Address formats

Atlas derives each private IPv6 address from IDs. No service looks up an address in a table. This page is the reference for each layout.

Rules for every layout

Each field starts on a 16-bit boundary, so you can read the IDs from the address. The first hextet gives the address type, and the second hextet gives the region.

The tenant ID has 32 bits. A VM number and a WireGuard peer number have 16 bits each and use the last hextet.

Padding fields are zero. They hold space for later fields. Do not use them.

Prefix	Use
fdaa::/16	VM mesh addresses and the Atlas address
fdab::/16	Host wg0 addresses
fdac::/16	WireGuard gateway peers

VM mesh address

fdaa : region : tenant (32 bits) : padding (48 bits) : VM number

Example: vm-42-0007 in region 1 is fdaa:1:0:2a::7.

The VM name is vm-<tenant ID>-<VM number>. Each tenant has its own counter, so a VM number is unique only within its tenant. Each tenant has the /64 fdaa:<region>:<tenant>::/64. A tenant can have VM numbers from 1 to 65,535. Atlas refuses a larger number.

Atlas address

fdaa : region : 0 : 0 : ffff : ffff : ffff : ffff

The Atlas address is in tenant 0 and has all padding bits set. No VM can have this address.

Host wg0 address

fdab : region : low 96 bits of the host UUID

Example: fdab:1:7f90:766a:8d2c:2f76:8d76:2045. This layout has no tenant or VM field.

WireGuard gateway peer

fdac : region : node : tenant (32 bits) : padding (32 bits) : peer number

Example: peer 9 of tenant 42 on wireguard-002 in region 1 is fdac:1:2:0:2a::9.

The node field comes before the tenant. Then each node owns one /48, and a host can send the replies for that node to one VM. The node address is fdac:<region>:<node>::1. See WireGuard gateway.

IPv6 router public address

<provider block, /80 or shorter> : tenant (32 bits) : VM number

Example: block 2001:db8:1:2:3::/80 maps fdaa:1:0:2a::7 to 2001:db8:1:2:3:0:2a:7.

The public address has no padding. A /80 block has exactly 48 host bits. A mesh address with padding has no public address. See IPv6 router.

HTTP proxy auto-proxy label

label = base36((VM number << 32) | tenant)

The value has 48 bits, so a label has at most 10 characters. See OpenResty.