Subject: Re: [manet] Routing using IPv6

From: Richard Ogier <[email-masked]>
Date: Fri, 11 Apr 2003 07:16:10 -0700

Fred Baker wrote:

> Routing is generally a matter of creating a graph among the nodes in a
> graph - a lattice of routers with interconnection topologies - and then
> decorating the graph with prefixes. We can carry your favorite routing
> protocol in IPv4 or IPv6, and we can decorate the graph with IPv4 or IPv6
> prefixes.
>
> The only thing that comes quickly to mind is my suggestion of using OSPF V3
> last year, whose LSAs are designed around IPv6 and which identifies
> neighbors using IPv6 link local addresses.

A link-local address in IPv6 has the following format (RFC 2373):

   |   10     |
   |  bits    |        54 bits          |          64 bits           |
   +----------+-------------------------+----------------------------+
   |1111111010|           0             |       interface ID         |
   +----------+-------------------------+----------------------------+

Therefore, if the HELLO messages in OLSR and TBRPF for IPv6 
contain only link-local neighbor interface addresses, then it 
is not necessary to include the entire 128-bit IPv6 address.  
Only the interface IDs need to be included in HELLO messages. 
This can reduce overhead significantly.

In TBRPF, topology updates contain only 32-bit router IDs, for 
both IPv4 and IPv6 (similar to OSPF for IPv6), which saves a lot 
of overhead.  IPv6 addresses are advertised in separate messages, 
which can be sent less frequently.

The "IPv6 Considerations" section of the OLSR draft says:

 "All the operations and parameters described in this document used by
  OLSR for IP version 4 are the same as those used by OLSR for IP ver-
  sion 6.  However, to operate with IP version 6, the only required
  change is to replace the IPv4 addresses with IPv6 address."

Thomas, Are you really proposing to use 128-bit IPv6 addresses
in HELLOs and TC messages?  Or are you changing this in your
updated draft?  

Regards,
Richard
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---

From: Fred Baker <[email-masked]>
Date: Fri, 11 Apr 2003 10:29:43 -0700

At 07:16 AM 4/11/2003 -0700, Richard Ogier wrote:
>In TBRPF, topology updates contain only 32-bit router IDs, for both IPv4 
>and IPv6 (similar to OSPF for IPv6), which saves a lot of overhead.  IPv6 
>addresses are advertised in separate messages, which can be sent less 
>frequently.

And OSPF is different? OSPF uses a 32 bit router ID as well, and in OSPF V3 
always advertises prefixes in separate LSAs.

You are running into the same error we made in OSPF V2 regarding unnumbered 
links. In a number of cases, it is possible to come up with more than one 
way to get to a specified neighbor (maybe you have two radios and can talk 
with him via either) and it is important for operational reasons which 
route you take. If you can't identify them easily, you can't do this. So it 
is not sufficient to say "I have two routes to this neighbor", you have to 
be able to identify them.

OSPF V3 uses the link local address for that purpose.