max MTU for fwip device.

[Doug Rabson]

On Tue, 2004-08-10 at 10:12, Alexander Nedotsukov wrote:
> Doug Rabson wrote:
> 
> >On Tuesday 10 August 2004 04:41, Alexander Nedotsukov wrote:
> >  
> >
> >>Doug Rabson wrote:
> >>    
> >>
> >>>On Monday 09 August 2004 04:06, Alexander Nedotsukov wrote:
> >>>      
> >>>
> >>>>Hi again,
> >>>>Is there any reason why we do not support MTUs higher than 1500
> >>>>bytes on firewire links?
> >>>>        
> >>>>
> >>>Basically, we are limited by the specification. The rfc states that
> >>>the default MTU should be 1500 bytes. From the spec: "NOTE:
> >>>IP-capable nodes may operate with an MTU size larger than the
> >>>default, but the means by which a larger MTU is configured are
> >>>beyond the scope of this document."
> >>>      
> >>>
> >>Well standards are good. But I don't see any restriction here. In
> >>fact I belive that effective MTU should be evaluated from maximum
> >>payload table (RFC2734 Table 1) and ieee1394 header size. Anyway this
> >>1500 which comes from 10Mbit ethernet land may be good for default
> >>but manual configuration should not be prohibited.
> >>
> >>Btw default MTU size on MacOSX for fw? interface is 2030 which is 10
> >>bytes less that theoretical maximum for S400 async stream.
> >>
> >>    
> >>
> >
> >Interesting. The specification for IPv6 on firewire is clearer:
> >
> >   The default MTU size for IPv6 packets on an IEEE1394 network is 1500
> >   octets.  This size may be reduced by a Router Advertisement [DISC]
> >   containing an MTU option which specifies a smaller MTU, or by manual
> >   configuration of each node.  If a Router Advertisement received on an
> >   IEEE1394 interface has an MTU option specifying an MTU larger than
> >   1500, or larger than a manually configured value, that MTU option may
> >   be logged to system management but MUST be otherwise ignored.  The
> >   mechanism to extend MTU size between particular two nodes is for
> >   further study.
> >  
> >
> Mmm. I still do not see any prohibition of MTU size > 1500. What I see 
> here is definition of automatic MTU adjustment. It's stated that ATM MTU 
> size may be only reduced by such mechanism. Am I right?
> So manual configuration of interface for MTU size > 1500 violates nothing.

Of course - I certainly don't want to stop people from configuring an
MTU size > 1500. I just think that for the compiled in default, we
should go with the spec for now.