6 addressing and description conventions.

Config generator Juniper / Junos Runs in your browser
ge-, xe-, et-, ae- or irb.
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Result

Interface
ge-0/0/1.0
Tagging
802.1Q VLAN 100
IPv4
10.20.30.1/24
MTU
1514 bytes
1500 byte IP MTU equivalent
Junos configuration (set format)
set interfaces ge-0/0/1 description "CORE-UPLINK-TO-SW01"
set interfaces ge-0/0/1 mtu 1514
set interfaces ge-0/0/1 vlan-tagging
set interfaces ge-0/0/1 unit 0 vlan-id 100
set interfaces ge-0/0/1 unit 0 description "CORE-UPLINK-TO-SW01-U0"
set interfaces ge-0/0/1 unit 0 family inet address 10.20.30.1/24
set interfaces ge-0/0/1 unit 0 family inet6 address 2001:db8:1e:1e::1/64
Verification
show configuration interfaces ge-0/0/1
show interfaces ge-0/0/1.0 terse
show interfaces ge-0/0/1 extensive | match "error|drops|MTU"
ping 10.20.30.1 count 3
Rollback
delete interfaces ge-0/0/1 unit 0
commit confirmed 5
MTU accounting differs
Junos MTU counts the Ethernet header, so an MTU of 1514 gives a 1500-byte IP MTU. Cisco counts the IP MTU instead. Configuring 1500 on Junos to match a Cisco neighbour actually creates a 14-byte mismatch - a classic cause of OSPF adjacencies that stick in ExStart.
Tagging modes
vlan-tagging is a physical-interface property and cannot be combined with an untagged unit on the same interface in most Junos releases. Use flexible-vlan-tagging when you need both tagged and untagged units.

About Junos Interface Configuration Generator

Junos separates the physical interface from its logical units, which is cleaner than the Cisco subinterface model once you are used to it - and unforgiving about where a property belongs. This generates a complete, commit-safe interface stanza in set format.

Description conventions that pay off

Interface descriptions are the cheapest documentation in a network and the only kind that is always current. A consistent scheme — role, far-end device, far-end port, circuit reference — turns show interfaces descriptions into a usable topology map and makes automated inventory possible. It also removes the most common cause of a wrong-port change: guessing what a port is for from its address.

Physical versus unit properties

vlan-tagging, mtu and encapsulation belong to the physical interface. Addresses, vlan-id and per-unit filters belong to the unit. Putting a family or an address at the physical level is the most common syntax error when moving from IOS. Unit 0 is conventional for untagged or single-VLAN configuration; matching unit number to VLAN ID is a widespread convention worth adopting for readability.

Common use cases

  • Turning up a new tagged uplink or customer handoff.
  • Adding IPv6 to an existing routed interface.
  • Producing a reviewable change with matching rollback for a change window.

Edge cases and gotchas

  • Always use commit confirmed on remote devices - a lost management path rolls back automatically.
  • Junos MTU includes the 14-byte Ethernet header; Cisco does not.

Frequently asked questions

Why does my address configuration not commit?
It is almost certainly at the physical level instead of under a unit, or the unit has vlan-id set on an interface without vlan-tagging enabled.
What MTU matches a Cisco 1500?
1514 on Junos for a standard Ethernet interface. Add 4 bytes per VLAN tag if the interface is tagged.