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

["Sina Mirtorabi" <[e-mail]>]

Hi Vishwas 

->-----Original Message-----
->From: Vishwas Manral [mailto:[e-mail]] 
->Sent: Thursday, January 24, 2008 11:28 AM
->To: Acee Lindem
->Cc: OSPF List
->Subject: [OSPF] Re: draft-acee-ospf-multi-instance-00
->
->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.

The instance 0 is simply a reserved instance to interact with legacy
routers. Note that the reception of the OSPF packet with instance ID
field set to 0, cannot (and need not) imply if the remote router is /
'is not' Instance capable. If such a capability discovery is a
requirement, the Instance ID can be carried in Hello using LLS..

Thanks
Sina

->
->I understand what you mean - but would using LLS (which is 
->now a part of standards track now) be of any more help?
->
->Thanks again,
->Vishwas
->
->On Jan 24, 2008 10:56 AM, Acee Lindem <[e-mail]> 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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