max MTU for fwip device.

[Alexander Nedotsukov]

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.

All the best,
Alexander.