JUNIPER UPLINK PLANNING
Juniper EX3400 Optics and Compatibility Guide
A practical reference for assigning EX3400 SFP, SFP+, QSFP+ and Virtual Chassis ports without treating form factor as proof of compatibility.
Start by assigning each uplink port a role
Every EX3400 model provides four autosensing front-panel uplink ports that support 1GbE SFP, 10GbE SFP+ or a mixture of the two. Two rear QSFP+ ports support 40GbE media and are configured as Virtual Chassis ports by default.
The front ports are network ports by default and can be converted to Virtual Chassis ports. The rear QSFP+ ports can be converted from Virtual Chassis ports to network ports. This flexibility is useful, but a change in port role must be part of the configuration and rollback plan.
| Port group | Physical media | Default role | Key boundary |
|---|---|---|---|
| Front uplinks 0-3 | SFP or SFP+ | Network ports | Supports four 1GbE, four 10GbE or a mixture; 1GbE SFP cannot form Virtual Chassis. |
| Rear uplinks 0-1 | QSFP+ | Virtual Chassis ports | Can become 40GbE network ports after explicit configuration. |
| Access ports | RJ-45 on T/P models | Network access | PoE exists only on PoE-capable P models, not on T models. |
Select media from reach, fiber plant and the current HCT
Use Juniper's Hardware Compatibility Tool for the current EX3400 transceiver list. The host port, optic PID, Junos release, connector, wavelength, fiber type and link budget must agree. “SFP+” alone does not establish support.
Multimode short reach
Use an HCT-listed short-reach optic where the installed multimode fiber and calculated link loss fit the published limits.
Single-mode long reach
Select the listed LR, ER or other class only after checking wavelength, distance, receiver limits and total attenuation.
Direct attach copper
Use a listed passive DAC for short in-rack or adjacent-rack links where both endpoints support the exact cable PID.
Juniper recommends Juniper-supplied optics and cables. Its documentation states that JTAC provides complete support for Juniper-supplied modules and cables, while third-party media can limit troubleshooting support.
SFP+ and QSFP+ DAC planning
| Cable class | Published use | Speed | Planning rule |
|---|---|---|---|
| SFP+ passive DAC | In-rack or adjacent-rack links | Up to 10Gbps | Juniper documents 1m, 3m, 5m and 7m passive cables; verify the exact PID in HCT. |
| QSFP+ passive DAC | EX3400 Virtual Chassis or 40GbE network connection | Up to 40Gbps | Confirm both endpoints, cable length and whether the rear port remains a VCP. |
DAC is not a generic substitute for optics. A cable integrates both endpoint modules, so the full assembly must be supported by both devices and the intended port mode.
Virtual Chassis changes the uplink budget
Up to ten EX3400 switches can operate as one Virtual Chassis. Rear QSFP+ ports are the natural starting point because they are VCPs by default. Front SFP+ ports can also be configured as VCPs, but 1GbE SFP transceivers cannot be used to form the Virtual Chassis.
Before converting a rear QSFP+ port to ordinary 40GbE networking, verify that the remaining ports preserve the intended topology, redundancy and split-detection design. Record cable PIDs and member-to-member connections so a failed cable can be replaced without guessing.
Compatibility checklist
- Identify the switch: record exact EX3400 model, Junos release, power supplies and airflow.
- Assign the port role: network, Virtual Chassis or reserved.
- Choose speed and media: 1GbE SFP, 10GbE SFP+, 40GbE QSFP+ or DAC.
- Check HCT: verify the exact optic or cable PID against EX3400 on the day of purchase.
- Validate the plant: connector, fiber type, wavelength, distance, attenuation, patch panels and receiver limits.
- Confirm peer support: the remote switch or server must support the same media and signaling.
- Test: verify link, errors, DOM readings, member state and redundancy before production acceptance.
Related EX3400 and media records
Review exact model and cable identities before building the final uplink bill of materials.
Official manufacturer sources
- EX3400 system overview
- EX3400 network cable and transceiver planning
- Juniper Hardware Compatibility Tool for EX3400
- EX3400 official documentation hub
This independent compatibility guide is not a Juniper publication and does not claim partner authorization. The HCT is the controlling current source for supported media; verify it and the installed Junos release before ordering.