Re: Address Family Support in OSPFv3

[Russ White <[e-mail]>]

>     - The multiple instance approach has the advantage of not requiring
>       as much new invention (as Quaizar pointed out). The separation of
>       link state databases and configuration is already there (since it
>       each address family has a separate instance). However, it will still
>       require new invention if other address families are to be carried (e.g.,
>       IPv4).

I think this is the strongest argument for address families--the seperate
instance approach is going to require you to either:

-- create a new version of ospf, and run a seperate instance, finding some
way to only exchange that information relevant to the right ospf instance
on each neighbor through some means, for wach type of information you'd
like to carry

-- create new tlv's/ways of carrying information (address families) within
the data structures so you can carry then information in a way that it can
be sorted out correctly

For instance, if you have two routers:

A----B

Suppose you want to carry ipv6, foo, and ipv4 between these routers. This
would mean creating three different versions of ospf for these functions,
out of which you can distinguish, in some way, what sort of information a
specific peer is going to be passing, along with specific tlv's, etc. If,
as in the case of multicast, the information is actually in the same
format, you need to arbitrarily change the data format just to
differentiate it.

So, what you have is address families, anyway. You could argue that ospfv2
and ospfv3 are actually address families as it is, just over different
peering sessions.

So, it seems to me the question comes down to: "address families over a
single adjacency, or address families over independant adjacencies?" The
answer to that question seems very clear--address families over a single
adjacency is much easier to implement, much easier to configure and
maintain, and much more flexible.

You're not going to get away from "inventing" new packet formats for each
type of data you want to carry, sometimes with arbitrary changes just to
differentiate the data type. Why not make the arbitrary change an address
family field, and be done with it?

:-)

Russ


__________________________________
[e-mail] CCIE <>< Grace Alone