tipc: MTU discovery

tipc: MTU discovery

[Sebastian Pöhn]

I am trying to run TIPC over a link with a MTU higher than standard
1500 (actually 2k or more).

I have a Ethernet Device configured with this MTU and an overlying
VLAN with the same MTU. Link Layer looks ok, as MTU sized ICMP traffic
is sent and received unfragmented.

TIPC does not discover the higher MTU, it always keeps at 1500.
Smaller ones (1.4k) are detected correctly.

Doing some deeper investigation into the TIPC stack leaded to this observation:
State Messages larger than 1500 which as used for the MTU negotiation
do not appear in the TIPC stack. But I am able to seen them entering
the correct device.
Because of that no reply with the correct max_packet field set can be
send and the negotiation will always end up at 1.5k.

So my questions are:
# Is TIPC meant to detect and use the MTU larger than 1.5k?
# Why are the packets not passed to the TIPC stack?

Re: tipc: MTU discovery

[Erik Hugne]

On Tue, Mar 05, 2013 at 01:43:29PM +0100, Sebastian Pöhn wrote:
> State Messages larger than 1500 which as used for the MTU negotiation
> do not appear in the TIPC stack. But I am able to seen them entering
> the correct device.
> Because of that no reply with the correct max_packet field set can be
> send and the negotiation will always end up at 1.5k.
> 
> So my questions are:
> # Is TIPC meant to detect and use the MTU larger than 1.5k?
Yes, it should probe and detect MTU's up to ~66k

> # Why are the packets not passed to the TIPC stack?
TIPC just registers itself as a handler for ETH_P_TIPC through dev_add_pack.
If link mtu probes >1.5k are not passed to TIPC, it sounds to me that the NIC driver
is to blame. What NIC type and kernel version are you running?

Do you see any packet drops in ethtool statistics?

//E

Re: tipc: MTU discovery

[Sebastian Pöhn]

I run a DLink DGE-528T (PCI-ID: 1186:4300). Kernel is 2.6.32
There is a dedicated VLAN sitting over the physical device.

I even made some similar observations in a VM environment but I think
this is even a more fragile setup.

Will install ethtool ...

On Tue, Mar 5, 2013 at 3:18 PM, Erik Hugne <erik.hugne@ericsson.com> wrote:
> On Tue, Mar 05, 2013 at 01:43:29PM +0100, Sebastian Pöhn wrote:
>> State Messages larger than 1500 which as used for the MTU negotiation
>> do not appear in the TIPC stack. But I am able to seen them entering
>> the correct device.
>> Because of that no reply with the correct max_packet field set can be
>> send and the negotiation will always end up at 1.5k.
>>
>> So my questions are:
>> # Is TIPC meant to detect and use the MTU larger than 1.5k?
> Yes, it should probe and detect MTU's up to ~66k
>
>> # Why are the packets not passed to the TIPC stack?
> TIPC just registers itself as a handler for ETH_P_TIPC through
> dev_add_pack.
> If link mtu probes >1.5k are not passed to TIPC, it sounds to me that the
> NIC driver
> is to blame. What NIC type and kernel version are you running?
>
> Do you see any packet drops in ethtool statistics?
>
> //E

Re: tipc: MTU discovery

[Ying Xue]

1. Can you dump all TIPC packets for us while TIPC link is established?

2. There has a big gap between 2.6.32 and 3.8, meaning TIPC code is also
made big changes. If you can reproduce the problem on latest kernel
version, please let us know.

Thanks,
Ying

On 03/06/2013 12:22 AM, Sebastian Pöhn wrote:
> I run a DLink DGE-528T (PCI-ID: 1186:4300). Kernel is 2.6.32
> There is a dedicated VLAN sitting over the physical device.
> 
> I even made some similar observations in a VM environment but I think
> this is even a more fragile setup.
> 
> Will install ethtool ...
> 
> On Tue, Mar 5, 2013 at 3:18 PM, Erik Hugne <erik.hugne@ericsson.com> wrote:
>> On Tue, Mar 05, 2013 at 01:43:29PM +0100, Sebastian Pöhn wrote:
>>> State Messages larger than 1500 which as used for the MTU negotiation
>>> do not appear in the TIPC stack. But I am able to seen them entering
>>> the correct device.
>>> Because of that no reply with the correct max_packet field set can be
>>> send and the negotiation will always end up at 1.5k.
>>>
>>> So my questions are:
>>> # Is TIPC meant to detect and use the MTU larger than 1.5k?
>> Yes, it should probe and detect MTU's up to ~66k
>>
>>> # Why are the packets not passed to the TIPC stack?
>> TIPC just registers itself as a handler for ETH_P_TIPC through
>> dev_add_pack.
>> If link mtu probes >1.5k are not passed to TIPC, it sounds to me that the
>> NIC driver
>> is to blame. What NIC type and kernel version are you running?
>>
>> Do you see any packet drops in ethtool statistics?
>>
>> //E
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Re: tipc: MTU discovery

[Sebastian Pöhn]

It is actually cause by the NIC. It is dropping everything larger than
MTU 1500 on the RX side. But TX is working ...

So I'll gonna do it like always:
If the SW does not work, change the HW

Thanks for the hint

On Tue, Mar 5, 2013 at 3:18 PM, Erik Hugne <erik.hugne@ericsson.com> wrote:
> On Tue, Mar 05, 2013 at 01:43:29PM +0100, Sebastian Pöhn wrote:
>> State Messages larger than 1500 which as used for the MTU negotiation
>> do not appear in the TIPC stack. But I am able to seen them entering
>> the correct device.
>> Because of that no reply with the correct max_packet field set can be
>> send and the negotiation will always end up at 1.5k.
>>
>> So my questions are:
>> # Is TIPC meant to detect and use the MTU larger than 1.5k?
> Yes, it should probe and detect MTU's up to ~66k
>
>> # Why are the packets not passed to the TIPC stack?
> TIPC just registers itself as a handler for ETH_P_TIPC through dev_add_pack.
> If link mtu probes >1.5k are not passed to TIPC, it sounds to me that the NIC driver
> is to blame. What NIC type and kernel version are you running?
>
> Do you see any packet drops in ethtool statistics?
>
> //E