Problems connecting via a router,,,,heres a workaround solution !

[Ubermik]

Apologies in advance for the duplicated thread, but I didnt realise it said there was a poll in the main screen, so I figured a lot might not read it because of that so here is the nekkid version


If you have a router and are having problems connecting to NTL/Telewest then heres why and how to get around it


The problem is that they have an invalid subnet which is being offered with an incorrect gateway

Routers are layer 3 devices so they wont route ANY packets to an incorrect gateway

What you have to do is manually enter your IP information but calculate the gateway address to the correct one

I was getting the following offered by DHCP

IP 082.037.160.118
SN 255.255.248.000
GW 082.047.072.001

Which wouldnt work because the gateway is on a totally different subnet, change the gateway to

082.037.160.001

and it works perfectly

Warning however, when your lease on the IP runs out if telewest still havent fixed it then if you get a different IP it will stop working and you will have to reacquire a DHCP allocated IP then do the same again. But until then the router will work

Also, if you dont know how to calculate the subnet via the IP and subnet mask its not quite as obvious as it seems as although the 160 in the third byte is copied "as is" were it to have been 163 as I had on another allocation then you would still copy 160 into that part of the gateway address. So if you dont know how to do that and just copying as is doesnt work you will need to find a util for working it out or ask someone who knows how to do binary masking as I am REALLY not going to explain it here

Hopefully this will help quite a few people to get back online through their router tho until Telewest redefine the faulty subnet scope or scopes

Mike

[MovedGoalPosts]

Duplicate thread has been deleted

So this is the only reason anyone would have a problem conecting through a router then? This post is worded like it will sort every problem out

[Ubermik]

Theres a bit of a barrage of people having connection problems ONLY via a router at the moment because of invalid subnet scopes being given out

If its a new problem despite nothing having been altered on the router and if the connection works fine if you plug directly into the modem then chances are it WILL fix the problem


But if the IP info being offered by telewest doesnt have different values in the second + third bytes of the IP to the second + third byte in the gateway then its a different fault obviously innit

Its written as a specific solution to a specific problem, because if someone DOESNT have the differing bytes then obviously it wont apply to them. If they do then it IS the workaround, so its worded as such


I hope that removes any confuddlication

---------- Post added at 23:20 ---------- Previous post was at 23:18 ----------

Actually zing, apart from the header the main thread body shows very specific criteria for what this resolves, so how on earth could anyone who ACTUALLY reads the thread body think its offered as a solution for any fault?

Originally Posted by Ubermik

Apologies in advance for the duplicated thread, but I didnt realise it said there was a poll in the main screen, so I figured a lot might not read it because of that so here is the nekkid version


If you have a router and are having problems connecting to NTL/Telewest then heres why and how to get around it


The problem is that they have an invalid subnet which is being offered with an incorrect gateway

Routers are layer 3 devices so they wont route ANY packets to an incorrect gateway

What you have to do is manually enter your IP information but calculate the gateway address to the correct one

I was getting the following offered by DHCP

IP 082.037.160.118
SN 255.255.248.000
GW 082.047.072.001

Which wouldnt work because the gateway is on a totally different subnet, change the gateway to

082.037.160.001

and it works perfectly

Warning however, when your lease on the IP runs out if telewest still havent fixed it then if you get a different IP it will stop working and you will have to reacquire a DHCP allocated IP then do the same again. But until then the router will work

Also, if you dont know how to calculate the subnet via the IP and subnet mask its not quite as obvious as it seems as although the 160 in the third byte is copied "as is" were it to have been 163 as I had on another allocation then you would still copy 160 into that part of the gateway address. So if you dont know how to do that and just copying as is doesnt work you will need to find a util for working it out or ask someone who knows how to do binary masking as I am REALLY not going to explain it here

Hopefully this will help quite a few people to get back online through their router tho until Telewest redefine the faulty subnet scope or scopes

Mike

highlighted points do not suggest that it may fix everyones problem it suggests it does. I did read your post if you had stated at the start what it was a fix for then it would have made sense

It is a good post for fixing the specific problem

[poolking]

To be a little picky here Ubermik, you don't put 0 in front of 82 or a 0 in front 47 etc.

There are people on the forums who are not into networking and just expect to plug their cable modem into their router and expect it to work, padding out the IP addresses with 0s is leading people up the garden path.

[Ubermik]

"Which wouldnt work because the gateway is on a totally different subnet, change the gateway to"

So if you DONT have a gateway on a different network obviously it ISNT the fix is it?


