MTU // MSS using ASTF/IPv6

[Andreas Bourges]

Hi,

...we came across a little problem where we used the emix profile for IPv6 Tests. TRex replaces the IPv4 header using IPv6 header (+ 20bytes) and thus, increases the total packet length. In scenarios where the DUT has a MTU of 1500 this leads to problems with 1500-bytes packets, since the generated packets are of size 1520/1538.

Of course this is expected, but we did not think of this (until we discovered problems during our tests).

Would be good to have a hint in the docs pointing to this potential problem. Additionally the default MSS for IPv6 could be adjusted to 1440 for IPv6 (instead of default 1460, which is fine for IPv4).

Just to make sure - there's currently no mtu setting in TRex that would allow to limit the packet-size being sent on the wire (and bail-out in case of larger packets trying to sent...) - is there?

Thanks,

Andreas

[hanoh haim]

Hi Andreas, 

You are correct. There is no warning in case TRex packet size is bigger than the configured tunable MTU. 

It would be easy to report this error using a new counter. Do you think it better to drop the packet (tx) in such case?

thanks,

Hanoh 

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Hanoh

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[andyb...@googlemail.com]

Hi Hanoch,

 

…from my perspective – in a testcase-scenario it would be best to not start the test at all?! I wouldn’t want to generate packets larger than the locals system interface MTU. The only thing that could be interesting is the behavior of a DUT that receives packets larger than its MTU – but that’s achievable by setting trex MTU (however this can be done 😉) bigger than DUT MTU.

 

BTW – you mentioned “tunable MTU” – I didn’t find anything in the docs on setting the MTU of TRex interfaces 😉 ?

 

Thanks,

 

Andreas

 

 

Von: hanoh haim <hhaim...@gmail.com>
Gesendet: Dienstag, 3. Juli 2018 12:47
An: Andreas Bourges <andyb...@googlemail.com>
Cc: TRex Traffic Generator <trex...@googlegroups.com>
Betreff: Re: [trex-tgn] MTU // MSS using ASTF/IPv6

 

Hi Andreas, 

You are correct. There is no warning in case TRex packet size is bigger than the configured tunable MTU. 

It would be easy to report this error using a new counter. Do you think it better to drop the packet (tx) in such case?

 

thanks,

Hanoh 

 

On Tue, Jul 3, 2018 at 11:23 AM, 'Andreas Bourges' via TRex Traffic Generator <trex...@googlegroups.com> wrote:

Hi,

...we came across a little problem where we used the emix profile for IPv6 Tests. TRex replaces the IPv4 header using IPv6 header (+ 20bytes) and thus, increases the total packet length. In scenarios where the DUT has a MTU of 1500 this leads to problems with 1500-bytes packets, since the generated packets are of size 1520/1538.

Of course this is expected, but we did not think of this (until we discovered problems during our tests).

Would be good to have a hint in the docs pointing to this potential problem. Additionally the default MSS for IPv6 could be adjusted to 1440 for IPv6 (instead of default 1460, which is fine for IPv4).

Just to make sure - there's currently no mtu setting in TRex that would allow to limit the packet-size being sent on the wire (and bail-out in case of larger packets trying to sent...) - is there?


Thanks,

Andreas

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[hanoh haim]

Hi,

For TCP it is "tcp.mss" and for UDP there is no such tunable (we should add)

thanks,

Hanoh

 

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Hanoh

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