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Unable to access most web sites with new Linksys E4200 Router

leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

I've updated the ticket witch longer captures.
Disabling the FW did not have an effect.
Thanks
mattturner
Grafter
Posts: 246
Thanks: 2
Registered: ‎25-06-2009

Re: Unable to access most web sites with new Linksys E4200 Router

Hi Kevin,
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
leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Hi,
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

mattturner
Grafter
Posts: 246
Thanks: 2
Registered: ‎25-06-2009

Re: Unable to access most web sites with new Linksys E4200 Router

Hi Kevin,
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
Dan_the_Van
Aspiring Hero
Posts: 2,484
Thanks: 1,117
Fixes: 73
Registered: ‎25-06-2007

Re: Unable to access most web sites with new Linksys E4200 Router

leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

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
Anotherone
Champion
Posts: 19,107
Thanks: 457
Fixes: 21
Registered: ‎31-08-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Hi guys, I don't know this router and this is not my area of expertise, but sometimes the blindingly obvious gets over looked as I've frequently done myself  Embarrassed
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?
Dan_the_Van
Aspiring Hero
Posts: 2,484
Thanks: 1,117
Fixes: 73
Registered: ‎25-06-2007

Re: Unable to access most web sites with new Linksys E4200 Router

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.
prichardson
Grafter
Posts: 1,503
Thanks: 1
Registered: ‎05-04-2007

Re: Unable to access most web sites with new Linksys E4200 Router

I really don't think this is physical hardware issue, it doesn't really seem like it anyway. But is most likely a firmware issue.
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).
leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Thanks for your responses - sorry for the delay in responding - I was away from home last week.
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
prichardson
Grafter
Posts: 1,503
Thanks: 1
Registered: ‎05-04-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Hi,
Have you initiated contact with Cisco Linksys support on this matter?
leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Hi, Yes I have.  They have not been able to help so far - the thread is http://homecommunity.cisco.com/t5/Wireless-Routers/Unable-to-access-most-web-sites-with-new-E4200-Ro....
prichardson
Grafter
Posts: 1,503
Thanks: 1
Registered: ‎05-04-2007

Re: Unable to access most web sites with new Linksys E4200 Router

Indeed, the help leaves a little to be desired given the details supplied.
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.
leahk
Grafter
Posts: 43
Registered: ‎30-07-2007

Re: Unable to access most web sites with new Linksys E4200 Router

I don't have access to any of the hardware you mentioned.  I've used up enough of your time on this, and appreciate the help from Plusnet and other members.  Even Cisco are now suspecting a firmware bug.  I am going to return the unit and get a refund.
A shame, as I spent a lot a time narrowing down the choices to choose this router, which seemed to check all the boxes.
jojopillo
Plusnet Alumni (retired)
Plusnet Alumni (retired)
Posts: 9,786
Registered: ‎16-06-2010

Re: Unable to access most web sites with new Linksys E4200 Router

That's a shame, but thanks for letting us know Smiley