Admittedly the order could have been better BUT, unless someone stopped reading after a line or two it obviously isnt a networking snake oil cure for all router ills, its one for situations where the IP and gateway have different second bytes and third bytes which is affecting quite a lot of people at the mo hence why I thought it worth joining this site and posting the workaround as telewest will just direct people to a £1 a minute line the moment you mention a router who yesterday didnt have a fix or workaround either, although they might have now as I let them know how to resolve it yesterday after I sussed it


Basically tho,

1. I didnt HAVE to take the time and effort to join the site
2. I didnt HAVE to bother to let anyone else know this will resolve the connection problems if they are being given invalid IP information
3. I obviously arent getting paid for doing it so I really dont have the inclination to write a dummies guide for this so if someone thinks it is the same problem they have then thats their perogative to exploire whether it is or not

and

4. If someone cant glean enough from what I did write to know if its what their problem is or not then I really dont have several lifetimes of free time to devote to puppy walking them through it


I am guessing your some form of admin or host on here, thing is tho seeing as the purpose of the site and specifically this board is to help people "resolve" issues then nit picking contributions is just a tad counter productive really wouldnt you say?

Although it might explain why it seems such a slow moving forum compared to other sites of the same ilk I guess


Anyway, I concede it wasnt written to the same standard of clarity as a beginners guide to networking designated to be commercially sold

BUT

It DOES give a solution to a common recent problem that neither telewest, NTL, the £1 per minute tech help line OR belkin, Linksys or Netgear tech support are offering as of yesterday which is surely worth a bit less antagonism IF it helps some of your users resolve a problem they wont get a solution from anywhere else for until NTL/Telewest fix their faulty scope assignments

---------- Post added at 23:39 ---------- Previous post was at 23:37 ----------

I added the 0 so the bytes would near as damn it line up making it easier for people to see which ones didnt match but should do

Most compliant network devices I have ever used or seen DO accept the 0 instead of a space as its an accepted form of notation anyway and isnt even removed by many devices anyway despite being irrelevant

So picky? Yeah, fair description

[MovedGoalPosts]

Ok lets not start on each other please

I think the real point here is this is a technical workaround solution to a technical problem. If Telewest have messed up their networking setups to this extent then they will be receiving lots of complaints and need to get a proper reolution in place sharpish. Despite their "not supporting" routers and stuff it is a reasonable requirement of many customers to use them. Customers shouldn't need to have to mess around with such detailed setings, which realistically few would dare go near.

[Ubermik]

Thats actually why I decided to seek out sites of this ilk and post it

Apparently the problem occurred several weeks ago, but because they dont support routers when they do get a complaint they wont deal with it first line, they refer people to a 0900 number who also cant solve it and as you arent contracturally allowed to use a router, its just something they dont dissallow there isnt really an avenue to pursue and nor is it obviously an urgent thing on telewests part as it takes about 10 minutes to reallign a subnet scope, not three weeks lol


It does appear however that nobody has actually gone back to them yet pointing out that it IS their problem even tho its being "highlighted" by routers hence them still fobbing people off and hiding behind the "we dont support routers" mantra which IS probably why it has been going on for so long and people have it appears been having to just connect one PC to the modem and not use their routers



So more simplistically, IF you cant connect via a router but have no problem connecting when you plug into the modem AND it was fine and nothing has been altered then it is likely to be this problem

So even when someone cant even understand what I have written, even when they dont know how to put it into practice they will be able to not be fobbed off by telewest tech support and will be able to get them to deal with the problem

Which might then in turn mean telewest will actually spend the 10 minutes fixing the faulty scope or scopes and might even tell the first line support staff to stop sending people to the pay per speak line which they also run and financially benefit from


As an add on, anyone who does have this problem should then be able to get re credited on their phone bill for any calls made in pursuit of it, I have had both my calls to the telewest 0900 line as well as several calls to two router manufacturers support lines wiped off the bill as well as getting a months cable for free for the inconvenience and am also now going to be chasing them to try and get some recompense for the additional router I purchased before I realised what the actual problem is

All of which are avenues anyone else who has had this problem can pursue

[gazzzman]

hi there!
just a quicky!
as the pc connected directly to the modem (via ethernet) obtains its
DHCP information in the same manner as the router would, and the PC works ok when directly connected to the modem..
I am somewhat at a loss to explain how one is allocated the correct gateway address and the other isnt.
I wonder if we may be seeing a problem relating to router firmware as opposed to
a misconfiguration of the DHCP server?
interesting that one
cheers
Garry

[Ubermik]

Garry, the reason for that is twofold

The first part of the reason, why the router doesnt seem to even try and send packets is because its a layer 3 router

