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I understand that a router uses NAT to translate the public IP we get from the ISP to say 300 local IPs. Does a switch perform the same function? If not, how's it different?
No, a switch cannot perform NAT and translate public(s) IP addresses into private addresses.
A switch is a network device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2). So, they are not aware of IP addresses which are network layer (layer 3). A switch keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times.
Routers are network devices used to interconnect two different networks (with different IP addressing schemes).
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ARP and RARP are the main Protocol uses in Link Layer. To do the ARP request, a device requires IP and MAC address pair for broadcasting. So my question is ARP doing the mapping the IP to MAC by referring the data
and operates using the LAN.
So RARP is the reverse algorithm of that like mapping logical address to physical address in caches in Computer Systems.
I hope a good answer from the community.
There are dozens of protocols that use the data-link layer the same way ARP does, including IPv4, IPv6, etc. See IEEE 802 Numbers for a list of protocols that use the data-link layer.
For protocols in the data-link layer, there are/were many. For example, token ring, ARCNET, FDDI, frame relay, HDLC, ATM, PPP, etc. Ethernet used to be the king, but Wi-Fi has dethroned it since there are more devices shipping with Wi-Fi interfaces than devices with ethernet interfaces.
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I have a HP ProCurve switch, I recently added 2 new machines to the network, which I had to assign the IP addresses to manually. Now using these 2 machines I can ping my current machine and other machines on the network, however if I try to ping those 2 machines from my current machine (or others on the network) it does not go through. So my thoughts are that the router table has not updated so that's why I can't ping them from machines that have been on this router.
(Not too sure, not enough knowledge yet)
At least I think so. My question is does the Router Table update it's information automatically?
Assuming your HP Procurve is acting only as a switch, then the Routing Table should not be your problem. A switch does not route IPs, a switch is concerned with routing packets via their layer-2 addresses (MAC addresses). The switch determined which physical port is connected to a device with a MAC address, and when it gets a packet addressed to that MAC address, it sends the packet out that port. The mapping on port to destination mac address is stored in a CAM table inside the switch. This is very different from a routing table that maps IP address ranges to physical interfaces.
What is probably happening is that ARP is not resolving. ARP binds layer 3 IPs to layer 2 MACs in a local network. This can be cause for a few reasons. The first thing i would look into is if the switch has VLANs enabled. This makes the switch act like multiple isolated switches. After that you may need to look at your computers ARP tables to make sure they are correct. The arping command will be useful.
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So, i was reading networking in depth. One concept i failed to understand was how different machines in LAN manage to access internet through one public IP address provided to company by ISP.
For eg. let's say the public address provided is 244.13.5.89. And all the machines when get to internet, they all are recognized as 244.13.5.89 despite their private address being 192.168.3.x, which is fine. But now when the router sends the request for each of these machines, how does it maps each response to respective machine?
If the answer is NAT, what entries does NAT has? Is there port no. or something else?
I will give you the idea about the complex case scenario :-
If all datagrams arriving at the NAT router from the WAN have the same
desti- nation IP address (specifically, that of the WAN-side interface
of the NAT router), then how does the router know the internal host to
which it should forward a given datagram?
The trick is to use a NAT translation table at the NAT router, and to
include port numbers as well as IP addresses in the table entries.
See more details about NAT Table here.
SORRY, don't know why it took me minutes to post an answer, it was not allowing me to add the answer...
NAT has following fields:
source computer address and website, so when it receives packet it will replace source computer address with its public address, and send it to the internet once response comes back it sees oh this come from the website and it was requested by the source computer. It will again replace destination address with source computer address and send it in LAN.
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I'm trying to understand NAT (Network Address Translation) .
Can someone explain how can I determine if my computer is using a NAT (behind a NAT) , or
if it using its own IP address ?
What Barmar said in the comments is the easiest way. Obtaining your IP address over HTTP is indicative that you are behind either a NAT or an HTTP Proxy server. (I suppose it's possible you could have a public IP address, but your device is configured to route HTTP over a caching proxy).
Formal NAT detection and NAT classification can be done with the STUN protocol or equivalent protocol in which a UDP or TCP service echoes back the IP address back to the client that connected to it.
Another telling sign if you are behind a NAT is that your local IP address is in a private IP address range such as the 192.168.x.y range, the 10.x.y.z range, or then 172.16.0.0-172.31.255.255 range.
And pretty much any Wi-Fi setup is going to be a NAT configuration.
The NAT detection technique is based on two observations about the IP TTL (Time To Live) field.
Host operating systems have characteristic initial TTL values. This property of individual operating system implementations of TCP/IP is well known and can be used as part of a "fingerprint" to identify the operating system that a host is running merely by examining its traffic.
NAT devices or gateways decrement the TTL on packets that they forward.
For more details visit: http://www.sflow.org/detectNAT/
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whats the purpose of local IP addresses if there are mac addresses? ARP maps mac addresses to IP addresses but I don't see why it's needed, because I thought data on LANs are sent as frames which only care about the mac addresses.
Long ago and far away, there was more to the world than Ethernet LANs, and application writers didn't care whether your PC was attached to an Ethernet, a Token Ring, an XNS net, or dial-up. IP provides a layer of abstraction and coherence across the top of all those and many more, allowing application authors to ignore the differences between them.
And what happens if you want to talk to a macine that isn't on your local area network (such as StackOverflow).
IP allows routing of packets anywhere, not just locally in your current network segment and, though it's mostly over Ethernet now, IP can equally well work over other underlying layers, giving a consistent view to the upper layers. This is vital given how much stuff is actually built on IP (DNS, FTP, SSH, HTTP and so on).
Machines almost certainly will cache IP-to-ethernet details to speed up subsequent transfers so the impact of translation on the LAN isn't so bad.