Talk:Network Environment

= Stages =

== Stage descriptions ==

BCCD goes through the following network configuration stages:

# Live mode
## Initial boot:
### Try to obtain an IP address from a BCCD DHCP server
### If no BCCD DHCP servers are available, obtain an IP address from any DHCP server
## Head node: Upon user request, start DHCP server that will answer requests '''only''' from other BCCD systems
# Liberated mode
## Initial boot:
### Try to obtain an IP address from a BCCD DHCP server
### If no BCCD DHCP servers are available, obtain an IP address from any DHCP server
## Diskless boot: Upon user request, start DHCP server that will answer requests from diskless BCCD systems on '''only''' a given interface

Open questions:

# Can <b><code>bccd-reset-network</code></b> be rewritten to produce <code>systemd.network</code> configuration files via templates for each stage?
# How do we detect that a BCCD DHCP server has ''not'' responded to a client, and obtain an address from any DHCP server?


Answered questions:

# Should we continue using <code>bccd-identifier</code> or switch to using the standard [https://www.isc.org/wp-content/uploads/2017/08/dhcp41options.html <code>vendor-class-identifier]</code> that can be provided via <code>[https://www.freedesktop.org/software/systemd/man/systemd.network.html#VendorClassIdentifier= systemd.network]</code>? <b><code>vendor-class-identifier</code> confirmed to work</b>. <code>dhcpd.conf</code> snippet:
<pre>
# dhclient on live BCCD systems will set this identifier
class "bccd-nodes" {
  match if option vendor-class-identifier = "bccd-client";
}

# Anything else, including PXE boot, will not
class "pxelinux-nodes" {
  match if option vendor-class-identifier != "bccd-client";
}
</pre>
# How do we have both a static (i.e. 192.168.3.1/24) and DHCP address on one interface, with a DHCP server listening on the static (192.168.3.1/24) address? '''Supply an <code>Address</code> stanza in addition to a <code>Network</code> stanza with DHCP set'''

== Stage configuration ==

Current testing files:

* Head node
** eth0
*** <code>/etc/systemd/network/10-dhcp-eth0.network</code>
<pre>
[Match]
Name=eth0

[Network]
DHCP=yes
</pre>
*** or having a DHCP and static address:
<pre>
[Match]
Name=eth0

[Network]
DHCP=yes

[Address]
Address=192.168.3.1/24
</pre>
** <code>/etc/systemd/network/20-static-eth1.network</code>
<pre>
[Match]
Name=eth1

[Network]
Address=192.168.3.1/24
DHCP=no
</pre>
* Client node
** <code>/etc/systemd/network/10-dhcp-eth0.network</code>
<pre>
[Match]
Name=eth0

[Network]
DHCP=yes

[DHCP]
VendorClassIdentifier=bccd-client
</pre>

DHCP configs:

* Head node should use <code>vendor-class-identifier</code> to identify clients but should still send <code>bccd-identifier = "bccd-server"</code> to clients
* Head node can also match both <code>vendor-class-identifier</code> and <code>bccd-identifier</code>:
<pre>
class "bccd-nodes" {
  match if (option vendor-class-identifier = "bccd-client") or
    (option bccd-identifier = "bccd-client");
}
</pre>
* BCCD clients should require <code>bccd-identifier</code> (from server) but send <code>vendor-class-identifier = "bccd-client"</code>, set in <code>dhclient.conf</code> (for stage detection) and systemd config file for actual network configuration

= systemd notes =

== systemd commands ==

; '''Restart networking''' : <code><b>systemctl</b> restart systemd-networkd</code>
; '''Networking status''' : <code><b>networkctl</b></code>

== systemd tricks ==

* Move <code>/etc/network/interfaces</code> out of the way to ensure that regular network setup doesn't occur
* Interface files need to have a numeric prefix and a <code>.network</code> suffix (i.e. <code>/etc/systemd/network/<b>10</b>-static-eth0<b>.network</b></code>

= Troubleshooting =

== RTNETLINK answers: File exists ==

If you get an error like this:

<pre>
RTNETLINK answers: File exists
Failed to bring up eth1.
</pre>

Try flushing that interface and replumbing it:

<pre>
$ sudo ip addr flush dev eth1
</pre>

== Getting a previous IP address ==

If you run <code>dhclient</code> and it just decides to pick a previous IP address (it might even do a DHCPREQUEST, but not a DHCPDISCOVER):

# Release the IP address: <code>dhclient -r</code>
# Shutdown the interface: <code>ifconfig <i>nic</i> down</code>
# Try doing DHCP again

= mdns notes =

* Subscribers use multicast address 224.0.0.251, port 5353 (not 53)
** Uses <code>.local</code> domain
* Hostnames
** BCCD node could see if anyone else has registered bccd0.local and become head node if not
** _bccd.local service could be registered with a list of all active BCCD clients ([http://www.dns-sd.org/ServiceTypes.html registration link])
* Uses back-off protocol for conflict resolution