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Home > Archive > alt.certification.cisco > September 2003 > Ethernet Question
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| richard carmichael 2003-09-07, 11:28 pm |
| Hi,
I'm having trouble understanding if IP addressing is used by hosts
communicating on the same ethernet LAN.
I understand that the hosts communicate using their MAC addresses. However,
won't the application on the hosts use IP at layer 3 before passing onto
ethernet at layer 2 anyway?? Does this mean that the sending hosts need to
know the IP address (using ARP if they don't know) of the rescieving host on
the same ethernet LAN before they can send data using the layer 2 ethernet
protocol?? What happens if the ethernet LAN is not connected to a router, is
IP addressing needed then??
Thanks for any help
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| edmonds_robert 2003-09-08, 11:45 am |
| If the two hosts are running ONLY TCP/IP as their network protocol, then IP addresses will be significant. As long as the computers are configured for the same IP subnet, they will be able to talk.
If you don't have a router on your network, and you want your computers to communicate, then you will either have to configure them for the same IP subnet, or use a protocol like NetBEUI; although I'm not sure why you would go this route, unless ease of setup is your major concern.
So, to answer your question, "Is IP addressing needed then?" No, it is not NEEDED, because you can run another protocol. However, if you are doing FTP between hosts, or something else that requires IP, then, yes, it is. As with any networking question, the real answer is, it depends.  I hope I have helped.
Robert | |
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| On Mon, 08 Sep 2003 03:17:39 +0000, richard carmichael wrote:
> Hi,
>
> I'm having trouble understanding if IP addressing is used by hosts
> communicating on the same ethernet LAN.
> I understand that the hosts communicate using their MAC addresses. However,
> won't the application on the hosts use IP at layer 3 before passing onto
> ethernet at layer 2 anyway?? Does this mean that the sending hosts need to
> know the IP address (using ARP if they don't know) of the rescieving host on
> the same ethernet LAN before they can send data using the layer 2 ethernet
> protocol?? What happens if the ethernet LAN is not connected to a router, is
> IP addressing needed then??
>
> Thanks for any help
No, IP addressing is NOT needed if you are using another protocol like
Appletalk, IPX, NetBIOS, etc. Or if you have some kind of proprietary
software that allows layer 2 networking. However if you are using TCP/IP,
you always need an address.
Also when going through a router, unless it also has the same protocol
compatibility, then you need an IP address.
| |
| FireSword 2003-09-08, 3:29 pm |
| Hi Richard,
Yes, hosts on the same LAN need to know about Layer3 addresses. In the
case of IP, ARP is used to create a table mapping IP addresses to MAC
Addresses.
If you do not have a router in the LAN you still need IP Addressing.
The router is only used when you want to send data to a host in
another LAN (or VLAN)
"richard carmichael" <richard@astroboy.com> wrote in message news:<nxS6b.88529$bo1.31409@news-server.bigpond.net.au>...
> Hi,
>
> I'm having trouble understanding if IP addressing is used by hosts
> communicating on the same ethernet LAN.
> I understand that the hosts communicate using their MAC addresses. However,
> won't the application on the hosts use IP at layer 3 before passing onto
> ethernet at layer 2 anyway?? Does this mean that the sending hosts need to
> know the IP address (using ARP if they don't know) of the rescieving host on
> the same ethernet LAN before they can send data using the layer 2 ethernet
> protocol?? What happens if the ethernet LAN is not connected to a router, is
> IP addressing needed then??
>
> Thanks for any help
| |
| Hansang Bae 2003-09-09, 11:25 pm |
| In article <nxS6b.88529$bo1.31409@news-server.bigpond.net.au>,
richard@astroboy.com says...
> Hi,
>
> I'm having trouble understanding if IP addressing is used by hosts
> communicating on the same ethernet LAN.
> I understand that the hosts communicate using their MAC addresses. However,
> won't the application on the hosts use IP at layer 3 before passing onto
> ethernet at layer 2 anyway?? Does this mean that the sending hosts need to
> know the IP address (using ARP if they don't know) of the rescieving host on
> the same ethernet LAN before they can send data using the layer 2 ethernet
> protocol?? What happens if the ethernet LAN is not connected to a router, is
> IP addressing needed then??
The first thing the sender does is to check the destination IP against
his own address and subnet mask. If it falls within the same subnet
(your case), then he will arp for the destination IP assuming it's not
in the arp cache already. If the destination IP falls outside of the
senders IP/subnet, then he will punt to the default gateway.
--
hsb
"Somehow I imagined this experience would be more rewarding" Calvin
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