Re: Move forward

[marcelo bagnulo <marcelo@it.uc3m.es>]

> I didn't mean including explicit signaling in the normal traffic, but
> just _looking_ at the normal traffic to see if everything still works.
> This could work by having a list of destination hosts we're
> communicating with. Each time a normal-looking packet (ie non-ICMP,
> non-tunnel, non-multicast, big enough so it's not just an ACK) goes out,
> some session state is saved and a timer is started. When the timer
> elapses (after 5 or 10 seconds or so)  without any return traffic, we do
> a "real" reachability check. So during normal traffic flow, there is no
> need for explicit or piggy-backed reachability checks. This probably
> needs some more heuristics, but I think it could work well.
> 

I agree that better and more optimal failure detection can be provided,
which could use some of these ideas.
I am more worried about MIPv6 timers though...
[...]
> > > - "If a failure   has occurred along the path, the attempt to initiate
> > >   the communication will fail and the CN will try again with another
> > >   address. Eventually, a packet from CN will reach MHH." As this is
> > >   application-dependent you can't count on this. Worse: the all-time
> > >   most popular networked application typically chokes if the first address
> > >   tried doesn't work.
> 
> > Good point. I do not have much data about how applications normally
> > behave in this case. But if this is the case, this is an issue. However,
> > AFAIK this is probably the case for IPv4 where interfaces usually have
> > only one address configured.
> 
> The number of addresses per interface isn't really an issue, I would
> think. In v4 having several addresses for a DNS name isn't all that
> unusual:
> 
> > host www.cnn.com
> www.cnn.com is a nickname for cnn.com
> cnn.com has address 64.236.24.28
> cnn.com has address 64.236.16.20
> cnn.com has address 64.236.16.52
> cnn.com has address 64.236.16.84
> cnn.com has address 64.236.16.116
> cnn.com has address 64.236.24.4
> cnn.com has address 64.236.24.12
> cnn.com has address 64.236.24.20
> 
> > However in IPv6, considering "Default
> > Address Selection mechanism" i was hoping that application used the list
> > of addresses generated by the mechanism and try to use them to
> > communicate
> 
> Actually this may make it worse, as the "best" address is always
> selected. If the "best" address is unreachable, no dice. At least with
> random or round robin you can hit reload to try again.
> 
Sorry i am probably missing something...
>From RFC 3484

6. Destination Address Selection

   The destination address selection algorithm takes a list of
   destination addresses and sorts the addresses to produce a new list.
                                                                  ^^^^
I guess that applications now obtain a list of addresses, after the
default address selection mechanism has sorted them.
Moreover, the first rule of the mechanism discards unreachable
destinations, so if one of multiple is unreachable it will be included
last.

Regards, marcelo 
> Iljitsch
-- 
marcelo bagnulo <marcelo@it.uc3m.es>
uc3m