[Dnsmasq-discuss] Make RA_INTERVAL configureable? Deprecate old prefixes?

Simon Kelley simon at thekelleys.org.uk
Sat Jul 27 14:14:58 BST 2013


On 26/07/13 22:19, Uwe Schindler wrote:
> Hi,
>
> After some testing and reconnecting PPP connection several times: All
> works fine. It also recognizes multiple old prefixes and sends all of
> them as deprecated.
>
> Regarding the Android-Bug: I found out that I still have to enable
> the "fast" mode (which is only done in the first minute after a
> config change). The reason is: Although the prefix has a lifetime of
> 86400 on my dhcp-range, in contrast, the router itself gets a
> lifetime of 1800 secs (3 times RA_INTERVAL), the RDNS got a lifetime
> of 1200 secs (2 times RA_INTERVAL). To me this looks a bit
> inconsequent. The router itself is in my opinion the most stable
> thing of all, because its link-local-adress is used by clients. The
> DNS server should in my opinion have the same lifetime as the prefix
> / dhcp-range - or best would be to use this value:
> "dhcp-option=option6:information-refresh-time" (maybe you should send
> the dhcp's range's lease time as information-refresh-time on every
> dhcp request).

The 3 times RA_INTERVAL comes from the default given in RFC 4861, 
section 6.2.1 which also specifies an absolute maximum value of 9000 
seconds. I don't know if it's sensible to violate this RFC.
>
> I was able to fix the android bug again by reducing the re-transmit
> time by patcing the code, this time a bit more easy: I changed, as
> suggested by you, the if-statement in the function
> "new_timeout(struct dhcp_context *context, time_t now)", to always
> use the short interval of 5 - 20 secs. This solved the problem. I
> think if you add a config option to enable the fast retransmit if you
> have buggy android phones, we are fine.
>
> In addition, maybe have a separate config option to change the fast
> retransmit time (but different from RA_INTERVAL) and RA_INTERVAL
> itself (as you can do with radvd).
>

I want to try and avoid making every parameter changable, like Radv 
does. Who can tell what the parameters should be. A flag which says 
"stay in fast retransmit mode to fix buggy android" seems much more 
sensible.

Simon.

> Uwe
>
> P.S.: FYI, my DNS server address is a private IPv6 address which is
> assigned to the LAN interface in addition to the global prefix, see
> my other mail for explanation. So the DNS is stable here, stable as
> the link-local router address. I would recommend this setup also for
> router manufacturers. If the DNS server is not stable, the
> information-refresh-time in the DHCP packets should in any case be
> specified, otherwise the client never ever asks again for the DNS
> server. I checked this on windows computer.
>



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