Either it will just decide to not bother routing any LAN traffic to the modem because the gateway is wrong or the actual act of routing the packets itself will fail due to not having a valid destination on each attempt although the effects will be identical in that no traffic will get from the lan to the WAN side of the router, the only real difference being that one will be due to each individual packet being discarded and the other will be due to it simply ceasing to route due to the lack of a valid gateway which will depend on how the firmware is written for the router


The reason it WILL work when connected directly to the modem is because the modem isnt a router so it wont wrap any routing information around the packets, that will instead be done by Telewests routers who dont rely on the packets routing information for the gateway but which use their own routing tables which will contain the real gateway for each subnet meaning it will carry on its way merrily

---------- Post added at 01:37 ---------- Previous post was at 01:34 ----------

So basically the information the router and PC get are identical, but the router being a router is what means it doesnt work

If you connect the PC directly to the modem and then do an ipconfig or ipconfig /all you will see the information thats tendered by the DHCP server is still just as wrong and will be identical to that the router obtains when its connected between the PC and the modem

I hope that clears it up

Mike

[gazzzman]

Originally Posted by Ubermik

Garry, the reason for that is twofold

The first part of the reason, why the router doesnt seem to even try and send packets is because its a layer 3 router

now please feel free to correct me but..
dhcp is a layer 2 protocol

Originally Posted by Ubermik

Either it will just decide to not bother routing any LAN traffic to the modem because the gateway is wrong or the actual act of routing the packets itself will fail due to not having a valid destination on each attempt although the effects will be identical in that no traffic will get from the lan to the WAN side of the router,

well we agree so far as the packets will exit the wan port of the router their destination ip address will be wrong and thus will be discarded at the isp's router
but afaik the modem isn't exactly that.
it infact is a dsu/csu & performs protocol conversion as well as the act of modulation/demodulation..
now what you are saying here is perfectly correct when using USB
but when using ethernet the packets should be sent to a valid gateway address
if you are right in your explanation that means that all the modem actually is infact is a bridge!
even then I am surprised and the ntl modem must work differently
I have just tested this by connecting a windows host directly via ethernet to my cable modem and unless I specified the correct gateway address in the os
I had no connectivity!
as soon as I correctly specified the gateway address connectivity was restored!
I am using an anbit modem here btw

Originally Posted by Ubermik

the only real difference being that one will be due to each individual packet being discarded and the other will be due to it simply ceasing to route due to the lack of a valid gateway which will depend on how the firmware is written for the router


The reason it WILL work when connected directly to the modem is because the modem isnt a router so it wont wrap any routing information around the packets, that will instead be done by Telewests routers who dont rely on the packets routing information for the gateway but which use their own routing tables which will contain the real gateway for each subnet meaning it will carry on its way merrily


---------- Post added at 01:37 ---------- Previous post was at 01:34 ----------

So basically the information the router and PC get are identical, but the router being a router is what means it doesnt work

If you connect the PC directly to the modem and then do an ipconfig or ipconfig /all you will see the information thats tendered by the DHCP server is still just as wrong and will be identical to that the router obtains when its connected between the PC and the modem

I hope that clears it up

Mike

fascinating.. I would really be interested if you could try this in the way I did and post the results
I mean REALLY interested!!
what midem are you using?
sorry if I sound a little shouty (if there is such a word) but it's my work we are talking about here and if I am wrong I need to know
thanks a lot for your explanation; I look forwards to hearing your results and what type of modem you are using!
thanks again
Garry

[Ubermik]

Firstly I dont quite get the relevance of what layer DHCP might be, its a one time deal which would have been completed before a packet is even attempted to be sent to the internet

That aside the router will wrap or try to wrap wan aimed packets with the gateway address and will then not send it because it fails the validity check or having established the gateway was flawed at setup will just not be routing at all

The modem on the other hand IS just that, it doesnt attempt to route or wrap the packets and does just act as a bridge leaving the routing to the router as far as I'm aware

As for what happens when I "do it", thats already outlined in the original post

With the bogus gateway supplied by telewest I get absolutely no traffic to the modem from the router at all (I have a netgear router which shows packets to and from the modem on a statistics page), so theres no net access at all

When I connect one of the PC's directly to the modem it picks up exactly the same IP information but works flawlessly and I have full internet access

If I manually enter the IP information with the correct gateway into either the PC or the router both still work perfectly



When you say a "wrong" gateway in your experiment what does that mean?

