[rrg] Fundamental objections to a host-based scalable routing solution

[Luigi Iannone]

William Herrin wrote:
> On Mon, Nov 24, 2008 at 11:15 PM, Robin Whittle <rw at firstpr.com.au> wrote:
>   
>>> By contrast, a multiple-LOC multihomed host could detect the failure
>>> of one of its LOCs (the one associated with the failed link) within a
>>> few hundred milliseconds and switch to using just the LOCs which still
>>> work. Detection is straightforward: if you're round-robining through
>>> the available LOCs as you send packets, the failed LOC sets are the
>>> ones that stop reliably returning responses.
>>>       
>> I can't see how every multihomed host could be required to
>> continually test reachability with extra packets, or that it would be
>> good to have each host sending out packets through multiple ISP links
>> as a means of detecting an outage.
>>     
>
> Who said anything about sending extra packets? The payload packets are
> the test. The acks (or their absence) are the response to the test.
>
>   


This if you assume symmetric traffic (e.g., TCP) and symmetric routing
(i.e.,  A -> B = B -> A).
IMHO you can't make this assumption.

Cheers

Luigi