Big Temporary Networks

Wed Sep 19 07:24:53 UTC 2012

Op 18-9-2012 22:50, William Herrin schreef:
> On Tue, Sep 18, 2012 at 4:31 PM, Nick Hilliard <nick at foobar.org> wrote:
>> On 18/09/2012 21:24, William Herrin wrote:
>>> IPv6 falls down compared to IPv4 on wifi networks when it responds to a
>>> router solicitation with a multicast (instead of unicast) router
>>> advertisement.
>> You mean it has one extra potential failure mode in situations where radio
>> retransmission doesn't deal with the packet loss - which will cause RA to
>> retry.  "Fall down" is a slight overstatement.
> Potayto, potahto. Like I said, I have no interest in defending IPv6.
> But I'm very interested in how to implement an IPv6 network that's as
> or more reliable than the equivalent IPv4 network. That makes me
> interested in the faults which get in the way.
>
> Regards,
> Bill Herrin
>
Yes, radvd has a configuration option to send unicast packets. But I 
think the effects are slightly overstated.

Unless someone fudged the lifetime counters on the ra config nobody will 
ever notice a RA getting lost. Once every few seconds a RA message will 
be sent and it will be valid for atleast a couple of minutes. Within 
that time there will be multiple RA announcements, and unless you missed 
5 minutes of RA advertisements everything is fine.

And if you do miss 5 minutes of RA multicast traffic, really, you have 
bigger problems. I see network stacks springing to life in the space of 
3 seconds on the 1st message I send out. That's pretty stellar, and 
faster then some clients perform the DHCPv4 request.

Also note that some wifi networks eat DHCPv4 broadcasts too, which is 
pretty much the same deal as what you are referring to above. They will 
retry the DHCPv4 request, and so do client that perform router 
sollicitation requests. No different.

And if the wifi network is so bad that you have icmp and udp dropping 
like mad, I doubt anybody would want to use it. You are more likely that 
they will disable wifi altogether and use 3g. The 2.4Ghz wifi band is so 
crowded now that this has become the effective standard. Unless you are 
a happy camper that actually has a wifi card that supports the 5Ghz 
band. Which is far too uncommon in phones and tablets. boo.

Cheers,

Seth