Auto MTU 1456

[xamp_np]

Hello,

i set my MTU up to 1484, but if i analyze my TCP/IP on this site, i see that my MTU nevertheless is 1456. Now I do not know what to do and I hope that someone can help me.


Some Informations:

Router-firewall is disabled
Router: Netgear mr 814v2
Provider: Tiscali
Broadband: 1mbit + fastpath
Network card : Realtek RTL8139-Familie-PCI-Fast Ethernet-NIC
System: Windows XP Professionel


Best regards
xamp_np

[trogers]

What broadband system are you using? Cable, PPPoA or PPPoE?

Post your TCP Analyzer and tell us what speed you are paying your ISP to give you.

[xamp_np]

Hi,

Internetport:
DHCP=PPPoE

With TTL it is the same. I set it on 64.


My results:

« SpeedGuide.net TCP Analyzer Results »
Tested on: 01.20.2007 08:24
IP address: 83.129.xxx.xxx

TCP options string: 02040588010303000101080a000000000000000001010402
MSS: 1416
MTU: 1456
TCP Window: 34848 (NOT multiple of MSS)
RWIN Scaling: 0
Unscaled RWIN : 34848
Reccomended RWINs: 65136, 130272, 260544, 521088
BDP limit (200ms): 1394kbps (174KBytes/s)
BDP limit (500ms): 558kbps (70KBytes/s)
MTU Discovery: OFF
TTL: 54
Timestamps: ON
SACKs: ON
IP ToS: 00000000 (0)

[trogers]

These settings are not for optimization. It is to try to first increase your MTU. Do the following with TCP Optimizer. After reboot, post a new TCP Analyzer report::

General Settings tab:
Custom settings - check
Modify All Network Adapters - check
network adapter selection - your NIC
MTU - 1500
TTL - 64
TCP Receive Window - leave blank
MTU Discovery - Yes
Black Hole Detect - No
Selective Acks - Yes
Max Duplicate ACKs - 2
TCP 1323 Options:
Windows Scaling - uncheck
Timestamps - uncheck

Advanced Settings tab:
Max Connections per Server - 10
Max Connections per 1.0 Server - 20
LocalPriority - 1
Host Priority - 1
DNSPriority - 1
NetbtPriority - 1
Lan Browsing speedup - optimized
QoS: NonBestEffortLimit - 0
ToS: DisableUserTOSSetting - 0
ToS: DefaultTOSValue - 80
MaxNegativeCacheTtl - 0
NetFailureCacheTime - 0
NegativeSOACache Time - 0
LAN Request Buffer Size - 32768
Then select "Apply Changes" and reboot to take effect

[xamp_np]

nothing happens, when i do that.


« SpeedGuide.net TCP Analyzer Results »
Tested on: 01.20.2007 11:28
IP address: 213.54.xxx.xxx

TCP options string: 0204058801010402
MSS: 1416
MTU: 1456
TCP Window: 34848 (NOT multiple of MSS)
RWIN Scaling: 0
Unscaled RWIN : 34848
Reccomended RWINs: 65136, 130272, 260544, 521088
BDP limit (200ms): 1394kbps (174KBytes/s)
BDP limit (500ms): 558kbps (70KBytes/s)
MTU Discovery: OFF
TTL: 54
Timestamps: OFF
SACKs: ON
IP ToS: 00000000 (0)

[trogers]

Use the TCP Optimizer and click 'File' and select Default Windows setting. Reboot comp and post TCP Analyzer report.

[xamp_np]

TCP options string = 02040588
MTU = 1456
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput. If you are using a router, it could be limiting your MTU regardless of Registry settings.
MSS = 1416
Maximum useful data in each packet = 1416, which equals MSS.
Default TCP Receive Window (RWIN) = 65535
RWIN Scaling (RFC1323) = 0 bits
Unscaled TCP Receive Window = 65535

Note: TCP 1323 Options need to be enabled for RWIN over 2^16 (65535). Windows 9x might also need the MS Vtcp386 fix.
For optimum performance, consider changing RWIN to a multiple of MSS.
Other RWIN values that might work well with your current MTU/MSS:
521088 (MSS x 46 * scale factor of 8)
260544 (MSS x 46 * scale factor of 4)
130272 (MSS x 46 * scale factor of 2)
65136 (MSS x 46)
bandwidth * delay product (Note this is not a speed test):

Your TCP Window limits you to: 2621 kbps (328 KBytes/s) @ 200ms
Your TCP Window limits you to: 1049 kbps (131 KBytes/s) @ 500ms
MTU Discovery (RFC1191) = OFF
Time to live left = 118 hops
TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = OFF
IP type of service field (RFC1349) = 00000000 (0)

[trogers]

Use the following with TCP Optimizer:

General Settings tab:
Custom settings - check
Modify All Network Adapters - check
network adapter selection - your NIC
MTU - 1456
TTL - 64
TCP Receive Window - 42480
MTU Discovery - Yes
Black Hole Detect - No
Selective Acks - Yes
Max Duplicate ACKs - 2
TCP 1323 Options:
Windows Scaling - uncheck
Timestamps - uncheck

Advanced Settings tab:
Max Connections per Server - 10
Max Connections per 1.0 Server - 20
LocalPriority - 1
Host Priority - 1
DNSPriority - 1
NetbtPriority - 1
Lan Browsing speedup - optimized
QoS: NonBestEffortLimit - 0
ToS: DisableUserTOSSetting - 0
ToS: DefaultTOSValue - 80
MaxNegativeCacheTtl - 0
NetFailureCacheTime - 0
NegativeSOACache Time - 0
LAN Request Buffer Size - 32768
Then select "Apply Changes" and reboot to take effect

After reboot, test your speed at this link using the recommended test server:

http://www.speedtest.net/

[xamp_np]

But i wanna know why I cannot use MTU 1484 ^^ It must give a reason for it

[trogers]

But i wanna know why I cannot use MTU 1484 ^^ It must give a reason for it

The normal MTU for PPPoE are 1492 and 1480. Some USB modems limit MTU to 1484. If you are lower than 1484, It may mean either the MTU (or MRU) setting in your modem is lower or that your ISP is limitng MTU.