DHCP Option 121 (RFC 3442) — Encoder + Decoder

Encode: enter routes as CIDR gateway, one per line. Example: 10.10.10.0/24 192.168.1.1
Decode: paste the HEX blob (raw or Zyxel AA:BB:.. form). It will output routes.

Encode routes → HEX

Zyxel HEX (colon separated)
Raw HEX
Windows DHCP bytes (0x..,0x..)

Encoder breakdown

Each route encodes as: [prefixLen][destNetworkBytes][gateway(4 bytes)]
# Input Prefix Dest bytes GW bytes Route HEX
No routes yet.

Decode HEX → routes

Decoded routes (CIDR gateway)

Decoder breakdown

Parser walks the stream: prefix → ceil(prefix/8) dest bytes → 4-byte gateway.
# Prefix Destination Gateway Consumed HEX
Paste HEX and click Decode.