about crossover/rollover cable and the extra question

hey guyz i returned after a while

and have some questions for learning the true things

first one , while connecting from PC to router or reverse of it
we can use either crossover cable or rollover cable
but what is the difference about them WHILE CONNECTING TO THE ROUTER FROM PC OR REVERSE?

second question will be so easy to you but i ask it whatever you say
i want to connect to the internet at home and i have adsl modem and a NIC
card in my PC . But there is the thing i am confused is this :

adsl modem seems to connect me to the internet but there is a NIC
also so which one provides me the internet?(and i found somewhere modem is at the first layer of OSI so but this machine has ethernet , dsl ,USB and internet buttons on it how can it provide me these if it is
at first layer?

please reply i am confused

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Comments

agustinchernitsky

A rollover is when you connect the PC to the Console Port of the Router.

The crossover is used when you connect the PC to the E0/0 or Fa0/0 of the Router.

loboernesto

first one , while connecting from PC to router or reverse of it
we can use either crossover cable or rollover cable
but what is the difference about them WHILE CONNECTING TO THE ROUTER FROM PC OR REVERSE?

^^ There's a big difference between the two but basically when using a rollover cable attached to the console port of the router you are accessing it through the line console 0, you are not connected to any network (there is no routed protocol configuration in a console port nor in the serial port of the PC).

when connecting to a router using a crossover cable you are making a network connection, traffic flows from one another, etc. you are not accessing the router unless you use telnet (for remote configuration)

Something you want to remember is that a accessing the router via the console port lets you troubleshoot the router by debugging, and you can also make password recovery and screw the network configurations up and still have access to the router, and probably many other things.

adsl modem seems to connect me to the internet but there is a NIC
also so which one provides me the internet?(and i found somewhere modem is at the first layer of OSI so but this machine has ethernet , dsl ,USB and internet buttons on it how can it provide me these if it is
at first layer?

^^ You access the internet through the telephone line, what the modem does is translate the analog signal into a digital signal so your NIC or USB port can understand it. A modem is a Layer 1 device, it works with voltages and bits. All it needs to do is modulate and demodulate the signals, it doesn't care about layer 2 info (physical address) or layer 3 (logical), but the raw bits it transmits are used by the other layers each doing its function.

hope it helps a bit. I know my explanations are a bit confusing...neither English or networking are my native languages!.
cheers

kobem

loboernesto wrote:

^^ There's a big difference between the two but basically when using a rollover cable attached to the console port of the router you are accessing it through the line console 0, you are not connected to any network (there is no routed protocol configuration in a console port nor in the serial port of the PC).

so why do we use rollover cable if we don't connect any network?

^^ You access the internet through the telephone line, what the modem does is translate the analog signal into a digital signal so your NIC or USB port can understand it. A modem is a Layer 1 device, it works with voltages and bits. All it needs to do is modulate and demodulate the signals, it doesn't care about layer 2 info (physical address) or layer 3 (logical), but the raw bits it transmits are used by the other layers each doing its function.

and if the modem is at first layer what are the buttons on it for use?

loboernesto

so why do we use rollover cable if we don't connect any network?

The rollover cable isn't a cable suitable to access a network. It's similar to a UTP cable, it's made of the same materials as well but It wouldn't be able to transmit data if it was much longer since it's not twisted and therefore is very susceptible to RFI. all it does is connect the PC's COM port (serial port) to the router's console port. the pins are different as well....they are rolled over as the name implies. I hope that makes it clearer.

and if the modem is at first layer what are the buttons on it for use?

I'm not sure I get your question there, I haven't seen your modem neither but here I go:

When you read that a device is a layer 1, 2 or 3 what it means is that the primary function that device plays is a layer 1, 2 or 3 function. Your modem may have different buttons on it (my one doesn't have any), but its function is still a layer 1.

cheers.

Danman32

Rollover: Essentially you are connecting to the router via a serial connection, as if you were connecting to and managing an external dialup modem. Lots of network devices have a serial connection to directly manage the device, since you don't get a screen and keyboard with them. The PC becomes the screen and keyboard for managing the device, in this case the router. On the PC, you use a terminal emulation program to comunicate over the serial line.
Do not confuse this with Telnet, where you essentially do the same thing, but over IP. If you don't already have a network (IP) connection between the PC and the appliance, you'll have to connect to the console port which is strictly RS-232 serial.

