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New Member

lan problems

Hi guys

I need help on this two cases

case one

I have a cisco 1750 router connect strait to the pc using a crossover from the router to the conveter and a straight cable from the conveter to the pcbut this lan is not coming up.when i do sh f0 it shows up/down i changed the cables and conveters and the network card on a pc but still is down

but when I set keepalives to 0 it comes up/up and pingable but still i cant see the pc.my question is because I changed the cables and card on a pc, is this a problem with my router'sether port. and why when i set keepalive to 0 the interface becomes pingable is this testing that the ethernet is faulty or not? please help me with this because the only thing left is to swap out the router.

case two

this cases are little bit similar.I also have same router 1750 and connect strait to the pc using cross over from the router to the converter and straight cable form converter to the pc but in this case the ether is up/up but i cant see the pc but I can see its address on arp table but cannot ping it even here we swapped out thecables and card on a pc but still cannot see the pc

and the collission light is on(orange colour) in front of the router

I cannot figure out where the problem could be please help

thanks (in advance)

  • Other Network Infrastructure Subjects
3 REPLIES

Re: lan problems

In both cases: for straight-through connection, you will need a crossover cable crossing pairs 1-2 with 3-6. Through keep-alives, the router receives its own loopback testpackets. This only works on a hub.

New Member

Re: lan problems

On case two, check your duplex settings on both your pc and your router. It looks as though you may have a duplex mismatch. Check in case 1 also. I can't quite determine the problem in case 1, but if you can check the duplex settings, we can move on to the next step...

-Bo

New Member

Re: lan problems

It sounds like you have physical layer problems in both cases. The keepalives are a way for the router to see traffic on an interface to verify that it is working. If the router sees these packets coming back to it, it assumes that the link is good and sets the line protocol to 'up'. When you turn off keepalives the router does not send these packets and does not rely on them. It simply turns the interface up. This is useful for testing when the interface is not connected or there is a problem. You can turn off keepalives and ping the interface. If this is good, the router is probably good - look elsewhere for the trouble. I have used this when I have installed a router but the LAN was not yet ready for service. You have done this test and the router passed. By the way, this test is valid when connect to any other network device (hub, switch, router, PC, etc.) or when the router interface is not connected at all.

I don't know what you are using for a converter or your exact physical topology, but the rules don't change. Transmit goes to recieve and recieve goes to transmit. I have used electrical to optical converters for both Ethernet and token ring. These devices simply extended the wire (did no crossover) so I had to do the crossover as though the devices were next to eachother. Look at the devices that you are using and think about what they are doing.

Further testing: Bring the PC to the router or the router to the PC and connect them with a known good crossover cable. Do they come up? Check both ends. Remember, this is a full duplex circuit. You can have one pair good and one pair bad. If the PC and the router work when they are next to eachother, move them back to their permanent location. Do not change any settings!!! Now work on the proper connections for your converters.

Another test: At the PC, open a DOS prompt and type 'ping localhost'. This is a test of the TCP/IP stack in the PC. If that works, type 'ping x.x.x.x' (your IP address). This will verify that the IP address that you think is on the PC is actually there. Good luck and good hunting.

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