# fergal

An 8-port SFP+ switch running OpenWrt, bought to sit in front of
[`portcullis`](portcullis.md) at Nikhef. It is physically at home for now, on the bench alongside
`portcullis` while that box is staged.

- **Source:** firmware built by this flake — [`openwrt/default.nix`](../../../openwrt/default.nix)
- **Host:** bare metal
- **OS:** OpenWrt (snapshot), configured through UCI rather than RouterOS or a UniFi controller

## Hardware

| Component | Inventory |
|---|---|
| Platform | XikeStor SKS8300-8X; the board itself is branded ONTi ONT-S508CL-8S |
| SoC | Realtek RTL9303 (MIPS 34Kc) |
| Memory | 512 MB |
| Storage | 32 MiB SPI NOR (`spi0.0`) |
| Network | 8×SFP+ (`lan1`…`lan8`) |

## Role

`portcullis`'s 10G switch. Nothing else depends on it, and it is not part of the home fabric — it
is expected to travel to Nikhef with `portcullis` rather than stay behind.

While staged at home it hangs off jim's spare SFP+ port, so `portcullis` can reach the home `hi`
VLAN over 10G: `lan1` uplinks to jim's `sfp-spare`, `lan2` goes to `portcullis`, and the other six
cages are empty. See [the home switches](../home/switches.md) for the fabric it borrows.

## Network assignments

fergal has no assignments — it is not managed by the flake. Its management address is
`192.168.64.30` on the home `core` VLAN, set in UCI as `network.lan`, with no DNS record; reach it
as `ssh root@192.168.64.30`.

## VLAN configuration

One bridge (`switch`), with VLAN 1 as the untagged PVID on every port — that's the native VLAN on
jim's `sfp-spare`, and `switch.1` is where fergal's own management address lives. `hi` (100) and
`lo` (110) are **tagged** members of every port, so a box on any cage can pick them up:

```
uci show network | grep bridge-vlan
```

Tagging all eight rather than just `lan1`/`lan2` keeps a spare cage usable without a reconfigure;
there is nothing sensitive behind it while fergal is on the bench.

**Jumbo frames pass, despite what `ip link` says.** Every DSA port and the `switch` bridge read
`mtu 1500`, but the RTL9303 forwards between ports in hardware and isn't bound by those — a
`ping -M do -s 8972` from `portcullis` to the `hi` VIP crosses fergal intact, which is what makes
the 9000-MTU `hi` VLAN usable over this path. The 1500 does apply to traffic punted to the CPU,
i.e. fergal's own management on `switch.1`.

## Firmware

The image is built by this flake — see [OpenWrt images](../../deployment.md#openwrt-images) for the
outputs and the feed pin. Packages are baked into the image, so adding tooling means editing
[`openwrt/default.nix`](../../../openwrt/default.nix) and reflashing rather than installing on the
box.

### Flash layout

A single 32 MiB SPI NOR chip (`spi0.0`, 64 KiB erase blocks). `kernel` and `rootfs` are
sub-partitions of `firmware`, and OpenWrt adds `rootfs_data` as the JFFS2 overlay after a real
flash.

| Partition | Device | Offset | Size |
|---|---|---|---|
| `u-boot` | `mtd0` | `0x000000` | 1 MiB |
| `board-info` | `mtd1` | `0x100000` | 192 KiB |
| `syslog` | `mtd2` | `0x130000` | 832 KiB |
| `firmware` | `mtd3` | `0x200000` | 30 MiB |

**`board-info` is irreplaceable.** It holds the unit's MAC addresses (`[vlanmac]` / `[cpumac]`), its
`[license]` hash, the stock boot pointers and an SSH host key — only about 1.3 KiB of it is
non-blank, and none of it can be regenerated. A full dump of all four partitions, taken before
OpenWrt was flashed, is kept outside this repo — 33 MB of images, with per-partition checksums and
restore notes. Never write `u-boot` or `board-info` without a confirmed serial/TFTP recovery path.

### Flashing notes

The procedure itself is in [`openwrt-flash.md`](../../openwrt-flash.md); what follows is specific to
this board.

Stock u-boot boots `flash:/nos.img` from a JFFS2 filesystem, so OpenWrt's sysupgrade image is
itself a JFFS2 image containing `nos.img` rather than a raw kernel + squashfs. Two things bite when
flashing from an initramfs, as during the initial install:

- **`sysupgrade -c` does not work.** It needs `/overlay/upper/etc`, which doesn't exist when running
  from RAM, and it aborts *after* `mtd erase firmware` has already run — leaving the box with no
  bootable firmware until the job is finished. Pass the config as an explicit tarball instead
  (`tar czf`, then `sysupgrade -f <tarball> …`).
- **The working management address may not be in UCI.** If it was set by hand with `ip` while UCI
  still held the stock address, the box comes back unreachable. Write it into `network.lan` and
  commit before flashing.

Neither applies to an ordinary flash-to-flash upgrade, where `sysupgrade` keeps `/etc/config` and
the files listed in `/lib/upgrade/keep.d/` by default. Dropbear host keys are regenerated by a flash
that doesn't preserve them, so clear the old `known_hosts` entry afterwards.

## Notable config files

- [`openwrt/default.nix`](../../../openwrt/default.nix) — image definition and baked-in package list.