As for your modem, it is a level 1 device, though there may be internal aspects of it that has level 2 characteristics. The connection between your PC and the modem is ethernet, but the protocol is PPPoE or PPP over Ethernet. Basically you are tunneling PPP over ethernet to the modem, which then forwards the PPP to the ISP. Many modems nowadays can also connect via USB, which might make the matter appear clearer to you.
Either case, the public IP is assigned to your PC, not to the modem.

pannupandit

I am also using ADSL modem for internet and using USB port to connet it to my PC but there are two network connections...appeared on the task bar.! is of private range i.e. 192.168.0.0 range and one connection is of public range..which i am using to access the internet. i AM LITTLE BIT CONFUSED....how it is happening ..can anybody telll me?

loboernesto

I've got a wireless router so my case is different... but I would say that the private address is your network card (PCI) and the public address is your the logical NIC that your USB creates which connects you to the internet.
This is what I would say it is but I don't really know how USB ports function when you use them with an ADSL modem....I'll look into it.. is interesting and will be probably useful to know more in depth.
In my case my network card (wireless one) has a private address 192.168.1.2 but the wireless router NATs it to the public address provided by the ISP.
Cheers

cambei

pannupandit wrote:

I am also using ADSL modem for internet and using USB port to connet it to my PC but there are two network connections...appeared on the task bar.! is of private range i.e. 192.168.0.0 range and one connection is of public range..which i am using to access the internet. i AM LITTLE BIT CONFUSED....how it is happening ..can anybody telll me?

Somebody please correct me if I am wrong. But this sounds to me like it is actually an ADSL router/modem that you are connecting to via USB. So the modem (layer 1) is part of the router and passes the data to the router (layer 3) part of it. Probably it is a switch (layer 2) also and allows you to collect multiple devices. The router would be assigned the public IP and the devices which connect to it would be assigned IPs in a private range.

I am not saying this IS the case, I just cannot see why a simple ADSL modem would need a public and a private IP.

loboernesto

hi cambei,
if pannupandit is able to see a network card in his computer with a public address I don't think he is using an ADSL router/modem. if he did use and router/modem the one with the public ip address would be the router (not the pc) and all the other devices connected to the lan interface would receive a private address from the DHCP working in the router. They will connect to the internet through the router which will NAT the private addresses to its public address using PAT.
If the ADSL device is only a modem it will not posses any IP address...the NIC of the pc will be set to get the IP address dynamically and the ISP will assign one to it. An ADSL router/modem will probably have 2 ip addresses, but only one will be a public address and that will be the interface that "faces" the internet, the other ip address will be the public one connected to the PCs (the LAN)
So, if he is seeing two network cards (I presume one is the PCI NIC and the other is the USB port acting as a network card) and one of them has a public address i would say he has a ADSL modem, not a router/modem
But same as you, that is what I think it is...

cheers

cambei

Yeah I understand NAT/PAT etc. In your example, the pci NIC has nothing to do with the internet conection. I assumed that the poster would know whether or not it was involved or not.

My thought was that in Windows, when you connect to a router, it does show up in your network connections as the Internet Gateway. You can also usually see the public IP via this.

Guess we just need more clarification from the poster. I know that this post will probably not amke much sense as it was not worded very well, but I am at work :P

loboernesto

Yeah, you are right.
I've seen what you says about the Internet Connection appearing on windows, I think it comes up when you get access to the internet using ICS though(the address of the gateway wouldn't necessarily be a public address in that case i think), but not sure... i think i had ICS enabled on my pc to share with the vmware machine but that was a while ago and I can't remember very well.
well I let you go on with your work, I finished work about 4 hours ago. Being a baker is killing me!! got to get up way too early.

cambei

Lol. I've not even had lunch yet!!

The gateway device does not have to be a Windows machine runnign ICS, as my Speedtouch router shows up like this in my home network.

loboernesto

No it doesn't...same as you my gateway is a router. You may have a different set up though, my pc doesn't have any configuration related to public addresses and as default getaway i have the router's "inside" interface ip address not the public address...but as I said you may have a different set up and my experience with this goes as far as my home network does

.
cheers

Danman32

How about posting output to 'ipconfig /all'?
Be sure to alter the public IP to something like 99.99.99.99 for security, but still identifying it as the public address.