Address Resolution Protocol is a layer 2 networking protocol used for resolving layer 3 addresses (such as IP addresses) into layer 2 addresses (such as Ethernet MACs). It is used by network devices when communicating with devices on the same layer 2 network.

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Xen Server interference on ARP requests

I have a strange behaviour on my network as my unix-like hosts seem to have problems to reach the gateway. Digging into the network traffic via tcpdump, I've seen that two different hosts answer to ...
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TCP connection RST after FIN, ACK

I have a situation that would like to clarify with the experts here. I am no network expert so maybe it's normal, but i rather ask. We are trying to diagnose a problem between two servers, both are ...
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Firewall thinks ARP is being spoofed

My firewall log is filling with messages about a possible ARP spoofing attempt on my own LAN: 192.168.111.60 is a Synology RS815RP+ NAS on my LAN. 192.168.111.7 is a Lenovo EMC px4-300r NAS. Both ...
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When are STALE arp entries deleted? (When never used)

root@openwrt:~# ip -s -s -4 neigh show dev lan 10.64.42.121 lladdr b8:20:00:00:00:00 used 6387/6341/6313 probes 1 STALE 10.64.42.157 lladdr b8:20:00:00:00:00 used 24/813/19 probes 1 STALE 10.64.42.12 ...
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Client doing ARP-requests on IP-Range

Today I faced the problem that our LAN (1 Server, 5 Client-PCs and several WiFi-stuff) went completely unstable. I tried to ping our router and server from my client and I had a lot of time-outs. I ...
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Cisco WAP321 dropping ARP packets

At my office we have 4 WAP321 connected directly to a Cisco 891f router. Randomly throughout the day, computers will lose access to the network. They will remain connected to the Wifi SSID, but can't ...
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26 views

Understanding arp request tcpdump

I noticed the below tcp dump when pinging a docker container B on bridge B from a docker container A on bridge A. Container A: 10.0.0.3 / 02:42:0a:00:00:03 Container B: 10.0.0.4 / ...
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Frequent unicast ARP requests

Wireshark screen I would like to ask if it's considered to be a normal behavior of a router to issue this many (as shown in the screenshot) "refreshing" arp request? As I do not see, for instance, my ...
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Juniper EX3200 connected to Cisco 2900 series router - incomplete ARP entry

I'm tying to connect a Call Manager Express running on a Cisco 2900 series router to a Juniper EX3200 switch. I have both configured on VLAN 4, with both ports in access mode but when I connect the ...
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What is the difference between arp_ignore and arp_filter?

What is the exact difference between the arp_ignore flag and the arp_filter flag defined in syctl.conf in Linux? Both seems to serve the same purpose.
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Strange linux neighbor cache entries (whole-world-is-link-local syndrome) (linux 3.0.0-16)

On absolutely standard ubuntu-server linux distro running only BIND cache, sometimes i see non-link-local ip addresses in the arp/nei table and there is no way to communicate with those entries After ...
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Make Linux reply to certain ARP requsts

I’m trying to pull a certain routing stunt where I want my Linux server to respond to arp requests for 10.0.0.1 on eth0, although 10.0.0.1 is not the configured IP for eth0 (in which case the ...
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Is there any way to ARP ping on Windows?

On Linux and other systems, there is an utility called arping which can be used to send ARP requests ("pings") and show the answers, much like the "ping" utility but using ARP instead of ICMP. Is ...
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How to reverse arp using nping for Windows

I would like to send a reverse ARP to resolve an IP address given a MAC address using nping for Windows. The documentation is not clear on how this should work and I'm unable to find any examples ...
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Linux is sending ARP requests to hosts in other subnets?

Setup Host B <--> Router <--> Host A Host A: IP = 192.168.1.10, Net = 192.168.1.0/24, VLAN = 1, Default GW = 192.168.1.1 (Router) Host B: IP = 192.168.2.10, Net = 192.168.2.0/24, VLAN ...
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Ping problems with two interfaces, same subnet, direct connections to two separate hosts

I have a configuration of a client machine (Ubuntu 14.04.2 LTS) that directly connects to two server machines. The server machines--while on the same subnet--cannot route to each other. Packets must ...
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iwconfig and arp commands report slightly different MAC addresses

I'm at a wifi hotspot where, when I look up the router's MAC address by two different methods, I get slightly different results: $ arp -a ? (10.128.128.128) at 00:18:0a:58:WX:YZ [ether] on wlan0 ? ...
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33 views

arpwatch to listen only to particular network

I deploy arpwatch is our network and it is working fine. But it is not doing exactly what i need. Here is what i need ... i want it to listen to one particular network ... for example on ethernet 0 it ...
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1answer
30 views

sudden increase in arp entries when i rlogin from one node to another node

when I r-login from my one host to another, I am observing sudden increase in arp entries from 80 to 900. and this is causing neighbour table overflow. can anyone suggest why this is happening?? ...
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Default gateway and ARP confusion

I have the following configuration (I'd post a pic but not enough rep for more than 2): PC1 (10.0.2.10/24) and PC2 (10.0.2.137/29) are connected to a hub, which is connected to a router on interface ...
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arp --delete is not deleting an entry; merely marks entry as “incomplete”

