I would like to send data between two ethernet interfaces that are connected with a crossover cable in Linux. The two ethernet interfaces are on the same box. I defined the ethernet interfaces to have different static ip addresses (1.2.3.4 and 5.6.7.8) and have been using sockets to send bytes from one IP address to the other. I want to emphasize that I want the data to leave the box one interface of the box and get received on the other interface of the same box. One consequence of this is that unplugging the cable would prevent communication between the client and server on the same box.
The kernel is smarter than me I guess and decides it doesn't need to send information out on the wire and routes the data directly between the sockets internally, thus negating the test. I have tried to use SO_BINDTODEVICE to force the client to send data out of a particular interface, but the server never sees it. I am really stuck and this doesn't seem like it should be this difficult.
There are two entries in the route -n table
Dest Gateway Genmask flags metric use interface
1.2.3.0 0.0.0.0 255.255.255.0 U 0 0 eth0
5.6.7.0 0.0.0.0 255.255.255.0 U 0 0 eth1
You can not communicate using IP between 1.2.3.4/24 to 5.6.7.8/24 without going though a router. The problem is that IP can only talk to other computers in the same network segment. To calulate the network address you need to do a logic AND between both the interface address and the subnet mask. This will give you the network addresses. If the two network addresses are different then a router will be required. In your example you will have network address 1.2.3.0 and 5.6.7.0. Because these are different it will will to send data.
More importantly most network stacks are smart enough to see that if both interfaces are on the same computer it will not send the data all the way to the phyical interface. It will probably only send the message though the IP stack. But again it would need to be vaild address for it to work.
You should even be able to test a similar setup using just loopback network devices. (virtual network cards.)
Try using the following two IP addresses:
192.168.64.1
192.168.64.2
I'm not sure this is the problem, but 1.2.3.4 and 5.6.7.8 aren't on the same subnet. (Because when you apply the mask to each one, you don't get the same network address, as the Dest column is showing you.)
Related
Hello Stackoverflow experts,
I have been struggling with how to use the ip fragmentation provided by DPDK. and was wondering I have the correct concept of IP address and the MAC address used in rte-mbuf ethernet header.
Is Ip address alone in the header of rte-mbuf can be used to transfer from local to remote?
I see in the DPDK sample applications that the ip address is used in the hashed tables such as IP fragment table after the packets are received, but the fact that data is actually received just by using ethernet mac address, gives me the impression that IP address is only defined by the DPDK user (developers using DPDK API) and not used in actual data transfer.
Is there something missing to what I understand?
You are right. Most DPDK examples work on the second level of the OSI model, i.e. they only care about MAC addresses, not IP.
The IP reassembly example is based on L2 forwarding example, i.e. it acts as an Ethernet bridge. Though, it requires IP addresses to be analyzed, i.e. source and destination IPs must match for all the fragments of the same flow.
Now answering your questions:
Is Ip address alone in the header of rte-mbuf can be used to transfer from local to remote?
If you mean transfer using rte_eth_tx_burst() then no, IP header is not enough. The ethernet header must be filled properly as well.
IP address is only defined by the DPDK user (developers using DPDK API) and not used in actual data transfer.
Since the reassembly example is based on L2 forwarding example, it acts as reassembling Ethernet bridge. So you have a right impression, this example does not route packets based on IP addresses. It just uses IP addresses to reassemble IP fragments.
I am writing a discovery program, written in C++ that will run on linux, to enable me to determine if certain devices are connected to the network. I have the Mac Address of the other devices and I need to resolve their Ip Addresses.
I have checked /proc/net/arp and the devices don't appear.
I tried pinging the broadcast address and this doesn't reach the target and therefore the ARP cache is not updated. However, if I ping the ip address directly it is (but this is not an option).
Also, the devices can be configured with either static ips or can get them via dhcp.
Is there any way that I can determine the ip addresses given the Mac addresses?
Some years ago I'd have suggested to use RARP but it is not supported by Linux kernel any more. Unless there is already a solution I would suggest you the following home-made solution:
-You can use Packet sockets to implement your own Layer 2 protocol: instead of using IP as payload of the Ethernet frame you can select your own protocol code (for example: instead of 0x0800 for IP use 0xABAB, always a number greater than 1536)
-In each node you implement a simple server that use packet socket to read the frames with that protocol code or you could use pcap, as you prefer.
-Whenever you need the IP address of another node you send an Ethernet frame to that MAC address. The server will read the new frame and respond with another frame conveying its own IP address.
