6.2 mtu now limits size of incomming packet

[Stephen Clark]

Mike Karels wrote:

>>A related change that should probably be discussed if we want to think more 
>>about asymmetry in maximum transmission unit is this one:
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>>   revision 1.98
>>   date: 2006/06/26 17:54:53;  author: andre;  state: Exp;  lines: +2 -0
>>   In syncache_respond() do not reply with a MSS that is larger than what
>>   the peer announced to us but make it at least tcp_minmss in size.
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>>   Sponsored by:   TCP/IP Optimization Fundraise 2005
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>>In this change, we cap the advertised MSS in SYN/ACK to the received 
>>advertised MSS, which presumably avoids an extra PMTU round trip if jumbograms 
>>are enabled on the receiving endpoint.  However, it also prevents use of 
>>larger packet sizes if asymmetric MTU is supported.  I think I suggested after 
>>this was committed that we at least add an administrative twiddle to 
>>enable/disable this mode of operation, but don't see one in there currently. 
>>Does the Secure Computing scenario use TCP in this way, and is the potential 
>>win in avoiding a PMTU round-trip worth disallowing asymmetric MSS at the TCP 
>>layer?
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>In our case, TCP isn't aware of the MRU, and bases its MSS on the MTU values.
>However, I don't see any reason for TCP to cap the MSS at the received MSS.
>If the other end doesn't want to receive more than 1024 bytes, that's no
>reason to refuse to accept more.
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>		Mike
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So was any decision reached on this issue - will FreeBSD changed to 
accept a packet on an
interface that is larger than the mtu on that interface?

Steve

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