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

[gazzzman]

hi there!
Sorry for the delay getting back to this
they have had me working like a slave

Originally Posted by 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

but if the gateway is inside the scope of the subnet mask it would forward it to the wan port regardless as it does not know the default gateway is wrong and therefore should be forwarded by the modem

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

if the modem is indeed just acting as a bridge and has no involvment at layer3
that would be the case

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

aha! I can now atlast (sorry for the delay here!) see where you are comming from
if the wrongly set gateway lies OUTSIDE the scope of the subnet mask on the wan interface it will be discarded by the router..
and if the gateway is INSIDE the scope of the subnet mask.. it will be forwarded to the modem regardless


"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

something wrong here? surely the packets from the router or the pc will both contain source destination and next hop information?
if so then what you are saying is when the packets from the pc get to the modem
no routing occurs untill they get to TW UBRs? and then the next hop info is stripped and the destination address is examined.. so (assuming as I am) the routers gateway address is within the scope of the subnet mask.. the same should happen?

So they will reach someone elses PC and be discarded

so that should never happen because TW UBR is only looking at the source and destination addresses the packet should be forwarded to the correct destination

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

and yes that is what I faild to realise I should have looked more closley at the earlier post that contained the network info

Thats why you werent getting any joy

I think the failure mechanism is slightly different with my modem I think it is actually doing some filtering at layer 3

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

yes I can see that if your modem is acting the way you say

finally I must say it is nice to have a technical discussion without shouting and name calling and at a level higher than "someting I saw on TV"
again thanks!

PS I am hoping I may get my modem replaced soon as I have problems with it loosing connectivity (different post lol!)
so I will be looking at this again with great interest
Garry

[Ubermik]

I might be a bit out of my depth on the intricacies of IP with the other gateway within the subnet part tbh lol, and was thinking of a non routed network behind a telewest router where the packet would be sent directly to the destination entered as a psuedo gateway and be discarded there as tho they were all on a hub with the actual telewest gateway and router also connected

So I was sort of picturing the packet reaching all clients on that network simultaneously including the gateway and then being discarded by all

Thats a likely scenario on an office lan with mixed hubs for local traffic and routers between hubs, but in hindsight I am guessing theres a routed port the other side of the modem otherwise 2000 peoples broadcasts would be eating into my downloads so it would be discarded there lol

DUH at me as that was a bit obvious really :S

[Graham M]

MAC Addresses are key

[gazzzman]

Originally Posted by Zeph

MAC Addresses are key

but only before the router
ok.. well we all got there in the end
and it was an interesting chat!!
have a great week Ubermik I feel certain we will chat some more soon
Garry

[Ubermik]

Well and you, me however am still left having to reacquire a lease on an IP then manually correct the gateway everytime my lease runs out which although that SHOULD only be once per day happened 4 times yesterday and each time it does my downloads and all internet functionality ceases

Just how flipping long does it take to manually correct the scope details for a subnet?

I reported the problem initially last tuesday, apparently the fault was caused by a server crash THREE WEEKS ago and last thursday I spoke to Telewests tier 2 support as they were still unaware of the problem and were curious as to how I was working around it, then again on saturday claiming the network team had fixed it, which they obviously hadnt lol and now today almost a week later its just happened again

As the faulty subnet I'm in is a 255.255.248 (11111000) subnet thats potentially 2,000 IP's being given out with faulty gateway information, and thats assuming its the only one thats faulty

But when I was at PC world picking up some stuff I noticed they have a notice about the fault up for their support staff, so obviously I'm far from the only person having the problem and most definitely wont be the only person they fobbed off to their £1 a minute help line who then also couldnt help

It does seem however that I am the only person who figured out it was their fault rather than the router, and was therefore the only person who had got them to refund all the calls I'd made and get a months free cable for my inconvenience

But it SHOULD have been sorted a long time ago, and most definitely since I spoke to their tier 2 support staff last week

Must be a bit of a money spinner for them eh?

[cejay]

Thanks ubermik my subnet is a 255.255.248 my router hasn't worked since last week. Connecting the modem to the pc was fine, as was the pc to the router, but connecting the router to the modem no chance. I was just about to give up on the router and its only two weeks old, when i read this so thanks alot.

[MAROSSER]

as per posts below, my subnet is also 255.255.248, and my router will no longer connect via modem, but pc will connect via modem.

really pleased i have found this thread, as i have only just ventured into the world of networking at home (literally last week), as was convinced either:

a) I was dumber than i thought!
b) my new Netgear router was fooked!

like ubermik, phoning telewaste is a test in patience and unfruitful outcomes...

in case it makes a differnece to those experiencing this problem, I live in Solihull (maybe a geographical issue with telewest?)

i'll continue to watch thread for any updates - the thought of having to continually reset the router settings to keep pace with the IP address leases is a 'bridge' too far (sorry, sorry....)

[Ubermik]

It seems to be fixed now, the second line support phoned me the day before yesterday to try reloading my settings after being told for the fourth time by their network guys that it had been resolved, this time however it appears it has and my IP and gateway loaded perfectly and I havent had a problem since

Fourth times a charm in this instance it would seem

[MAROSSER]

Hi Ubermik,

many thanks for the reply

just done an ipconfig /all and got the following:

IP Address. . . . . . . . . . . . : 82.36.191.15

Subnet Mask . . . . . . . . . . . : 255.255.248.0

Default Gateway . . . . . . . . . : 82.36.184.1

DHCP Server . . . . . . . . . . . : 62.30.192.113

DNS Servers . . . . . . . . . . . : 62.31.144.39

195.188.53.175

62.31.112.39

Lease Obtained. . . . . . . . . . : 19 January 2007 14:54:08

Lease Expires . . . . . . . . . . : 20 January 2007 14:54:08

am i right in thinking that the IP address and the default gateway here are still misaligned - do i need to do anything to update them? (ipconfig /release, ipconfig /renew).

sorry for the questions but i'm a network noob!

[Ubermik]

10111111 = 191
11111000 = 248

Carry the bits where theres a one on line two and you get

10111000 = 184


So its correct as far as I can see, the corresponding bytes are ONLY identical when the subnet has 255 (11111111) in the same byte as all bits are then carried from the IP to the gateway address "as is", anywhere there's a 0 you dont copy that bit across so on the 248 mask any 1's in the last three bytes arent copied to the subnet

But the proof is in the pudding, if its working its ok

[MAROSSER]

Hi Ubermik,

tried the router again, and now the router makes connection to Telewest, but i can't acccess the internet.

I can see that the local area connection is connected, and there is an exchange of data packets, but i can't get onto the net - any suggestions????

anyone????

cheers