"Don't Fragment Bit" in data sent from SAP MI client

[Former Member]

Hi All,

Does anyone knows anything about a "Fragment Bit" which is set with sending data from SAP MI client to SAP WAS (middleware)?

The data is sent with a "Don't fragment bit" and one of our switches/routers or something in the network has to fragment our data, but the bit is set. So the MI client receives an error message (Unexpected end of file from server).

We want to set something in the SAP MI client which sais this datapacket may be fragmented so it can pass the network switches/routers/etc.

Can someone help us with this problem?

Thanks in advance and kind regards,

Bart Elshout

[Former Member]

hello bart,

is this something low level? i.e. setting a flag in the

packet?

regards

jo

[Former Member]

I don't know what is happening, but it looks like it is something in the MI framework which is setting the DF bit.

Can we overrule this setting or change it? Do you know enything about this?

Thanks, Bart Elshout

[Former Member]

MI doesn't deal on the packet level. Perhaps, you can try

checking on your network card configuration if there are

some properties which are related to this issue...

jo

[Former Member]

Hi Jo,

So you think MI is not setting the "Don't fragment bit" but our network card is setting it?

Or do you think the application running on MI is setting this bit?

We are running an application based on SAP MAM so it can be MAM is setting this bit, but I don't expect MAM is doing this. I expected MI framework was doing this.

Please correct me if you are 100% sure MI is not doing this.

Thanks in advance and kind regards,

Bart

[Former Member]

hello bart,

in my opinion, as long as there are no native addons

installed, im pretty confident that MI doesn't deal on

the network packet level...

jo

[Former Member]

Hi Jo,

I think it is a problem from client --> sync gateway. But how can I check?

If I sync I get the message "Unexpected end of file from server". As far as I can see this problem is occuring because there is a router/switch/bridge/etc. on the network which is trying to fragment my data, but in the data package the "Don't fragment bit" is set. So there is an error message send back to my client.

We figured this out with sniffering on the data which is sent from the client and to the client.

Do you understand what I mean?

Thanks,

Bart

[Former Member]

Hello Jo,

I will close my other thread, because we the other thread is just about the same problem.

Can we talk about this problem in this thread?

Thanks,

Bart

[Former Member]

hello bart,

can you point which layer (ISO or TCP/IP model) this

"Don't fragment bit" packet is?

regards

jo

[Former Member]

Hi Jo,

It think it should be at layer 2 of the OSI model.

Here is there <a href="http://www.mindforums.com/forums/showthread.php?s=1c939bf86b65ca2ee4e153e8cab898f1&threadid=324&goto=nextoldest">SOURCE</a>:

<i>"Even though the IP header has a "total packet length" of 65,535, (16 bits), it seems like actual IP datagrams are almost always designed to avoid fragmentation by layer 2, and to avoid fragmentation the tcp segment is designed to fit within an IP datagram."</i>

[Former Member]

hello bart,

MI only works for layer 7.

dont fragment bit is something related to MTU. it might

worth checking on the network card settings of your MI

sync gateway if the messages are fragmented from the

gateway server to the client.

check out <a href="http://support.microsoft.com/kb/314053">TCP/IP NBT parameters for WinXP</a>.

<i>EnablePMTUBHDetect

Key: Tcpip\Parameters

Value Type: REG_DWORD - Boolean

Valid Range: 0,1 (False, True)

Default: 0 (False)

Description: If you set this parameter to 1 (True), TCP

tries to detect "Black Hole" routers while doing Path MTU

Discovery. A "Black Hole" router does not return ICMP

Destination Unreachable messages when it must fragment an

IP datagram with the Don't Fragment bit set. TCP must

receive these messages to perform Path MTU Discovery.

With this feature enabled, TCP will try to send segments

without the Don't Fragment bit set if several

retransmissions of a segment are unacknowledged. If the

segment is acknowledged, the MSS will be decreased and

the Don't Fragment bit will be set in future packets on

the connection. Enabling black hole detection increases

the maximum number of retransmissions that are performed

for a particular segment. </i>

regards

jo

[Former Member]

Hi Jo,

I will do some other investigation, but thanks till so far.

We sniffered on the network card of the client and on the network card of the server. The networkteam is looking for a problem in the network/firewall.

I this is a death end I will respond again on this thread.

Thank you very much for your help.

Kind Regards,

Bart Elshout