-If you choose this solution please remember the payload has to be at least 46 Bytes long, so you may need to use padding. Also you can use the TLV (type length value) format for your own protocol.
Read this:
http://en.wikipedia.org/wiki/Ethernet_frame
http://man7.org/linux/man-pages/man7/packet.7.html
I hope this helps.
I'm trying to write a function that can get me the IP adress (and the name of the device as bonus) of devices that are in my network, the network is gonna be a direct connection between two computers using Ethernet cable or creating an access point (using wi-fi)
I tried to search about how to do it but it seems like I need to listen to the network or something which seems to be difficult.
hope you can guide me to what I should do or read to get started.
Note: I'm using Windows on both computers.
Edited:
P.S: I need the IP Address so I can send a message to the other computer using winsock in a Client/Server program I wrote.
can't I make the server send its IP to the client or the opposite ?
If your software is running on both machines, you can have one (or both) machines send out a particular broadcast (or, if you prefer, multicast) UDP packet on a specific port. Your program should also be listening on that same port. When it receives that packet (using recvfrom()), recvfrom()'s fifth argument will contain the IP address of the machine that sent the packet, i.e. the IP address you want.
(If OTOH your software is not running on the remote machine, you'll need to use some more general-purpose discovery mechanism such as mDNS or LLDP -- hopefully you won't have to do that, though, as it's a good deal more complicated)
I am using the Microsoft code here to learn how to detect IP addresses of cards and devices:
http://msdn.microsoft.com/en-us/library/aa365949%28v=VS.85%29.aspx
I notice some strange behavior.
I have a system with two ethernet cards; one is connected to the internet and one is connected to an ethernet device. When I run the sample code, it will always give an IP address for the card that has the internet connection, but the other card will come up as 127.0.0.1 with a subnet mask of 255.0.0.0 unless I have the ethernet device plugged in and powered. But the card should have a default IP address whether its actually connected to anything, right? How can I modify this code to detect that?
There's a third IP address detected that appears to be just empty data. I tried this on another computer with a single network connection and it also detected a second, non-existent connection. Each time, this connection has an IP address of 127.0.0.1 and a subnet mask of 255.0.0.0. What does this represent?
Given the demo code, would this be easy to edit to be able to detect IP addresses of devices on the network that any card is connected to? I really just want to detect the IP address that a single ethernet device is set to. The device is directly connected to the card. The reason I want to do this is because the device and card obviously don't play nice when their subnets are different and I want to detect when this is the case.
Thanks!
R
That address of 127.0.0.1 is not the address of the other card. It is the address of the loopback adapter - a virtual IP address that can only send and receive data with itself. The other NIC (that isn't plugged into a network) is simply not in the address table.
You may just want to call GetAdapterAddresses and filter out all adapters with an IFType of IF_TYPE_SOFTWARE_LOOPBACK.
If you want to see use existing tools that provide the same thing, type either of the following from a command prompt:
route print
(This will dump the routing table)
ipconfig /all
(this will show you the state of ALL adapters including the loopback)
Dunno exactly, you should at least specify your configuration, is it DHCP or static IP, or something else?
It's the loopback interface
Some broadcasting may be required. ARP is the link-layer protocol, so it can be used without the IP address to broadcast a link to find the devices and then to detect their address. Don't know about windows precisely, but on Unix an arping command is present for this.
How can I get all the IP addresses and associated host names in a LAN?
To get the list of interfaces and IP addresses, use getifaddrs().
Search for interfaces with ifa_addr->sa_family == AF_INET
The IP address is in sin_addr.s_addr.
You can then use gethostbyaddr() to look up the DNS name for that IP address.
Update:
It was pointed out to me that the OP was probably asking about discovering other hosts, rather than the addresses of interfaces on the local machine.
There is no reliable way to discover other machines on the local area network, but there are a couple of tricks.
Ping method: Use the ping utility (or a programatic equivalent) to ping the local broadcast address, then see who responds. The broadcast address can be found by listing the interfaces as shown above. I believe ICMP does not require root access under OSX. Note that many systems may have ICMP ping disabled or firewalled, so you will only get responses from the non-stealth ones.
ARP method: Check the system ARP cache to see what IP addresses have been recently active. This will only show systems which have broadcast packets on the same network segment in recent minutes.
Both methods can be blocked by firewalls, routers, and even switches, so the exact borders of the "LAN" can be pretty narrow. Both methods can be implemented programmatically, but it might be simpler and more portable to just call out to the command line ping or arp commands.