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Thread ID: 86445	2008-01-17 02:39:00	Website timeout issues with D-Link DSL504G router	marke (457)	Press F1

Post ID	Timestamp	Content	User
631165	2008-01-17 02:39:00	Hi all, I thought this might be useful for anyone looking to troubleshoot a similar problem. We recently setup an ADSL account with Maxnet, and used an inherited ADSL router from D-Link - a DSL-504G model to be precise. There are lots of these about as they are a model chosen by Telecom to be distributed as part of a "package deal" for Xtra broadband packages. What was happening was that on certain (AJAX-enabled) sites, we were experiencing page timeouts. We could access those sites fine on other internet connections. All machines on this connection experienced the same faults on those sites. So we started with Maxnet support (who were very helpful). They tested the same sites from their end and found those sites worked fine. Which indicated something to do with the router we were using. So I rang D-Link's technical support line. They told me that the issue was likely due to the MTU (Maximum Transmission Unit size) settings on my machine. This is a setting that controls the size of TCP packets sent through the network interface (card). The reason for this appears (I did some research) to be if the packet size setting is incorrect (i.e too big), packets have to be fragmented and re-assembled when they reach the router. And obviously in this case, that was causing a problem. So I downloaded a tool called TCPOptimizer from this site: www.speedguide.net Using TCPOptimizer , I changed the MTU settings on my PC to 1200, and retried the site that was causing the most problems. It worked perfectly. I then changed my MTU settings back to the default, and using the Router's configuration utility, set the MRU (Maximum Receive Unit size) setting on the router to 1454. I chose that figure because (according to this article : www.mynetwatchman.com) it seems to be the optimum packet size for a PPPoA broadband connection. I rebooted the router, and everything worked perfectly. My understanding (from Googling) is that windows machines by default are set to "auto-discover" the size of the packets they should send by interrogating the router. The router's MRU setting should tell the Windows tcpip stack not to send packets bigger than whatever the setting is. By default, the D-Link DSL-504G router has its MRU set to 1500. So windows dutifully sends packets up to 1500 in size ... which is too big for PPPoA connections (PPP over ATM - which is what DSL in NZ is) and causes packet fragmentation. In most cases the packets are fragmented and re-assembled OK .. but in the case of these particular sites we were using, it was causing issues. I've heard it has caused issues with banking sites (such as ANZ's banking site) on these Routers too. So - if you are getting weird problems like this, try reducing the size of your Router's MRU size and see if it fixes the problem. It's better to do that on the router, as setting the MTU on your local machine will mean that your network card will ALWAYS send packets of that size ... which might not be the optimum size for sending packets across your LAN network. Hope that's useful to someone??!! It caused me so much hair-pulling, that I thought it worthwhile to post it here ... Cheers Mark	marke (457)
631166	2008-01-17 02:52:00	Thanks for that - always good to have more tools :thumbs:	wainuitech (129)
631167	2008-01-17 03:58:00	Normally all you need to adjust is the router MTU settings which are 1500 by default usually. Setting to 1492 sometimes works better. I see you are referring to router MRU settings, never had to adjust that. You sure you are not getting MRU and MTU mixed up.	Safari (3993)
631168	2008-01-17 09:27:00	Normally all you need to adjust is the router MTU settings which are 1500 by default usually. Setting to 1492 sometimes works better. I see you are referring to router MRU settings, never had to adjust that. You sure you are not getting MRU and MTU mixed up. There are separate settings for MTU and MRU in the router. What is the story there?	rumpty (2863)
631169	2008-01-17 21:15:00	There are separate settings for MTU and MRU in the router. What is the story there? MRU="Maximum Receive Unit", MTU="Maximum Transmit Unit". Network interface = a network card in a PC, a router's ethernet port etc. My understanding (and I'm an IT guy but not a networking guru) is this: The MRU setting is what a network interface "advertises" to anything connecting to it (i.e other network interfaces) as the maximum packet size it can receive without fragmenting and re-assembling packets. The MTU setting sets the maximum packet size that an ethernet interface should ever send. So let's look at an example. If my machine's ethernet card has no MTU set, it will interrogate the network interface of the router/gateway or ethernet interface that it is sending traffic to, and ask it what maximum packet size it should send is. It will then send packets of that size. Suppose my router's MRU is set to 1492. My PC's ethernet card will get that advertised MRU from the router and send packets of 1492. However, if I alter my ethernet card's MTU setting to 1200 (leaving my router's MRU at 1492) my ethernet card will send packets of 1200 regardless of the MRU setting. So for most efficient setup, my understanding is that it's better to leave your ethernet card's MTU set to automatic. That way it should pick the optimum packet size from whatever network interface it's sending to. When sending packets to a server that might be 1500, and when sending to your ADSL router that might be 1492 (or 1454 - if you believe the article in the first post which suggests that is the optimum size for PPPoA ADSL connections). Now .. back to your question. The MRU setting on your router is what is the largest packet size its ethernet port can receive without fragmentation. Having received a packet, the MTU setting controls how big the packet that the router sends on should be. I'd suggest that both the MRU and MTU should probably be set to the same ... and either 1492 (the default setting on most routers for ADSL) or 1454 (based on that article). IP networking has several "layers". At the bottom-most layer there's the physical requirements of the type of network that the IP traffic is travelling over. Different physical layers have different requirements for the information in the packet - and therefore different "optimum" packet sizes. Sending a packet larger than the physical layer requires means that you're sending packets with unnecessary "empty" space in them - which is wasteful. Sending packets that are too small means that more packets need to be sent - also wasteful. Hope that is a) correct (any network gurus out there?) and b) clarifies how things work. It's a layman's explanation ... ;-) Cheers Mark	marke (457)
