ISATAP

Deprecated
Packet-in-packet technology
Mostly historical
Used within one site, not an Internet Technology
“v6 islands within a v4 ocean”
Treats the v4 network as NBMA
ISATAP devices must be dual stacked
Adds 20-bytes of overhead
Works as long as v4 routing works
Stateless

Theory

Use v4 connectivity to emulate a NBMA network. Wrap the v6 packet inside v4.

┌───────────┬───────────┐
│ v6-packet │ v4-header │ ───────►
└───────────┴───────────┘

Router ISATAP

         v6 only             v4 only             v6 only         
         ┌─────┐       ┌─────────────────┐       ┌─────┐         
         ▼     ▼       ▼                 ▼       ▼     ▼         
┌────────┐     ┌───────┐     ┌─────┐     ┌───────┐     ┌────────┐
│client-1│     │   R1  │     │ R2  │     │   R3  │     │client-2│
│   v6   ├─────┤ v4/v6 ├─────┤  v4 ├─────┤ v4/v6 ├─────┤   v6   │
└────────┘     └───────┘     └─────┘     └───────┘     └────────┘
                     ISATAP           ISATAP
                      Interface        Interface

Client ISATAP

                           v4 only                           
               ┌─────────────────────────────┐               
               ▼                             ▼               
┌────────┐     ┌─────┐     ┌─────┐     ┌─────┐     ┌────────┐
│client-1│     │ R1  │     │ R2  │     │ R3  │     │client-2│
│ v4/v6  ├─────┤  v4 ├─────┤  v4 ├─────┤  v4 ├─────┤  v4/v6 │
└────────┘     └─────┘     └─────┘     └─────┘     └────────┘
      ISATAP                                     ISATAP      
       Interface                                  Interface

ISATAP interface in v6

All ISATAP interfaces look like this. The giveaway is 0000:5EFE in the host portion.

If a router sees a v6 destination that looks like this, it’s an ISATAP packet.

           64 bits                32 bits        32 bits     
┌─────────────────────────────┬──────────────┬──────────────┐
│       Global Unicast        │  0000:5EFE   │ IPv4 Address │
│           Prefix            │              │on ISATAP Link│
└─────────────────────────────┴──────────────┴──────────────┘