Add rack subnet to wicket RSS config

[rcgoodfellow]

Wicket currently uses a constant rack subnet for RSS

omicron/wicketd/src/rss_config.rs

Lines 664 to 687 in 5d08d2f

	Ok(bootstrap_agent_client::types::RackNetworkConfigV2 {
	rack_subnet: RACK_SUBNET.net(),
	infra_ip_first: config.infra_ip_first,
	infra_ip_last: config.infra_ip_last,
	ports: config
	.iter_uplinks()
	.map(|(switch, port, config)| {
	build_port_config(switch, port, config, bgp_auth_keys)
	})
	.collect(),
	bgp: config
	.bgp
	.iter()
	.map(|config| BaBgpConfig {
	asn: config.asn,
	originate: config.originate.clone(),
	checker: config.checker.clone(),
	shaper: config.shaper.clone(),
	})
	.collect(),
	//TODO bfd config in wicket
	bfd: vec![],
	})
	}

For cluster deployments, this needs to be configurable so that racks within the cluster can eventually be joined together in a multirack setup under a single control plane.

This cannot be just any prefix. It has to follow the model in RFD 63: IPv6 Addressing

In particular the rack portion of the prefix in the leading 2 octets of the 4th segment cannot be zero. From the latter part of the section linked above

we will need some number of addresses for service discovery itself. If we assume that these may be Cell or Availability Zone-wide, then our plan is to take one of the rack /56 entries and reserve it for this purpose. This /56 is called the services prefix.

This will need to be validated by wicket before starting RSS as the calamity will ensue otherwise.

[rcgoodfellow]

I've taken the prefix fd00:17:01:0d00::/56 for a spin in a4x2 and the control plane comes all the way up.

[rcgoodfellow]

Something we should consider is making this an optional wicket field. If it is not specified then the 40 bits after fd are random, and the rack identifier is 01.