Date: October 26, 2023 Subject: vMX Virtualization Platform (Domestic Image) Software Version: Junos OS 14.1R4.8
Juniper vMX is a virtualized version of the physical MX Series router. It typically consists of two components (VMs):
In version 14.1, the installation process was often complex, requiring specific nested virtualization support (Intel VT-x/VT-d) and specific versions of QEMU or KVM.
Repacking the jinstall-vmx-14.1R4.8-domestic.img file is typically done to enable the Internal Packet Forwarding Engine (PFE) or to set default configurations (like root passwords) so they persist across lab sessions in emulators like GNS3 or EVE-NG.
This specific version (14.1R4.8) is a "legacy" or single-node vMX image that contains both the Control Plane (vCP) and Forwarding Plane (vFP) in one file, unlike newer split-VM versions. 1. Preparation & Tools
To modify and repack the image, you need a Linux environment (Ubuntu is recommended) with the following tools: qemu-img: To convert and manage disk images. nbd-client: To mount the image as a network block device. chroot: To enter the image's filesystem. 2. The Repack Procedure jinstallvmx141r48domesticimg repack
This process involves mounting the .img file, modifying the internal boot loader to enable the PFE, and saving the changes. Step A: Mount the Image
Convert the image to a format easier to mount if necessary, though most tools can handle .img (raw) directly. Load the NBD kernel module: sudo modprobe nbd max_part=8.
Connect the image: sudo qemu-nbd -c /dev/nbd0 jinstall-vmx-14.1R4.8-domestic.img.
Identify the partitions using lsblk or fdisk -l /dev/nbd0. Usually, Junos images have multiple partitions; you are looking for the one containing /boot. Step B: Enable the Internal PFE (The "Hack")
The main reason users repack this image is to avoid running a second VM for the forwarding plane. Mount the boot partition: sudo mount /dev/nbd0p1 /mnt. Edit the /boot/loader.conf file: Add the line: vm_local_pfe="1". This forces the vMX to use its built-in forwarding engine. Date: October 26, 2023 Subject: vMX Virtualization Platform
Optional: To bypass the mandatory root password requirement on first boot, you can also modify the configuration files within the image to include a default root authentication. Step C: Finalize and Unmount Flush changes to the disk: sync. Unmount the partition: sudo umount /mnt. Disconnect the NBD device: sudo qemu-nbd -d /dev/nbd0. 3. Deploying the Repacked Image
Once repacked, the image can be imported into your lab environment.
In GNS3: Use the GNS3 Import Guide to create a new Qemu VM. Assign at least 1GB of RAM and use 1 vCPU.
Network Settings: Assign at least 12 adapters. Set the first port to e1000 or virtio-net-pci.
Verification: After booting, run show chassis fpc pic-status. If repacked correctly, Slot 0 and PIC 0 should show as Online, and ge-0/0/x interfaces will be visible. Juniper vMX on GNS3 - Brezular's Blog In version 14
From a security auditing perspective, analyzing a repack is crucial:
The repack bridges the gap between the virtual network interfaces and the physical host.
| Feature | Description |
|---------|-------------|
| Silent installation | No user interaction, pre-configured answers |
| Pre-activated / license included | May bypass license checks (⚠️ risky) |
| Size optimization | Removed docs, demos, unused locales |
| Bundled dependencies | Tools, libraries, drivers integrated |
| Registry/tweaks applied | Optimized VM params, disabled updates, telemetry off |
| Self-extracting archive | Single .exe or script-based installer |
To understand the "repack," one must first understand the dual-VM architecture of the vMX. The jinstall package is not a single bootable OS, but a container for two separate operating environments.
A "repack" of a vMX image usually occurs for the following technical reasons: