I am using an Arduino-uno connected to a local network via an Ethernet Shield and I am trying to get the configuration information of its ethernet card (for example: IP address, subnet mask, gateway, DNS). Is there a function that allows me to get this data and save it in some variables?
You can use the Ethernet class to set and query information like IP address, subnet mask and alike.
For example, Ethernet.localIP() will return, well the local IP address.
More information here.
Related
Been Googling without success sadly.
As I understand it at the moment, data passes down the OSI Model from Transport into Network into Datalink, IP Header is added with the Source/Destination IP Address, then Ethernet header is added with Source/Destination MAC address. This is based on either local ARP lookup or ARP discovery response. However, if the IP Address is not in the local network range the frame is sent to the Default gateway, assuming one is set.
So postulating a simple example - I am 192.168.0.1/24 and I want to message 192.168.2.2/24. As my application passes data to the TCP and on to IP then to Ethernet protocols, at some point something realizes that the destination IP is outside the local network, so this needs to go via the Default Gateway, which clearly has a different IP and MAC from the final destination device. I believe the IP address of the final device is added to the IP Headers, so how does the MAC of the default gateway get added to the Ethernet Frame headers please? Is it part of the functions of the Ethernet protocol layers (if so which one) or is it at the Physical Layer e.g. the NIC?
Can I ask at what point does the Default Gateway addressing get added to the Frame? I assume not at IP as the destination address must remain in the IP header to allow Routing? So is it at the Datalink layer or even a function of the Network Adapter/NIC at the Physical layer?
I am trying to understand the functioning of the different layers in the TCP/IP stack, and I just wanted some clarification on how the link layer derives the MAC address of NICs to receive packets.
This isn't a function of TCP/IP, per se. Instead, the ARP (Address Resolution Protocol) is used in IPv4 to translate the destination IP address to the correct MAC address.
This is accomplished by the stack by first determining if the delivery is local (within the subnet) by comparing the destination to the configured network mask. If it is local, ARP will be used to generate broadcast frames at the link layer, attempting to resolve the known IP address to the known MAC address.
On the other hand, if the destination IP address is determined not to be on the local subnet, the ARP protocol will be used to send a broadcast ARP at the link layer to discover the MAC address of the router that should be used based on the configured routing table.
Using IPv6, ARP is eliminated and replaced with multicast (more specifically, solicited node multicast) using the Neighbor Discovery Protocol over ICMP6.
I have machine with two Ethernet network interfaces. eno0 and eno1. eno0 is where the internet is plugged in and eno1 has a connected Ethernet device. I got its IP through Link-Local Address method and it's 168.254.80.23. I would like to send a packet to port 5000.
I would like to use Rust's UdpSocket to connect to this address and given port and send some packet. One such packet is already correctly described in the variable buf_with_message:
let sock = UdpSocket::bind("0.0.0.0:0"); //Let system assign me an ip and port
sock.connect(("168.254.80.23",5000)); // Connect to device ip and pre-designated port 5000
sock.send(&buf_with_message).unwrap(); //Send the packet
That connection occurs as it should, but the packet is send over eno0 instead of eno1. I have no idea how to specify the interface it should use. I have found some answers that in C SO_BINDTODEVICE could be used to do this.
I have also tried assigning an IP to the interface through
sudo ifconfig eno1 192.0.2.10
and then changing the 0.0.0.0 address in UdpSocket::bind to this new address with no positive result.
I see a potential solution to go straight to raw sockets using the pnet crate but I think that would be overkill.
I am aware that RFC 3927 warns against hosts with multiple interfaces, but I didn't find any options for an alternative without ditching LLA and implementing a DHCP server.
I have started a DHCP server and I am communication over the IP that is given through DHCP. I have no idea why LLA assigned IP doesn't work when DHCP does, but it works for now.
Consider the following figure:
Now, suppose that the host with IP address 111.111.111.111 has to send a packet to 222.222.222.222. Here is what I think will happen:
The sending host will determine that the destination machine is on some other subnet, and hence there won't be an entry for it in it's ARP table. This is done by ANDing the destination IP address with the mask of the sending host's subnet, and then checking for the subnet address.
If it is determined that the destination host is determined to be off the host's subnet, then it will send the frame with the destination address MAC address of the left interface of the middle gateway. My first question: How does the host know the MAC address of this interface?
The gateway will receive the frame, and send it to it's interface on the right. In the frame, the destination and source IP addresses will remain the same, but the source MAC address will be of the left interface, and the destination MAC address will be of the right interface.
The interface to the right will receive the frame, and then will replace the source MAC address with the interface address, and the destination MAC address as the MAC address of??? The router or will be consult its ARP table to find the destination MAC address.
What is the use of the routers in between? Are frames also sent to them using their interfaces' MAC address? For example, the host with IP 111.111.111.111 would first send the frame to the router using its MAC, and then the frame is routed forward.
I am so confused right now. Can someone clear these things up?
Thanks!
Here are some comments/answers:
How does the host know the MAC address of this interface?
It uses ARP for that, but instead of MAC of the destination IP address it requests MAC of the middle gateway.
and the destination MAC address as the MAC address of???
The right host uses the same technique: it sends the ARP request to get a MAC of the middle gateway.
What is the use of the routers in between?
There is just one router and two switches in the picture. Switches are used to split collision domains, while routers are used to split broadcast domains. More on that on Wikipedia:
https://en.wikipedia.org/wiki/Broadcast_domain
I am given to understand that in order to send data using the TCP/IP protocol suite you need two IP addresses (sender and receiver). My question is, how does communication happen on an isolated LAN. Say I have two PCs connected with an ethernet cable (There is no DHCP sever and IP addresses weren't set manually), do they choose random IP addresses (to please the TCP/IP suite), or do they send IP packets with emtpy TO and FROM fields? or something else?
If you want to use IP, you must have an IP address. Most devices will auto-assign themselves an address in the 169.254.0.0/16 block if a DHCP server is unavailable.
You should also note though that there are many other protocols available, such as IPX/SPX, but most of them are not used these days.