2008r2 Connections stuck in SYN_Received

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i have been pulling hair out on issue while , not getting anywhere.

i seeing issues whereby connections regularly getting stuck in syn_received main place manifesting port 80 see if on port 443. server 2008r2 running iis, mysql , ad (i know not ideal , should immediate redflag, customers server won't change not lot can in short term) manifesting sites being unavailable clients , our monitoring software picking site down socket error #10060.

windows firewall off

i have installed hotfix suggested here: https://support.microsoft.com/kb/2786464

i suspect syn protection kicking aggressively have no real way have found of tuning down (i suspect fact server dc making more aggressive) 

it has made difference not fixed problem yet.

"netsh interface tcp show global" returning:

querying active state...

tcp global parameters
----------------------------------------------
receive-side scaling state                : enabled 
chimney offload state                      : disabled 
netdma state                                  : enabled 
direct cache acess (dca)                 : disabled 
receive window auto-tuning level    : normal 
add-on congestion control provider  : ctcp 
ecn capability                                 : disabled 
rfc 1323 timestamps                      : disabled 
initial rto                                       : 3000 
non sack rtt resiliency                    : disabled 
max syn retransmissions                 : 4 

nic a broadcom bcm5716c netxtreme ii gige

any @ appreciated.


hi ade,

first, please run "netsate -an -p tcp" find remote ip address stuck in syn_received connection.

if few remote ip addresses initiate lot of half-open connections, server may under attack.

if ip address local, please check client. if ip address public, please consult isp or setup tmg prevent server syn attack.

if server not under attack, please check registry key below:

  • hkey_local_machine\system\currentcontrolset\services\tcpip\parameters


    value name: tcpmaxdataretransmissions
    data type: reg_dword - number
    valid range: 0 - 0xffffffff
    default: 5

    value name: initialrtt
    data type: reg_dword
    valid range: 0-65535 (decimal)
    default: 0xbb8 (3000 decimal)

if find synattackprotect key, , computer not under syn attack, delete key.

best regards.

steven lee please remember mark replies answers if , unmark them if provide no help. if have feedback technet support, contact tnmff@microsoft.com.




Windows Server  >  Windows Server General Forum



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