i have a measurement setup where i want to trigger an oscilloscope base on a network package arriving. I have good results for a few seconds but somewhere between 20s and 40s i get a wrong trigger. My research showed that this could come from the arp packages send from the device. I tried to disable the arp sending but then the whole network went down. Now i'm trying to find a solution where i change the rate at which the arp packets are send without success. So i'm asking you if you know a way to either disable or send as few arp request as possible.
For your information i'm working on a Linux machine. Any help would be appreciated.
I allready tried:
#ip link set arp off dev eth0 <--- results in network down
changing the values for:
/proc/sys/net/ipv4/neigh/default/gc_interval
/proc/sys/net/ipv4/neigh/default/gc_stale_time
/proc/sys/net/ipv4/route/gc_interval
/proc/sys/net/ipv4/route/gc_timeout
with no success
Thx draufunddran
TL;DR: Disabling ARP on your machine will eventually cause other nodes on the network to stop sending packets to your machine (that is why your network appears to go down).
If you want to completely disable ARP packets on your network, you will need to manually program ARP tables on other nodes on your LAN (subnet) so that they know how to map your host's IP to a MAC address to send to on the LAN. This is a difficult thing to do if even possible since some nodes on your network may not offer the ability to program their ARP tables manually.
Related
I have a server in AWS-East-1 (N. Virginia) and I am trying to ping www.binance.com whose server is located in AWS Tokyo.
Command: ping www.binance.com
I get ping times of 0.5ms which is not true. Possibly, the ping is returning from some nearby router and theoretically even at the speed of light, the return trip should take atleast 75ms.
How do I measure the correct ping latency from my Linux terminal?
Assuming you need to make this test to check performance of application or network.......
Maybe, you can use other approach:
curl -o /dev/null -s -w '%{time_connect}\n' https://www.binance.com
It will return the time_connect so maybe it can help you in your analysis.
I recommend you to measure a round trip delay. It is the delay between the time when your network node request packet is sent and a time when the response packet from remote server arrives back to you. It can be measured by the Wireshark network analyzer. It analyzes a real traffic. The results are more accurate then from the ICMP protocol (ping) tests.
Wireshark usage
Ensure you have not opened any connection to your destination server (e.g. www.binance.com). Check all tabs in your web browser(s).
Find out the IP address of your destination server: dig +short www.binance.com and note all found addresses.
Install the Wireshark application if it is not installed.
Start the Wireshark, select correct interface on which the network data will be captured and start the capturing.
Open the IP address of page you will measure e.g. 65.9.96.71 in the browser. Refresh the page. It is not problem if error is displayed in browser.
Stop the capturing in Wireshark.
Put a filter string to the display filter field of the Wireshark. (See below for filter examples.) Press Enter. Only packets which have selected IP address will be displayed.
Watch the packet times in second column. Calculate the delay between the request packet and the response one.
Wireshark display filters (each line is one example):
ip.addr==65.9.96.71
ip.addr==65.9.96.30 and tcp.port==80
ip.addr==65.9.96.30 and tcp.port==443
Note:
The Wireshark installation in Linux requires some special steps. Confirm you agree that the Wireshark can be used by all users in system. Add your user to the wireshark group and re-login to apply new user setting.
usermod -aG wireshark <your_user>
Additional information
You can trace the network path between your client and remote server by traceroute. It shows you what nodes (routers) are there.
Verify in which country the destination IP address is situated. Use some IP Whois web page to get details. https://ipwhois.io/
I'm working on Linux 4.13.x. And I'm considering to send a packet response in the kernel.
Consider an echo TCP or UDP server running in the userland and there is also another node running a TCP or UDP client. Clients are sending requests to the server. I want to send the packet response back to the client without any involvement of server application running at userspace.
Here is my thoughts about this problem:
I started thinking how it is possible and I come across to a solution like netfilter. If I can capture the packets in NF_INET_PRE_ROUTING and then try to swap the source and destination IP addresses of IP header and also swapping the ports in the TCP header, then according to this answers and this presumably modified packet should be forwarded to the originator throughout the routing system.
Actually, I tried this scenario and it seems it is not possible to do so from netfilter hooks, however, I'm not sure of it. I thought that it is not working since it has problem with checksums because I'm manipulating packets so I did another experiment to figure this issue out. I just change the packet data and everything worked well. I think checksums don't have any problem since they will be check at NIC while receiving and also same situation while sending so manipulation in between doesn't make anything wrong. I also activate the IPv4 forwarding at the server host(sysctl.config) still nothing changes.
I don't want to create new packet, I only want to alter this packet and send it back. There is another similar question which is creating another packet. Moreover, I'm just thinking why this scenario is not working? But based on the netfilter's architecture it should work.
Thank you
I am also working on this, actually kernel validate the source ip address after ip_rcv function in NF_HOOK which check the source ip address. So just try below command:-
sudo sysctl -w "net.ipv4.conf.all.rp_filter=0"
after doing this also disable your interface from which you send and receive packet just like below:-
sudo sysctl -w "net.ipv4.conf.enp2s0.rp_filter=0"
I have an application on my linux host that communicates via UDP to another machine via 10G ethernet. The machine on the other end does not respond to ARP requests. I am able to get it's MAC address through other means (a different interface, on
Is there a way to programmatically get this information into the arp table w/out privileged status?
I know I can on a command line issue "sudo arp -s 1.2.3.4 AA:BB:CC:DD:EE:FF" every time I power it up.
I know I can add "1.2.3.4 AA:BB:CC:DD:EE:FF" to etc/ethers
I know that as a priviledged usr/process I can issue an ioctl to SIOCSARP.
All of these mechanism's require sudo/root access. I read something about giving the application "CAP_NET_ADMIN" permissions.
I'm looking for this capability so that the end users don't need to do any of the above. It seems like, If I, w/out sudo/root, can open a socket that determines the need for this network information, there should be a way for me, w/out sudo/root, to provide it.
No, you can't edit ARP information as non-root. This makes sense, as otherwise malicious attacker would be able to modify ARP tables and completely disrupt network communication and compromise security.
The solution to your problem is to fix your network configuration.
In wireshark I can see Membership Query, general IGMPv2 requests coming over and over from 0.0.0.0 source which suggests ( according to RFC ) machine that hasn't received address yet. My question is how in Linux environment I can find such machine. This query triggers many answers and causes significant network communication slowdown.
When a machine is connected to a network for the first time, it will try to find the DHCP servers in order to get an IP address configuration. Untill then, as you already said, it has no IP address and the only identifier it has is it's MAC address, which is used to keep a comunication alive while it negotiates with the DHCP server (during this period it does not have an IP address until the very last).
Answering your question, you'd find the machine you are looking for making use of the MAC address. If you are on a small network, a manual check (ifconfig) will do it but, if you are on a big one, you better check the ARP table of your switch(es) to have a better idea where it could be.
I have a larger network about 1000 pcs on LAN
I need to know that what is the fastest way to discover nodes/ pc on lan for admin pruposes
Abdul Khaliq
You could try sending out a ping message but it's unlikely that all nodes will reply to it.
The most reliable way to detect nodes is to perform ARP requests. You'll need to control a node inside the LAN (ARP requests don't pass through routers).