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When a Windows XP SP3 machine suddenly stops establishing new TCP connections while existing ones continue working, we're facing a classic resource allocation issue. The error message "no buffer space available" points to either:

• Exhausted non-paged pool memory
• TCP/IP stack resource leaks
• Driver memory management issues

@echo off
REM Check current TCP/IP parameters
netsh int ipv4 show dynamicport tcp
netsh int ipv4 show global
netsh int ipv4 show tcpstats

REM Check memory usage
poolmon.exe -b

Create a .reg file with these essential parameters:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"MaxFreeTcbs"=dword:00007d00
"MaxHashTableSize"=dword:00008000
"TcpTimedWaitDelay"=dword:0000001e
"NumTcbTablePartitions"=dword:00000004

For persistent issues, try resetting the TCP/IP stack:

netsh int ipv4 reset
netsh winsock reset

Then examine driver memory usage with:

driverquery /v /fo csv | findstr /i "nonpaged"

Create a scheduled task to periodically check resources:

schtasks /create /tn "TCP Resource Check" /tr "poolmon.exe -b > C:\logs\poolmon_%date%.log" /sc hourly /mo 6

This quirky behavior often manifests after prolonged uptime on Windows XP SP3 systems where:

New TCP connections fail with "no buffer space available" in PuTTY
Established connections (like mapped drives) continue working
DNS resolution and ICMP remain functional
Netstat shows normal connection counts



The issue stems from Windows XP's limited non-paged pool memory (typically 256MB max). When exhausted:
:: Check current non-paged pool usage
C:\>driverquery /v | find "Nonpaged"

Common memory hogs include:

Network interface drivers (especially Broadcom)
Antivirus software with network filtering
Legacy applications with memory leaks

Try these commands to temporarily alleviate symptoms:
netsh int ip reset reset.log
netsh winsock reset

For persistent cases, modify registry values:
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"MaxUserPort"=dword:0000fffe
"TcpTimedWaitDelay"=dword:0000001e

For critical production systems:

Patch TCPIP.SYS: Modify connection limits (use at your own risk)
; Example HEX edit for TCPIP.SYS (v5.1.2600.5512)
; Change 10 00 00 00 to FE FF 00 00 at offset 0x130

Hardware upgrade: Add physical RAM (if motherboard supports >4GB)
OS migration: Consider Windows Embedded POSReady 2009 (extended support)

Create a watchdog VBS script to detect early signs:
Set objWMIService = GetObject("winmgmts:\\.\root\cimv2")
Set colItems = objWMIService.ExecQuery("Select * From Win32_PerfRawData_PerfOS_Memory")

For Each objItem in colItems
    If objItem.PoolNonpagedBytes > 200000000 Then
        CreateObject("WScript.Shell").Run "netsh interface reset all"
    End If
Next