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network: clarify the relationship between RA flags and DHCPv6 modes

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In the documentation, using the term "managed" for both the RA flag and
the DHCPv6 mode is confusing because the mode is referred to as
"solicit" both in the official DHCPv6 documentation (see RFC 8415) and
in the WithoutRA option.

Furthermore, calling the other RA flag "other information" or "other
address configuration" is confusing because its official name is simply
"other configuration" (see RFC 4861 and RFC 5175) and it isn't used to
assign IP addresses.

Rewrite the documentation for DHCPv6Client and WithoutRA to make it
clear that getting the "managed" RA flag triggers the same kind of DHCP
request as WithoutRA=solicit, whereas getting the "other configuration"
RA flag triggers the same kind of DHCP request as
WithoutRA=information-request.
This commit is contained in:
Alex Henrie 2022-05-06 14:01:53 -06:00
parent ad11dd94fd
commit 0bcc6557fb
4 changed files with 18 additions and 13 deletions
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19
man/systemd.network.xml
View file

@ -2172,9 +2172,10 @@ Table=1234</programlisting></para>
<varlistentry>
<term><varname>WithoutRA=</varname></term>
<listitem>
<para>Allows DHCPv6 client to start without router advertisements's managed or other
address configuration flag. Takes one of <literal>no</literal>, <literal>solicit</literal>
or <literal>information-request</literal>. If this is not specified,
<para>Allows DHCPv6 client to start without router advertisements's
<literal>managed</literal> or <literal>other configuration</literal> flag. Takes one of
<literal>no</literal>, <literal>solicit</literal>, or
<literal>information-request</literal>. If this is not specified,
<literal>solicit</literal> is used when <varname>DHCPPrefixDelegation=</varname> is enabled
and <varname>UplinkInterface=:self</varname> is specified in the [DHCPPrefixDelegation]
section. Otherwise, defaults to <literal>no</literal>, and the DHCPv6 client will be started
@ -2507,10 +2508,14 @@ Token=prefixstable:2002:da8:1::</programlisting></para>
<term><varname>DHCPv6Client=</varname></term>
<listitem>
<para>Takes a boolean, or the special value <literal>always</literal>. When true, the
DHCPv6 client will be started when the RA has the managed or other information flag. If set
to <literal>always</literal>, the DHCPv6 client will be started in managed mode when an RA
is received, even if neither managed nor other information flag is set in the RA. This will
be ignored when <varname>WithoutRA=</varname> in the [DHCPv6] section is enabled, or
DHCPv6 client will be started in <literal>solicit</literal> mode if the RA has the
<literal>managed</literal> flag or <literal>information-request</literal> mode if the RA
lacks the <literal>managed</literal> flag but has the
<literal>other configuration</literal> flag. If set to <literal>always</literal>, the
DHCPv6 client will be started in <literal>solicit</literal> mode when an RA is received,
even if neither the <literal>managed</literal> nor the
<literal>other configuration</literal> flag is set in the RA. This will be ignored when
<varname>WithoutRA=</varname> in the [DHCPv6] section is enabled, or
<varname>UplinkInterface=:self</varname> in the [DHCPPrefixDelegation] section is
specified. Defaults to true.</para>
</listitem>

2
src/libsystemd-network/sd-dhcp6-client.c
View file

@ -1384,7 +1384,7 @@ int sd_dhcp6_client_start(sd_dhcp6_client *client) {
}
log_dhcp6_client(client, "Starting in %s mode",
client->information_request ? "Information request" : "Managed");
client->information_request ? "Information request" : "Solicit");
return client_start_transaction(client, state);
}

4
src/network/networkd-dhcp6.c
View file

@ -35,7 +35,7 @@ static DHCP6ClientStartMode link_get_dhcp6_client_start_mode(Link *link) {
if (link->network->dhcp6_client_start_mode >= 0)
return link->network->dhcp6_client_start_mode;
/* When this interface itself is an uplink interface, then start dhcp6 client in managed mode. */
/* When this interface itself is an uplink interface, then start dhcp6 client in solicit mode. */
if (dhcp_pd_is_uplink(link, link, /* accept_auto = */ false))
return DHCP6_CLIENT_START_MODE_SOLICIT;
@ -686,7 +686,7 @@ static int dhcp6_configure(Link *link) {
return log_link_debug_errno(link, r, "DHCPv6 CLIENT: Failed to %s requesting prefixes to be delegated: %m",
enable_disable(link->network->dhcp6_use_pd_prefix));
/* Even if UseAddress=no, we need to request IA_NA, as the dhcp6 client may be started in managed mode. */
/* Even if UseAddress=no, we need to request IA_NA, as the dhcp6 client may be started in solicit mode. */
r = sd_dhcp6_client_set_address_request(client, link->network->dhcp6_use_pd_prefix ? link->network->dhcp6_use_address : true);
if (r < 0)
return log_link_debug_errno(link, r, "DHCPv6 CLIENT: Failed to %s requesting address: %m",

6
src/network/networkd-ndisc.c
View file

@ -949,13 +949,13 @@ static int ndisc_start_dhcp6_client(Link *link, sd_ndisc_router *rt) {
return 0;
/* (re)start DHCPv6 client in stateful or stateless mode according to RA flags.
* Note, if both managed and other information bits are set, then ignore other
* information bit. See RFC 4861. */
* Note, if both "managed" and "other configuration" bits are set, then ignore
* "other configuration" bit. See RFC 4861. */
r = dhcp6_start_on_ra(link, !(flags & ND_RA_FLAG_MANAGED));
break;
}
case IPV6_ACCEPT_RA_START_DHCP6_CLIENT_ALWAYS:
/* When IPv6AcceptRA.DHCPv6Client=always, start dhcp6 client in managed mode
/* When IPv6AcceptRA.DHCPv6Client=always, start dhcp6 client in solicit mode
* even if the router flags have neither M nor O flags. */
r = dhcp6_start_on_ra(link, /* information_request = */ false);
break;