[OLSR-users] duplicate IP behaviour

[Jim Forster]

On Feb 13, 2006, at 9:53 AM, Bernd Petrovitsch wrote:

> On Sun, 2006-02-12 at 20:59 +0100, Kosta Welke wrote:
>> Andreas Tønnesen wrote:
>>> I agree that the best solution might be that olsrd exits when  
>>> encountering
>>> a IP duplicate.. but I'm not 100% sure(perhaps this should be yet  
>>> another
>
> AFAIK behaviour on IP duplicates is at best "undefined". So best is to
> avoid it (and fix up your IP assignments scheme. If the scheme
> allows/produces duplicated IPs, please bugfix it or throw it away).
> Apart from the below situation, where the net actually identifes
> duplicated IPs, what happens if the duplicated IPs are not detected?
> This may not happen today with current implementation of olsrd (since
> one node knows "always" the whole net) AFAICS but in the future?

Duplicate IP addresses are sometime useful for multiple instances of  
the same service (especially UDB-based services) and the result is  
sometimes called 'anycast'.   I'm a little fuzzy on some of the bits,  
but here's an example:  several of the root names servers on the  
Internet are deployed this way, and purposely given the same IP  
address.   They also have the same data.  I think the way they do it  
is the hosts simply inject their own /32 address into their IGP  
(usually OSPF),   DNS resquests will then go to the closest instance  
of that service.  The /32 address is also passed into the BGP  
routes.   Of course, there must be agreement by the backbone  
operators to take individual /32 routes but after that things work out.

   -- Jim