I'm studing on this topic, and I learned that, when a node joins a network, it creates a local unicast address based on his MAC, then send a Neighbor Solicitation message to the multicast neighbor-solicited group of that address for detecting any duplicate.
Then it sends a Router Solicitation message, it receives (hopefully) a Router Advertisement message containing the network prefix, and then it create his global unicast address based on this informations.
But, as you can see in this screenshot (look at the highlighted packets), my node joins the network and sends the first NS, as described above, and then a second NS with targed address his global unicast address already built, without first sending RS and getting RA with network prefix.
Can someone explain how it gets the network prefix? Maybe it collects the RAs that the router was sending before it sends his NS? I hope that someone help my understanding this. Thanks
Could you guys help me with that question in the title? I didn't find much useful and objective on the internet to answer.
You need to understand OSI Model. Following is the answer specific to your question:
Layer 2 Communication Process:
Machine A lookup’s for Machine D MAC address in its ARP table.
If MAC Address found then packet is formed and sent to Switch A.
If MAC address not found then ARP Request is generated and MAC address is
obtained.
Switch A receives packet and checks for MAC Address in its
MAC Address Table.
If MAC Address matched it will forward packet on
matched port number.
If MAC Address not found then the packet is
broadcasted to all ports, except on which it has received the packet.
Machine D receives packet from Switch A which was sent by Machine A.
When Machine D will reply, same process will be followed as switching
is done.
Source: https://community.cisco.com/t5/networking-documents/overview-of-layer-2-switched-networks-and-communication/ta-p/3128423
I am sorry if its basics, but I did not find the appealing answer for it over the Internet.
Why only MAC is used to transfer the packet to a device ? MAC address is only obtained by ARP for a specific IP address. So, why not just let the routers maintain IP addresses of the neighbouring routers and route packets using IP addresses of routers instead of MAC addresses ?
Why not redesign the architecture, to only use IP address for routing as well as moving the packet in the data link layer too ?
Why do we need MAC addresses?" Why can't network devices such as the routers just send the packet to the next router using the router's IP address?
Note : I know that MAC address is used to identify the system in a network. But you see the source never knew the MAC address of receiver. All it knew was its IP address and MAC address of next hop.
I'm reading Data Comm and Networking by Forouzan ( Ed 5) and it says that even routers have an IP address. So why use the mac address at all. The router can store the IP address of the source and route it to the next router .
EDIT : The question that I was getting as suggestion to this one does not answer my query. There are multiple counter points and proof that I have presented here which could have been done which is not answered by the one which is suggested. So please read my question before making any assumptions.
What do you think makes more sense: Having one protocol like Ethernet handle all the layer 2 details so that its layer 3 payload doesn't have to care, or force IP, ARP, WoL, IPX, MPLS, SLPP, and dozens more implement it on their own? The whole purpose of OSI layers is that upper layers need not know all the lower layer's details and lower layers need need not support the upper layer's features.
MAC addresses are used for the layer 2 protocol which encapsulates a layer 3 protocol. If all the necessary features were embedded into IP, then you'd be leaving other protocols to re-implement layer 2 routing on their own. This would be wildly inefficient.
I am trying to create a program that will, on the raspberry pi, analyze all IP packets leaving a "Private" Network and if the packet destination is one that needs its packets encrypted, it should basically for lack of better term, intercept and encrypt that packet and then send it. All other packets for now can be dropped. SO i am just starting with it and I have gotten my pi to give me the information of incoming IP packets via TCPDump and Tshark.
I am trying to figure out how to, in C or in python, be able to compare the address of the packet to a known IP address and for now, just up a count or print that it was a match. I do not know if there is a library of functions I should install on the pi that can give me the address in a str or int, or could someone help me on the first step on how to make this function. Any documents, webpages, etc.
I would love any helping hints possible. If you need any more information please ask.
Thank You
Why do we need an IP address when the MAC address is unique? Cant we communicate only with the MAC address?
You COULD communicate using only the MAC address, but only on your local network. IP addresses are routeable, without every system on the network needing to know about every other. You just need to know a range of addresses that are on your local network, and throw everything else up to your router. The same thing happens at the ISP level. "All 216.x.x.x traffic goes that way, all 105.x.x.x goes that way..."(Obviously a gross oversimplification, but that's the basic process).
If we tried to route everything by MAC address, every machine on the network would have to maintain a list of every other participant, and it just wouldn't scale.
No. MAC addresses are specific to Ethernet, IP is independent of the underlying hardware. You can connect machines that don't use Ethernet to the Internet, if you have the required bridges.
MAC addresses are not unique. MAC addresses are reused between media. This is why wireless (802.11) and wired (802.3) may not both be present on one collision domain (see 802.1D).
MAC addresses are not clustered -- meaning that devices which are nearby in network space do not have nearby MAC addresses. IP addresses do have this property of locality. Do you intend to route packets by having a universal list of MAC addresses copied to every computer on the Internet, or do you intend to route packets to their destinations through a hierarchy of localities?
On a single collision domain, MAC addresses can be the primary addressing mode (q.v. arp and rarp). However, extension to multiple collision domains is ineffective for the above reasons.
A great professor of mine named George Varghese, now at UCSD, made the following apt analogy: You want to send someone a letter. The analogy of sending to a device anywhere in the USA based on its MAC address is like sending someone a letter knowing only their Social Security Number. It does uniquely identify someone (OK, yes, SSN isn't guaranteed unique, but suppose it was for the sake of example), but it would be very hard to find them without some giant table of where everyone lived that you could look up indexed by their SSN.
An IP address (and the similar Open Systems Interconnect, or OSI, network addresses) are more like USA phone numbers with area codes and exchange numbers: (AAA) BBB-CCCC, where AAA is an area code, BBB is an exchange number, and CCCC identifies an individual line at that exchange. There is hierarchical information encoded in that number, so that when you are far away from the destination, you only need a small table indexed by area code to determine a good "next hop" to forward the call to, rather than a table of all phone numbers in the country.
Ethernet is a Medium Access Layer protocol. It was designed specifically to connect computers on the same network. If you want to connect computers remotely located, you certainly need to jump to destination by hopping through several routers. IP (Internet Protocol) was designed with this goal in mind, hence the need for it, while Ethernet protocol does not support routing. Only some forms of primitive bridging that would not scale for something huge like the Internet.
they are used for different protocol layer.
MAC address is your device specific address. It has no relation with the geographical location, etc. you are in currently.
Ex: You can buy a cellphone/laptop in US and use it in Japan,
Australia, etc. But MAC address would remain the same. But IP address
would change with respect to the network you are connected to.
So it is difficult to route packet in an internetwork of portable devices especially.
How would it be:
Consider you have a portable network-accessing device with you on which you are using the internet. If we use only the MAC address, how would any incoming packet find the location of your portable-device. Since MAC address gives you only a fixed 48-bit device address. (The worst case scenario is using a desktop computer and having a MAC address without the IP facility. Coupling it with the static table to find your predefined location based on the MAC address, but our life is incomplete without these portable devices right?)
Thus we need some addressing scheme that can help us with addressing in a big and portable environment like internet, and thus the role of IP comes into picture, where address is hierarchal to provide a more geographically exact location.