[Dnsmasq-discuss] Patches: Extend --bridge-interface aliasing to DHCPv6 and Router Advertisements

Simon Kelley simon at thekelleys.org.uk
Mon Oct 13 17:45:15 BST 2014

On 07/10/14 18:28, Neil Jerram wrote:
>> On 03/10/14 16:54, Neil Jerram wrote:
>>> I'd like to propose the attached patches, which extend the aliasing
>>> concept of the --bridge-interface option to DHCPv6 and Router
>>> Advertisement processing.  [...]
>> A query: the semantics you've provided for DHCPv6 are subtly different
>> than those that exist for DHCPv4.
>> In DHCPv4, the alias is absolute, eg
>> bridge-interface=eth0,tap0
>> when a packet arrives at tap0, then it is processed as if it arrived at
>> eth0, any addresses associated with tap0 are ignored.
>> With this patch, for DHCPv6, dnsmasq first attempts to find a
>> DHCP-context by using the addresses associated with tap0, and only if
>> that fails does it use the addresses associated with eth0.
> Indeed, good catch - I had missed that.
>> If this is required behaviour, I guess we should document the difference
>> in the v4 and v6 cases. If it's like that by chance, we should think
>> about if providing the same behaviour in both cases might be preferable.
> It isn’t required behaviour.  At least, for the compute host scenario
> that I am interested in, the alias interfaces will never have any IP
> addressing or contexts of their own, and also the aliased interface -
> i.e. the one that _does_ have the DHCP context - will never receive a
> packet directly itself.  Therefore, for my purposes, it would be fine
> to align the DHCPv6 behaviour precisely with the v4 behaviour.
> Logically I think the same should also apply to solicited RA
> processing, i.e. in the ND_ROUTER_SOLICIT block of icmp6_packet.
> Would you agree?

Yes, certainly.

> Finally, I guess I should also update the "One form of bridging ..."
> comment in dhcp_packet, and the man page text on --bridge-interfaces,
> to mention my scenario in addition to the BSD one.

Yes, that's well out-of-date.
> If that all sounds good to you, I'm happy to work on updating the
> patches - please let me know what you think.

Please do. Happy to have this.



> Regards,
>         Neil

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