PD broken in v4.3.2? prefix6 start prefix is outside the subnet

Christian Kratzer ck-lists at cksoft.de
Wed Jul 15 08:59:31 UTC 2015


On Tue, 14 Jul 2015, Shawn Routhier wrote:
> We did make a change to restrict prefix6 to be within the subnet.
> We are re-consdiering this change and would be interested in hearing
> peoples comments.  Note that we are in the process of wrapping up
> the current work on the releases so comments should be sent to the
> list soon.
> The argument for requiring the PD to be within
> the subnet is that the subnet describes the topology of the network
> and that it should map the routing of the network.  So to get to
> a PD one would route to the given subnet.

a couple of quick points on this:

1. this would require one to enlargeng the access network to emcompass
the whole pool of prefixes one wishes to delegate. This would definetely
be considered a broken design.

2. Just having the network large enough would still only route towards
the net.  This would not help with getting the ultimate next hop for the
assigned prefix resolved.

3. ipv6 relay agents on routers that support PD sniff the traffic and
transparently add the route to the delegated prefix to the correct next hop.

Such a change would definetely be broken and would have to be backed out.

I have not researched the actual facts myself yet.  Just judginge from
the description in the previous postings.

> However I do think you are confused about the configuration file
> showing class support from the KB article.  I have tried the three
> configuration files in that kb article and all of them seem to work
> correctly for me with the prefixes being within the subnet.
> The second example you give would appear to have issues though
> they could be fixed by changing the subnet length from 64 to 56.


Christian Kratzer                   CK Software GmbH
Email:   ck at cksoft.de               Wildberger Weg 24/2
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