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I tried IPv6 support in Amazon EC2 VPC. Amazon EC2 VPC uses RA and DHCPv6 for IPv6 addressing.

Problem

AFAIK, a EC2 instance receives an RA message with manged flag, then it sends a DHCPv6 solicit message to ff02::1:2. DHCPv6 server in VPC is expected to respond to solicit massages.

In case of dhclient, everything works well. But in case of systemd-networkd (or dhcpcd), it seems that DHCPv6 server ignores solicit messages (that is, no DHCPv6 advertise message appears in packets captured by tcpdump)

Environment

  • Linux (coreos 1339.0.0, kernel 4.10.1)
  • systemd 231
  • dhcpcd 6.11.5 (by docker container with host-network and privileged mode)
  • dhclient 4.3.5 (by docker container with host-network and privileged mode)

My suspicion

DHCPv6 solicit messages sent by systemd-networkd and dhcpcd have rapid-commit option. On the other hand, those sent by dhclient do not have rapid-commit option. The presence of that option is the most notable difference I've found in the solicit messages from dhclient and the others.

Question

In case of systemd-networkd (or dhcpcd), how to disable rapid-commit option ? I want to use systemd-networkd for network management.

takaomag
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    If rapid commit is enabled and the server supports it, you won't see an advertise message; the server will skip directly to reply. – Michael Hampton Mar 15 '17 at 02:49
  • I guess DHCPv6 server in VPC does not support rapid commit. Simply discard solicit messages. – takaomag Mar 15 '17 at 03:54
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    That's an RFC violation right there. – Michael Hampton Mar 15 '17 at 03:54
  • Do you mean DHCPv6 server in VPC is not RFC compliant ? (https://tools.ietf.org/html/rfc3315#section-17.2.1) If so, I have to ask amazon to support it. But now, is there any workaround for this problem ? – takaomag Mar 15 '17 at 04:13
  • @MichaelHampton The behaviour seems to be allowed by RFC, as per link in above comment. – jbg Feb 23 '22 at 05:38

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