Some random but wrong one or an actual wrong one supplied by telewest but still part of their IP address pool? Because the first one I wouldnt expect to work with either the PC or the router connected to the modem, the second wont work with the router but will with the PC


I have the SB3100 modem, so its only an ethernet connection with no USB facility BTW

[gazzzman]

Originally Posted by Ubermik

Firstly I dont quite get the relevance of what layer DHCP might be, its a one time deal which would have been completed before a packet is even attempted to be sent to the internet

That aside the router will wrap or try to wrap wan aimed packets with the gateway address and will then not send it because it fails the validity check or having established the gateway was flawed at setup will just not be routing at all

The modem on the other hand IS just that, it doesnt attempt to route or wrap the packets and does just act as a bridge leaving the routing to the router as far as I'm aware

yes but the packet is already encapsulated with the next hop (ie gateway address) at the pc wether or not it is connected to a router if this is not valid there is no reason for the modem to look at it as "interesting traffic" and would ignore it?

Originally Posted by Ubermik

As for what happens when I "do it", thats already outlined in the original post

With the bogus gateway supplied by telewest I get absolutely no traffic to the modem from the router at all (I have a netgear router which shows packets to and from the modem on a statistics page), so theres no net access at all

now hang on a min.. the pc should recieve your router address as the gateway
address and by your reasoning if the modem just accepts packets from the pc encapsulated with the wrong gateway address and forwards them regardless
to the isp's ubr then after leaving the wan port of the router the packets from the router should "look" the same as the packets would look from the pc if it where using the modem directly! all the router does with the transmitted packets after NAT is encapsulate the packets in the same way as the pc would (source & destination)
so.. the fact the router has the wrong gateway address "should" have the same result as the pc with the wrong gateway address!

I am not having a go or anything I spent 2 years getting my CCNA and another getting network+ if there is something I should understand but dont here I need to get my head round it

Originally Posted by Ubermik

When I connect one of the PC's directly to the modem it picks up exactly the same IP information but works flawlessly and I have full internet access

If I manually enter the IP information with the correct gateway into either the PC or the router both still work perfectly

When you say a "wrong" gateway in your experiment what does that mean?

Some random but wrong one or an actual wrong one supplied by telewest but still part of their IP address pool? Because the first one I wouldnt expect to work with either the PC or the router connected to the modem, the second wont work with the router but will with the PC

I tried an assortment of gateway addresses in the same subnet as the correct gateway address and got the same result with 2 routers and 1 pc the routers I used btw where and old cisco 4000 series and a draytek 3300v
I really need to get my head round whats happening here!

Originally Posted by Ubermik

I have the SB3100 modem, so its only an ethernet connection with no USB facility BTW

I dont actually know that modem but I will research it tomorrow
thanks and have a great weekend
Garry

[Ubermik]

Thats the point tho, they never DO leave the router in the first place because it IS a router so it doesnt even bother sending them to the modem because the gateway is incorrect

The PC nor the modem looks at the routing information so even with an incorrect gateway packets flow as freely as guiness on st patricks day


So yes IF the router would send the packets to the modem they WOULD be forwarded as they are from the PC, they would have an extra layer of information wrapped onto them by the router compared to the same packet from the PC, but to the modem thats irrelevant as it just sends whatever its sent to the telewest router and lets that sort it out, but the "IF" is the critical word there as they arent sent to the modem, they never get to the wan side of the router to begin with so the modem cant forward packets it hasnt been sent to begin with no matter how good a modem it might be


"I tried an assortment of gateway addresses in the same subnet as the correct gateway address and got the same result with 2 routers and 1 pc the routers I used btw where and old cisco 4000 series and a draytek 3300"

But all other locations bar the actual gateway in that subnet will be a PC and WILL be obtainable without any routing being needed BECAUSE they are on the same subnet

So they will reach someone elses PC and be discarded

The difference with the ACTUAL fault is that the gateway address ISNT on the same network, so it DOES neet to be routed and despite having the wrong IP for the gateway is automatically sent to the actual gateway for that subnet merely because its not for a local destination on that subnet

Thats why you werent getting any joy

Try entering any other gateway from any other Telewest subnet you can find and see what happens then, because its not on the same subnet as your PC it should then be sent automatically to the correct gateway by telewests router

Infact in theory the same might happen with any real world IP that isnt on the same subnet as the host, similar to a two status rule

1. If the final destination is on the same subnet send it to the destination
2. if its not on the same subnet send it to the gateway

For rule two tho the packets gateway information is irrelevant as the telewest router already knows its own gateway to begin with so it just peels off the incorect jacket applied on the PC and possibly reapplied by the modem and then replaces it with an acurate one

The same would happen if the residential gateway/router just forwarded the packets knowing they were wrong but that is where the problem lies, they dont even try

Hence there being no internet connection with the router inline but perfect internet connectivity when connected directly to the modem

Which then leads the telewest support staff to claim its a router problem and therefore isnt supported which is how it sort of looks but isnt as the router is working within the rules of subnetting and is acting as it should do