Router lowers DSL download speed

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Shedoni

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Apr 27, 2004
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After adding a Linksys WRT54G wireless router to my system in order to allow internet access to a second PC, download speeds have decreased almost to the point of a dial-up connection. When I remove the router, download speeds return to where they should be.

Broadband reports.com after speed test recommended "tweak test" but that test caused my computer to hang up. And I don't even know what "tweak" refers to anyhow so I'm afraid to go further without some advice.

I know this has to be a router problem, but, being a complete novice in the router department, I've no idea what to do about it. Anyone have suggestions?

My computer:
Windows 98SE
AMD Athlon1ghz
256 MB Ram
Modem: VisionNet ADSL 202ES
 

JohnWill

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Oct 19, 2002
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106,556
First off, in the router's WAN configuration page, try setting the MTU value to 1492 if it's not already set.
 

Shedoni

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John, I changed the MTU as you suggested (it was 1500--set auto) and dl speed increased a little---from 77 to 95 but without router, my download speed is about (acceptable) 430! I'd sure like to get dl router speed higher than 95 ( since DSL subscription is 768/256).
 
Joined
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894
Why 1492?

Is "Block WAN REQUESTS" checked on the router? If it is, please uncheck it.

Change your MTU back to 1500.

Do this: "ping -l 1472 -f www.nanog.org"

You should see something like this;
Pinging www.nanog.org [198.108.1.50] with 1472 bytes of data.
Reply from 198.108.1.50: bytes=1472 time=94ms TTL=243
Reply from 198.108.1.50: bytes=1472 time=120ms TTL=243

If you do, try downloading again. If speed is bad, try new Ethernet cables.

If you see "Packet needs to be fragmented but DF set." Lower the number by 16 until you achieve something that works. You can try setting the MTU on your Ethernet interface to this number, not a REAL solution, but it'll help.
 

JohnWill

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Well, depending on your specific ISP, perhaps even the 1492 isn't sufficient. You can experiment chopping it down 100 at a crack until you get to around 500 and see if there's a point where things go faster.
 
Joined
Aug 26, 2005
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Right.. All I'm saying is that 1492 is a completely arbitrary number.

Ethernet frame format:

* 6 byte dest addr
* 6 byte src addr
* [4 byte optional 802.1q VLAN Tag]
* 2 byte length/type
* 46-1500 byte data (payload)
* 4 byte CRC

Ethernet overhead bytes:
12 gap + 8 preamble + 14 header + 4 trailer = 38 bytes/packet w/o 802.1q
12 gap + 8 preamble + 18 header + 4 trailer = 42 bytes/packet with 802.1q

Ethernet Payload data rates are thus:
1500/(38+1500) = 97.5293 % w/o 802.1q tags
1500/(42+1500) = 97.2763 % with 802.1q tags

TCP over Ethernet:
Assuming no header compression (e.g. not PPP)
Add 20 IPv4 header or 40 IPv6 header (no options)
Add 20 TCP header
Add 12 bytes optional TCP timestamps
Max TCP Payload data rates over ethernet are thus:
(1500-40)/(38+1500) = 94.9285 % IPv4, minimal headers
(1500-52)/(38+1500) = 94.1482 % IPv4, TCP timestamps
(1500-52)/(42+1500) = 93.9040 % 802.1q, IPv4, TCP timestamps
(1500-60)/(38+1500) = 93.6281 % IPv6, minimal headers
(1500-72)/(38+1500) = 92.8479 % IPv6, TCP timestamps
(1500-72)/(42+1500) = 92.6070 % 802.1q, IPv6, ICP timestamps

UDP over Ethernet:
Add 20 IPv4 header or 40 IPv6 header (no options)
Add 8 UDP header
Max UDP Payload data rates over ethernet are thus:
(1500-28)/(38+1500) = 95.7087 % IPv4
(1500-28)/(42+1500) = 95.4604 % 802.1q, IPv4
(1500-48)/(38+1500) = 94.4083 % IPv6
(1500-48)/(42+1500) = 94.1634 % 802.1q, IPv6
 

JohnWill

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Actually, if you look around a bit, you'll find that 1492 is not really an arbitrary number. If you run PPPoE, it adds an additonal overhead of 8 to the packet, which accounts for the difference between the maximum of 1500 and 1492. I'm a bit surprised you didn't know that. :confused: Many times the default configuration for a router with PPPoE automatically sets the MTU to 1492 to account for that, but since his was at 1500...
 
Joined
Jan 2, 2006
Messages
98
First of,
Are you on wireless or wired connection from PC to router?
If its wireless then you might have interferance issue.
You need to determine if your connection is slowing down between router and PC or router and modem.
Try to ping your default gateway (your router).start-run-cmd-ipconfig
Type in ping {default gateway IP}
You should get 4ms TOPS.
Go to linksys and download newest firmware.
Linksys should work good right out of box so i would get on the phone with them and wouldn't let go untill i get resolution.
You can try to hard reset your router. There should be a place where you can stick a pin a hold it for 10sec or more. That will factory reset the router.

Hope it helps

220VOLT-INFORMATION TECHNOLOGY HIGHWAY
Your source for Networking, Computers, IT Exams, Free E-books and more..
 

Shedoni

Thread Starter
Joined
Apr 27, 2004
Messages
20
:eek:
Hey guys.....yikes.....remember? I am a novice when it comes to routers---and finding my way around configs, too, I guess.

I see no mention of "blocked WAN requests" anywhere in setup or config. When I try to follow suggestion to "ping" anything, I get a momentary screen than flashes and then disappears---certainly too fast to read. I see it's a dos program. Would it be better if I tried to "ping" (whatever that is---I see it used on forums, but don't know what it does--or is supposed to do--same goes for "tweak" as I mentioned). I can't see how new ethernet cable would help since I get good speeds connecting ethernet cable directly to dsl modem when I take the router offline.

I think I am getting way too many alternatives so I will have to try them one at a time in order to make sure I don't set up a conflict between them. But my head is spinning from all the different directions from all directions. And I don't begin to understand all the numbers, etc, posted by O111111O or what I should do with them.

John, going lower than 1492 did not help.
I am beginning to wonder if 220Volt is not correct about needing help from Linksys. This is a new router. And--it's also the only router--wireless or otherwise--that I've ever had. And, 220Volt, as I mentioned, this decrease in dl speed only occurs when I connect by way of the router by ethernet cable to one of four router ports with this PC. (The second PC is on wireless and also runs slow, but I haven't even been concerned with that until I get this main one working. If I move the ethernet cable directly to the DSL modem taking the router (and it's cable, of course) out of the string, the speed shoots up to where it belongs--but of course, that defeats the purpose of having the wireless router in the first place so the second (remote) PC is then without internet connection.

I will call the DSL/ISP service tomorrow and if they can't help, I will contact Linksys as 220Volt has suggested. Then I'll be back to report.

Thanks, all, for trying. I'll let you know if any of us are looking in the right direction.:eek:
 
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