It's been quiet lately, so I thought I'd wake you up for the holidays!
{10.4.2} of draft 21 defines the address types "ipv4" and "ipv6", but
leaves the door open for extensions to define additional address types.
The Network Map service {11.2.1} returns the prefixes in each PID grouped
by address type, as in
"PID2": { "ipv4": ["198.51.100.128/25"] }
What should a client do if the ALTO server returns an address type that
the client does not recognize? As far as I can tell, the protocol doesn't
say. If a client completely rejects a Network Map because it has an
unknown address type, that will make it difficult to add extensions.
{8.3.8} does say, "ALTO implementations MUST ignore unknown fields when
processing ALTO messages." That could be interpreted as meaning "the
client should ignore unknown address types." But you could also interpret
that as only applying to JSON dictionaries whose field names are defined
by the protocol, such as "meta" and "capabilities".
So what about explicitly saying that clients should ignore unknown address
types in the Network Map? Perhaps by adding the following paragraph to
the end of {11.2.1.6}:
"An ALTO client MUST ignore any EndpointAddressGroup whose address type it
does not recognize. If as a result a PID does not have any address types
known to the client, the client still MUST recognize that PID name as
valid, even thought the client does not know what endpoints it contains."
- Wendy Roome
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