WinNT: Connection Reset by Peer

1. External error: 

Check the hardware configuration of the network cards and the network components that are included. In specific, ensure that the full and half duplex settings are steady.
Check the hardware, generate and assess a network trace at the same time from the server and front end.
Use the "niping" tool to run a continuous test in order to test the network. In order to do this, start "niping" in the server mode on the R/3 server with the following command line from a command 
prompt: 

niping -s -I t=0
Then start "niping" in client mode on the frontend PC: 
niping -c -H -L 3600 -D 1000

Post this command, a packet of IKB is sent to the niping server every second and is received again. The test is repeatedly done for 3,600 times (approx. 1 hour). A disruption can be taken as a symbol of a network problem. The successful completion of this gives the minimum, maximum and average runtime of a package. In case, the minimum and average runtime is much lesser than the maximum runtime, this can indicate problems in the network. 

2. Windows NT uses PMTU discovery. Due to this reason, during connection setup, the TCP maximum segment size (MSS) for both partners is exchanged. The lower MSS value is ideally used for the connection. The 'don't fragment' is the flag which is set by default under Windows NT frames in the IP header. This 'don't fragment' flag inhibits fragmentation of the frames. When operating using a connection via a WAN network, the Maximum Transmission Unit (MTU) of a router or another unit within the connection link may vary from the MTU of the two end systems. If the size of a frame sent surpasses the MTU of a router, the TCP/IP stack of the sending system is expected to receive an ICMP message 'destination unreachable' as a reply. Most routers attach the relevant MTU for the next hop of this ICMP message. The host sends the frames again with the MTU that is and if no MTU is received by the ICMP message, a lower one is sent for the previous attempt. 

The connection is disturbed if the router does not answer with an ICMP message and rejects the frame. These routers are named as "Black Hole” routers. To check whether this problem is present, one should perform a text using the "niping" tool. Start niping on the R/3 server in server mode with the below given command line from a command prompt: 

niping -s -I t=0

After this start "niping" in client mode on the front end PC: 

niping -c - H -B 5000 -L 1000

After this command, 1000 packages of 5KB will be sent to the niping server and will be received again. This test should cause an interruption. One must repeat this test with a smaller buffer size: 

niping -c -H < R/3 hostname> -B 500 -L 1000 

As a result of this command, 1000 packages of 500 bytes will be sent and received back. This test must be successfully completed. In case a problem is noticed with a "Black Hole" router, there are two ways by which any issues can be avoided: 

a) Release the PMTU Black Hole Detection with the Registry Editor. As a result, the 'don't fragment' flag will no longer be set. The router can fragment frames and frames within the LAN will continue to send with the maximum MTU.

Windows NT, Windows 2000:

HKEY_LOCAL_MACHINESystemCurrentControlSetServicesTCPIPParameters
Through the Edit menu, insert - Add Value 'EnablePMTUBHDetect' with the data type 'REG_DWORD' and set the value to '1'. To release 'don't fragment', the value is reset to '0'. If parameter ‘EnablePMTUBHDetect' is not present by default then it must be added. 

Important: The parameter 'EnablePMTUBHDetect' can be activated only after a restart. 

Please note that the changes in the registry must be performed by a system administrator as improper changes made by an ignorant user can result in an operating system crash. 

b) Use the Registry Editor to decrease the MTU size (Maximum Transmission Unit). In this case, the size of the MTU corresponds to the smallest MTU of the network link. This value can be applied for communication within the LAN. This can cause degraded performance.
Windows NT: HKEY_LOCAL_MACHINESystemCurrentControlSetServicesTCPIPParameters
Windows 2000:
HKEY_LOCAL_MACHINESystemCurrentControlSetServicesTCPIPParameters
InterfacesID for Adapter
To insert 'MTU', use the Edit menu with the 'REG_DWORD' data type and set the value for the MTU. Ensure that the entry is in decimal form. Always choose a value that is lesser than the standard value. One can determine the size by using the "niping" tool. 
If the 'MTU' parameter is not present as default then it must be entered. 
Important: The 'MTU' parameter can be activated only after a restart. 

Default MTU values: 

Network MTU (bytes) ---------------------------------
16 Mbit/sec token ring 17914
4 Mbit/sec token ring 4464
FDDI 4352
Ethernet 1500
IEEE 802.3/802.2 1492
X.25 576
RESET N1
RESET N2