[Dnsmasq-discuss] [PATCH] DHCPv6 - network booting 'address in use'

[Harald Jensas]

On 9/16/21 21:32, Petr Menšík wrote:
> Hi!
> 
> There is also bug on Red Hat bugzilla [1] for this issue, which contains
> a bit more comments about it.
> 
> I would make short summary here. The problem is client on the same
> machine with the same DUID and mac address requests IPv6. Before it
> processes Advertisement, it requests IPv6 again, this time with
> different IAID.
> 
> So there are two different request, the only difference are IAID and
> requested options set. Now if the second request gets processed first,
> it assigns lease first. Consider --dhcp-sequential-ip is in use.
> Then first request processes advertisement and attempts to request the
> same IP.
> Now it would fail.
> 
> How should it react according to RFC 8415 [2]? In current situation,
> dnsmasq responds with No address available error. Could it instead
> respond with different address? How should the server and the client
> behave, when advertised address is no longer available? Is it broken on
> both sides?

I think Petr may be on to something with "Could it instead respond with 
a different address?". It seems this is ok based on rfc8415 18.3.2 [1] 
which states the following:
"""
    The server MAY assign different addresses and/or delegated prefixes
    to an IA than those included within the IA of the client's Request
    message.
"""

With the below patch I got dnsmasq to reply with a new address to the 
request with the already leased address. This makes dnsmasq behave 
similar to kea-dhcp6, see Bugzilla comments #36 and #41 [2][3] which 
also contain a pcap files.

I tested this with both static and dynamic configuration, 
"sequential-ip" enabled, and it seems to work.

If I change the 'dhcp-host' entry in the static config to contain just 
*one* address, it fails as expected with:
   option: 13 status  2 address unavailable 

   option: 13 status  2 no addresses available


I tested with the following configurations ...

Static config:
--------------
log-dhcp
port=0
dhcp-range=set:range0,2001::,static,64,10m
dhcp-host=00:84:ed:01:00:10,tag:dhcpv6,client.localdomain,[2001::20],[2001::21],[2001::22],[2001::23]
dhcp-sequential-ip
# dhcpv6s for Client System Architecture Type (61)
dhcp-match=set:efi6,option6:61,0007
dhcp-match=set:efi6,option6:61,0009
dhcp-match=set:efi6,option6:61,0011
dhcp-option=tag:efi6,option6:bootfile-url,tftp://[2001::2]/shimx64.efi

Dynamic config with sequential-ip:
---------------------------------
log-dhcp
port=0

dhcp-range=set:range0,2001::10,2001::100,64,10m
dhcp-sequential-ip
# dhcpv6s for Client System Architecture Type (61)
dhcp-match=set:efi6,option6:61,0007
dhcp-match=set:efi6,option6:61,0009
dhcp-match=set:efi6,option6:61,0011
dhcp-option=tag:efi6,option6:bootfile-url,tftp://[2001::2]/shimx64.efi



Regards,
Harald

[1] https://datatracker.ietf.org/doc/html/rfc8415#section-18.3.2
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1998448#c36
[3] https://bugzilla.redhat.com/show_bug.cgi?id=1998448#c41
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