631170	2008-01-17 22:19:00	For a PPPOA connection the MTU does not matter that much. For PPPOE, which the article pointed to in the original post the MTU can make a difference as the PPP packets are encapsulated in Ethernet frames over the ATM frame. For PPPOA no additional encapsulation is occurring, but the cell math still applies. Some cheap low quality routers can benefit from a lower MTU as they cannot keep up with high volume traffic or re-assemble fragmented packets quick enough. Also some brain dead website IT people seem to set the do not fragment bit on all their traffic, why I have no idea, and that causes problems all through the up-stream path. In this situation you should complain to the webmaster and their provider! Also only Server 2003 / Vista or better will by default do auto MTU discovery for the others you must manually enable it.	ughnz (8297)
631171	2008-01-18 01:47:00	Thanks, guys, interesting discussion.	linw (53)
631172	2008-02-19 06:14:00	Thanks for posting this, Marke - it's really helped me out! I'm going to add my similar experience in case it helps anyone else, too: I've just registered with Xnet ADSL broadband here in NZ, and had a similar problem. Certain websites would not load at all on broadband (but had no problems when using dial-up). The websites which failed to load were quite random. For instance, stuff.co.nz and dunbarsloane.co.nz wouldn't load, whereas google.co.nz and trademe.co.nz were both fine. The websites which failed could still be accessed via proxy servers. I am running Vista Business (32-bit) on a Samsung Q35 notebook and am using a wireless Actiontec DSL Gateway (GT701-WG). I implemented all the set-up instructions on the Xnet website (www.xnet.co.nz). I tried updating the firmware on the DSL gateway, but this didn't solve the problem. There are no MTU settings options on the Actiontec DSL Gateway itself. Finally, I used these instructions from another forum (www.neowin.net) to change the MTU in Vista: 1. Open a command prompt as an administrator (type "cmd" in the Start Search dialogue, right-click on the "cmd" application which comes up and select "Run as administrator") 2. Make sure that you are in the "C:\Windows\System32" directory 3. Type the following to view your current MTU settings: netsh interface ipv4 show subinterfaces In my case, the output was as follows: MTU MediaSenseState Bytes In Bytes Out Interface ------ --------------- --------- --------- ------------- 4294967295 1 0 6796 Loopback Pseudo-Interface 1 1500 1 2910258 760573 Wireless Network Connection 1500 5 0 0 Local Area Connection 4. Change the MTU by typing: netsh interface ipv4 set subinterface "Wireless Network Connection" mtu=1454 store=persistent (if you are using a Local Area Connection, or your interfaces have other names, you will need to change this in the string above) It should then say "Ok." [NB: if you get the message "The requested operation requires elevation" then you haven't run the cmd window as an administrator - you need to close and restart cmd by clicking 'Run as administrator' on the right-click menu] 5. Check that the change has been made by repeating step 3. This time you should get something like: MTU MediaSenseState Bytes In Bytes Out Interface ------ --------------- --------- --------- ------------- 4294967295 1 0 6796 Loopback Pseudo-Interface 1 1454 1 3021011 847314 Wireless Network Connection 1500 5 0 0 Local Area Connection 6. Restart your computer, then try the problematic websites and see if your problem is solved - worked a treat for me! I don't know yet what the optimum MTU setting is - I'm just excited to have working broadband at all! As an aside, I telephoned Xnet customer support when I first had this website access problem - I knew there must be some sort of issue with the router settings, but the support guy just kept saying that the problem was the websites themselves refusing my IP address. He suggested I contact each of the websites which didn't work, tell them my IP address and ask them to allow connections from that IP address. :illogical I didn't do this, of course - I just told him I'd sort out the problem myself.	drbob (13292)
631173	2008-07-25 01:14:00	Ok noticed this, so signed up for the forum. In N.Z on PPPoA (not Telstra cable in Wlly and Chch) use MTU 1400, MRU 1492. Some users may try 1300 for there MTU with Microsoft sites, as these highly depend on AJAX servers and coding. If using Woosh or Cable and a PPPoE dialler is used or not, try 1500 for MTU where possible. If you have a modem or option to change the MSS, this is always minus 40 of your MTU. So if MTU = 1400, MSS 1360 or MTU = 1500, MSS = 1460.	netmatrix (13293)
631174	2008-07-25 01:25:00	Additionally two sites for further info. http://www.speedtest.net - Speed test your connection, in which should approx divided by 10 of your line speed. So if line sync rate is 7616 kbps. transfer rate (which your apps usually measure by) will equal to 761 KB/s maybe less depending on attenuation (loss over distance) and the distance/route from the server/client your contacting/getting/sending data to or from. speedguide.net:8080 (http:) - Shows your MTU and related settings. Geekish but nice.	netmatrix (13293)
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