Unable to access most web sites with new Linksys E4200 Router
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Re: Unable to access most web sites with new Linksys E4200 Router
04-05-2012 4:37 PM
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Disabling the FW did not have an effect.
Thanks
Re: Unable to access most web sites with new Linksys E4200 Router
04-05-2012 5:35 PM
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I suspect an MTU issue - judging by the capture file. I'm not 100% sure how to go about fixing this though. Possibly you need to log into the router and try finding an MTU value to change to something higher (1492/manual should work). Could you let us know what it is currently set as?
Some background information is here: http://www.kitz.co.uk/adsl/MTU2.htm
Let me know how this goes.
Thanks,
Matt
Re: Unable to access most web sites with new Linksys E4200 Router
04-05-2012 6:32 PM
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I had tried changing the MTU on the router previously, but gave it another go - no joy. (I even tried changing the cable from the modem to the router)
I followed the ping test guide on Kitz starting at 1492 and decreased it until there was no fragmentation. I had to go all the way down to a hundred before the frames stopped fragmenting.
$ ping -D -s 1472 www.bbc.co.uk
PING www.bbc.net.uk (212.58.246.92): 1472 data bytes
556 bytes from potatoe (192.168.1.1): frag needed and DF set (MTU 128)
Vr HL TOS Len ID Flg off TTL Pro cks Src Dst
4 5 00 dc05 7a33 0 0000 40 01 2eac 192.168.1.2 212.58.246.92
Request timeout for icmp_seq 0
$ ping -D -s 101 www.bbc.co.uk
PING www.bbc.net.uk (212.58.246.92): 101 data bytes
137 bytes from potatoe (192.168.1.1): frag needed and DF set (MTU 128)
Vr HL TOS Len ID Flg off TTL Pro cks Src Dst
4 5 00 8100 f9f1 0 0000 40 01 b448 192.168.1.2 212.58.246.92
Request timeout for icmp_seq 0
$ ping -D -s 100 www.bbc.co.uk
PING www.bbc.net.uk (212.58.246.92): 100 data bytes
108 bytes from 212.58.246.92: icmp_seq=0 ttl=55 time=13.238 ms
108 bytes from 212.58.246.92: icmp_seq=1 ttl=55 time=14.222 ms
I can't test an MTU of 100 on the router as that is below the minimum allowed.
I reconnected my Apple router and re-run the MTU test. In this case, the figure was 1464
$ ping -D -s 1464 www.bbc.co.uk
PING www.bbc.net.uk (212.58.246.95): 1464 data bytes
1472 bytes from 212.58.246.95: icmp_seq=0 ttl=56 time=21.449 ms
1472 bytes from 212.58.246.95: icmp_seq=1 ttl=56 time=21.783 ms
Re: Unable to access most web sites with new Linksys E4200 Router
05-05-2012 8:35 AM
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Your results confirm what I saw on your capture... that somewhere in the network, the maximum MTU is set to 128 (I saw this in the Wireshark trace you provided but I didn't really believe it and thought that my interpretation must have been incorrect).
Something very strange is going on here and I'm afraid I've got no idea what it is!
Perhaps someone in the community can come up with some suggestions. I'll chat about this with my colleagues on Tuesday when we're back at work, we're very intrigued by this problem! I never like to say this because it always feels like a bit of a cop-out, but perhaps the router is faulty?
Cheers
Matt
Re: Unable to access most web sites with new Linksys E4200 Router
05-05-2012 3:45 PM
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Re: Unable to access most web sites with new Linksys E4200 Router
05-05-2012 5:50 PM
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Quote from: Matt ! I never like to say this because it always feels like a bit of a cop-out, but perhaps the router is faulty?
Could be, but remember, this is the second router I have tried. so it would have to be faulty batch.
Hopefully your colleagues may have some ideas on Tuesday
Re: Unable to access most web sites with new Linksys E4200 Router
05-05-2012 7:09 PM
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So leahk was it a case of changing the MTU made no difference or you couldn't change the MTU for some reason?
If the latter, I'm sorry if this is granny being told how to suck eggs, but you did remember to hit a Save button and then reboot the thing?
Re: Unable to access most web sites with new Linksys E4200 Router
05-05-2012 8:36 PM
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Dan.
Re: Unable to access most web sites with new Linksys E4200 Router
08-05-2012 9:28 AM
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As Matt said, we did spot that packets were getting through and the MTU you have determined matched dead on with when they did. Whilst we did suspect MTU, we didn't really believe that the extremely low value seen could be the base value, however your test here has proved otherwise.
I'm going to try and get another scan over the capture at some point (few more priorities at hand unfortunately) and see if I spot any other patterns. It was noticed there were a number of connections that were working, which included and idle SSL connection. The capture didn't show this connection opening though, so we can't see if the session establishment had packets greater than the MTU you have determined (if they were, it is operating with a larger MTU at some point).
Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 7:43 AM
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Quote from: Anotherone So leahk was it a case of changing the MTU made no difference or you couldn't change the MTU for some reason?
If the latter, I'm sorry if this is granny being told how to suck eggs, but you did remember to hit a Save button and then reboot the thing?
The PING tests showed an MTU of 120 was required to avoid fragmentation but this is below the minimum allowed by the router.
The MTU should not need to be this low, and with a different router it works with an MTU of 1464
And yes, I did hit save and rebooted.
Quote from: Dan leahk did you look at the link I posted details on setting up the mtu on your router or are you ignoring posts from non Plusnet staff?
Dan - not sure why you are being so abrasive, especially after only 5 hours since your previous post. I do appreciate help from anyone.
Your link shows how to test and set up the MTU. These are the same tests I ran in my previous post where it was determined that an MTU of 120 was needed. This is below the minimum allowed by the router
Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 9:18 AM
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Have you initiated contact with Cisco Linksys support on this matter?
Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 9:23 AM
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Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 1:10 PM
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Questions. Do you have access to a good old Ethernet Hub (pref 10/100, and not a un-managed Switch or Switching Hub), or managed Switch with port mirroring capabilities?
Alternately, do you have access to any of the following routers: Thomson 585 (v7 or 8), Technicolor 582n?
PPPoE discovery is capable of negotiating the MTU, which is what the auto setting is for. A manual setting should over-write the negotiation. With a Hub or one of the above routers, we can capture the PPPoE discovery and authentication process and see what is generated from the the BT concentrator.
If said capture doesn't help them see the issue, I would return the unit completely as it's not fit for purpose.
Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 2:25 PM
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A shame, as I spent a lot a time narrowing down the choices to choose this router, which seemed to check all the boxes.
Re: Unable to access most web sites with new Linksys E4200 Router
14-05-2012 5:10 PM
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