Re: multihomed host

[Yoshihiro Ohba <yohba@tari.toshiba.com>]

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Thanks Iljitsch for detailed answer and Michel for the pointer.

Actually, I'm working in the PANA WG and viewing this kind of
multihomed host scenario from network access authentication
perspective, and wondering whether the PANA WG needs to consider this
scenario for now.  (My impression is that there is a lot of work to
consider before considering network access authentication)

Yoshihiro Ohba


On Thu, Oct 10, 2002 at 09:02:34AM +0200, Iljitsch van Beijnum wrote:
> On Wed, 9 Oct 2002, Yoshihiro Ohba wrote:
> 
> > > This is possible as of today; a host that has multiple PA addresses is
> > > certainly considered a multihomed host. However, this alone is not a
> > > multihoming solution.
> 
> > What additional things need to be considered for this usage to become
> > a multihoming solution?
> 
> A good multihoming solution keeps working if there are failures. So the
> applications must be smart enough to try all the addresses rather than
> just one. Telnet and FTP do this, WWW clients typically don't.
> Unfortunately, this must be done at the remote end and not on the
> multi(homed|addressed) host itself.
> 
> When there is a session, and the path over one ISP becomes unavailable,
> the multihomed host must switch to the path over the other ISP. There are
> many problems with this. First of all, the failure must be detected. Then
> the host can reroute outgoing packets. But if the host still uses the same
> source address (from the address space from the failed ISP), it is likely
> the packets won't be accepted by the alternate ISP because the source
> addresses are "spoofed". And even if they are, the communications partner
> keeps sending packets back to th source address tied to the first ISP,
> which isn't reachable any more.
> 
> One solution for the address problem would be the adoption of new or
> improved transport protocols that can handle this. There have been
> experiments with modifications to TCP to support this, and the new SCTP
> protocol can also handle this. However, modifying all transport protocols
> might be problematic.
> 
> Another solution is tunnelling/aliasing the packet to hide the original
> address while the packet is rerouted over the alternative path. The
> destination host or a box very close to the destination host strips of the
> tunnel header or replaces the original address so TCP and other transport
> protocols don't see the change in address.
> 
> Some of us are working on this stuff on a non-IETF mailinglist. The latest
> idea is to come up with a common tunnelling/aliasing framework so
> different solutions in this area may interoperate.
> 
> 

On Wed, Oct 09, 2002 at 11:11:09PM -0700, Michel Py wrote:
> >>> Yoshihiro Ohba wrote:
> >>> There may be some scenario in which a single-interface
> >>> host is connected to multiple ISPs on the same link, which
> >>> seems to be not covered in the usual definition for
> >>> "multihomed host". I don't know what to call the model,
> >>> but is such a model already common? Or is there any
> >>> ongoing work on this model?
>  
> >> Michel Py wrote:
> >> This is possible as of today; a host that has multiple PA
> >> addresses is certainly considered a multihomed host.
> >> However, this alone is not a multihoming solution.
> 
> > What additional things need to be considered for this
> > usage to become a multihoming solution?
> 
> There is no simple answer to this question. Here is one approach:
> http://arneill-py.sacramento.ca.us/ipv6mh/draft-bagnulo-mhExtHdr-00.txt
> 
> Michel.
> 
>