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hknet
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MLPPP MTU testing...

Thu Mar 25, 2021 5:49 pm

Hi
we are experiencing some really strange MLPPP situations with RouterOS:
we set MRU = 1470 and MRRU=1500 we get an mlppp-interface-mtu=1480

we set the interface mtu for the ethernet-interfaces carrying the ppp-streams to MTU=1520
no special mtu/mru/mrru settings in mlppp-dialer we get a nominal MTU=1500 (good), but:
if we try to do a bandwidthtest we have to set the loclal udp size to 1498 to get it working fine.

suggestion from MT-support: mlppp takes 12-bytes-overhead, we should accomodate, ok,
we set the ethernet-mtu to 1522, we get a dialer MTU=1502, in the end we always get it
two byte wrong.

we set things to default (interface-mtu=1500, mlppp-dialer no settings), we get another
mlppp-interface-MTU at 1480, well what the heck, of course local udp size has to be
cecreased to 1478.

if we do these very same bandwidth tests on a single-pppoe-connection - everything is fine
the default values of the bandwidthtest work fine, as well as when we seht the local
udp-tx-size to 1480 - all is fine.

we first saw this phenomenon on a ccr2004 box (ROS 6.46.8, 6.47.9, 6.48.1),
but after some further probing I guess this is not a specific model but rather a
fundamental thing that is happening here (tested also on rb2011,3011).

we reached the point of total no clue.

could anybody enlighten us?

thx
hk
 
jkyawesome
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Re: MLPPP MTU testing...

Sun Mar 28, 2021 11:15 pm

Most tutorials recommend MRI to be set at 1600
 
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hknet
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Posts: 126
Joined: Sun Jul 17, 2016 6:05 pm
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Re: MLPPP MTU testing...

Wed Mar 31, 2021 12:45 am

Most tutorials recommend MRI to be set at 1600
MRI?

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