foundry27 : Post

Forum Topic - io-pkt MTU size: (6 Items)

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Santhosh A(deleted)

06/27/2014 8:14 AM

post110878

Is there anyway to modify the MTU size in the io-pkt stack?  If yes, please let me know where and all I need to do the 
same?

I have requirement to add few bytes before the ethernet header, this is done in if_bridge.c file.  So along with this 
addition the packet length should not cross what is configured in the stack for ethernet transmission.  So i prefer to 
block the same in io-pkt such that TCP socket fragmentation will not cross the configured packet limit.

Please guide me in this.

Nick Reilly

06/27/2014 9:14 AM

post110880

Re: io-pkt MTU size

Each interface has its own MTU. It is configurable with ifconfig e.g. "ifconfig en0 mtu 1488".

Santhosh A(deleted)

06/29/2014 2:52 AM

post110886

Re: io-pkt MTU size

Thanks for the response.  Please guide me on the folllowing.

Is there anyway to change the following parameters of the stack?
•MTU being used by IP 
•MSS being used by TCP

Santhosh A(deleted)

06/29/2014 2:53 AM

post110887

Re: io-pkt MTU size

We do have licensed source code of io-pkt, so i am looking for places where these parameters are hard coded in the stack
.  Please guide me.

Nick Reilly

07/02/2014 2:43 PM

post110913

Re: io-pkt MTU size

MSS is negotiated by the two endpoints of the TCP connection with both of them advertising a value and the lowest value 
being used. The value to advertise is calculated from the MTU in io-pkt/sys/netinet/tcp_subr.c in the function 
tcp_mss_to_advertise().

The MTU is set by each driver when they call the technology specific attach function. For the standard Ethernet case 
this is ether_ifattach() in io-pkt/sys/net/if_ethersubr.c which sets the ifp->if_mtu to ETHERMTU. This ETHERMTU is 
defined in net/if_ether.h

Santhosh A(deleted)

07/11/2014 6:30 AM

post111030

Re: io-pkt MTU size

Thanks for the response.

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