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[OSPF] Re: draft-acee-ospf-multi-instance-00

Hi Vishwas,

On Jan 24, 2008, at 2:28 PM, Vishwas Manral wrote:

Hi Acee,

Thanks a lot for the reply. The backward compatibility issue would
come unless there would be the case that the draft would not use
instance ID 0 (when working with a router not supporting the
functionality - where it would be treated as no instance - rather than
a particular instance). May be that could be clarified.

I understand what you mean - but would using LLS (which is now a part
of standards track now) be of any more help?

LLS is only for hello and DD packets. This is required for all OSPF packets. Also, I'd rather keep the solutions aligned with what we have today with OSPFv3. Furthermore, if there are implementations that gratuitously log authentication failures, there may be implementations that do the same for unrecognized LLS TLVs.

Thanks,
Acee


Thanks again,
Vishwas

On Jan 24, 2008 10:56 AM, Acee Lindem <acee at redback.com> wrote: 
 Hi Vishwas,

From a protocol standpoint, it is completely backward compatible. OSPF
routers not supporting the draft but receiving a multicast OSPF packet with
a non-zero instance ID will simply treat it as an unknown AuType and fail
authentication.

With this respect, RFC 2328 simply states:


 8.2.  Receiving protocol packets
                         o
                         o
                         o
 o   The packet must be authenticated.  The authentication
       procedure is indicated by the setting of AuType (see
       Appendix D).  The authentication procedure may use one or
       more Authentication keys, which can be configured on a per-
        interface basis.  The authentication procedure may also
        verify the checksum field in the OSPF packet header (which,
        when used, is set to the standard IP 16-bit one's complement
        checksum of the OSPF packet's contents after excluding the
        64-bit authentication field).  If the authentication
        procedure fails, the packet should be discarded.


And:


    D.5 Message verification

When an OSPF packet has been received on an interface, it must
be authenticated. The authentication procedure is indicated by
the setting of Autype in the standard OSPF packet header, which
matches the setting of Autype for the receiving OSPF interface.

If an OSPF protocol packet is accepted as authentic, processing
of the packet continues as specified in Section 8.2. Packets
which fail authentication are discarded.

Speaking as a draft author (not OSPF WG Co-chair):

Unfortunately, some well-deployed implementations make a bigger fuss than is
necessary when an authentication failure occurs. IMHO, now would be a good
time to rectify this to lesses the impact should this draft be accepted as a
standards track document. Of course, there are manual ways of segregating
the multi-access networks to avoid down-level routers from receiving
multicast packets for non-zero instances. Perhaps, we should discuss these
in the draft and dispense with the more radical discussions of requesting
new multicast addresses or other IANA code points.

Thanks,
Acee




On Jan 24, 2008, at 12:49 PM, Vishwas Manral wrote:

Hi Acee,

I wanted to know if this draft was backward compatible with current
implementation. If its not, I was also eager to know, if we have a way
for incremental deployment.

Thanks,
Vishwas



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