$ sudo arp -avn ? (10.10.7.30) at 00:cc:cc:bb:dd:86 [ether] on eth0 Entries: 1 Skipped: 0 Found: 9 $ sudo arp -d 10.10.7.30 $ sudo arp -avn ? (10.10.7.30) at <incomplete> [ether] on eth0 I ...
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1answer
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nmap and arp-scan inconsistent IP-MAC results

I seem to get variable and inconsistent results for the IP/MAC addresses from a particular machine, using nmap or arp-scan. The machine has 3 interfaces, and this is what it shows: $ uname -a Linux ...
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ARP cache getting null mac over a bridge

I have an interface eno1 and a bridge br0 $ ifconfig br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.168.250.53 netmask 255.255.255.0 broadcast 192.168.250.255 ...
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73 views

First ping (to any destination) fails from switch but not from router

I've got a basic network setup, just doing NAT to a single public address to an internal /24 without any VLAN's or fancy routing. Both my router and switch are running Cisco IOS 12.x. My ...
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432 views

Scanning network devices by mac address

I work in the security devices industry and most of my work relates to IP cameras. Each camera manufacturer has their own software that scans the network for their cameras and gives details about ...
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Obtain MAC address of remote, unconfigured device?

I have a device that goes on the network. I need it's MAC address. There is no label on it. How do I do that? I have no access to the device itself. I can power it on and plug it in to a switch ...
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ESX 6 arp fails in back 2 back link

we are having a strange problem with back 2 back connection between an ESX 6 and CentOS 7 machine. Hoping to find a solution on stackoverflow The story is below: - we are using a CentOS 7 directly ...
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4answers
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What happens when ARP Request comes from a different subnet?

What will happen when an ARP Request packet is sent from router1 to router2 in the following two cases? Will an ARP Reply be generated or the ARP Request packet be dropped? ...
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ARP broadcast flooding network and high cpu usage

Hoping someone here might have some insight to the issue we are facing. Currently we have Cisco TAC looking at the case but they are struggling to find the root cause. Although the title mentions ARP ...
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ARP behavior in Linux

I have a L3 switch. Port 1 and port 2 of the switch are added to VLAN 30 and an IP address (30.0.0.1) is assigned to it. Port1 and port2 are connected to Host1 and Host2 respectively. Host 1 and ...
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Cannot ping gateway

I replaced my aging fileserver with a new server running ESXi 5.1 and migrated my fileserver in a virtual machine running on it. Now I have the following problem with this VM: I'm getting the ...
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Xen networking - dom0 receives ARP requests but no reachability

Both dom0 and domU are Debian 8. Dom0 network configuration is: auto xenbr0 iface xenbr0 inet manual bridge_ports eth1 bridge_stp off bridge_waitport 0 bridge_fd 0 auto xenbr0.4 ...
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Dynamic ARP Entries turning into Static ARP entries

I recently acquired a client that has a strange ARP caching issue on one of thier servers. I have a server that will eventually start turning it's dynamic ARP entries into static ARP entries. This ...
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49 views

Cisco IPv6 Proxy-arp like IPv4

Can I disable the proxy-arp in IPv6 in Cisco? I cannot find the "no ipv6 proxy-arp" command in my Cisco router. Please teach me how to do it. Thanks.
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Windows 10 arp cache getting stuck after failed attempts when target machines are offline

After upgrading our development team to Windows 10 from 7, we are experiencing an issue with the ARP cache where a machine has the correct IP-MAC mapping cached, but the type is invalid due to failed ...
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Cisco 2960X & IPDT

I am interested in finding the IP addresses assigned to devices attached to each interface on a Cisco 2960X switch. It seems like IPDT is exactly what I'm looking for. However it seems like the ...
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ARP Request Being Sent To Different Subnet From Ubuntu Linux

This question is very similar to this one: Linux is sending ARP requests to hosts in other subnets? Main problem - Ubuntu Linux server is sending ARP requests asking for a MAC address of a host on a ...
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Ubuntu - Destination Host Unreachable Through Router / ARP Requests

Very strange issues on an Ubuntu server running DNS. Here is the network setup. There are two class C network ranges. Let's say they are: 216.107.249.0/24 216.107.250.0/24 Server is assigned an ...
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ARP issuse in SUSE Linux

I am dealing with a very strange problem. I have a VM running SLES 11 SP4 in VMware Environment. The machine has two NIC. All of a sudden the second NIC stopped working. It's not even pinging the ...
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Not sending an ARP request to avoid IP conflict

I am working on Ubuntu. I am setting a static IPv4 for my wireless interface (ifconfig wlan0 192.168.1.2) and connecting to a Wireless Access point and pinging it. I don't see in the sniffer that ...
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No answer on arp requests?

I have a problem where my Layer 3 Dell PowerConnect 6248 Switch (main switch) will sometimes (that means sometimes it works, sometimes it won't) not get an arp response from a device behind Dell ...
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147 views

http cookie contains datr not working (none packets is returned) wireshark

When I filter in wireshark: http.cookie contains datr none packets is returned, the list in null. What's I going wrong?
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How to make a simple network bridge in Vagrant?

I'm trying do set up the most basic network bridge demo in Vagrant. I have two machines in the same subnet, but on different LANs, and a bridge machine with two interfaces and a network bridge that ...
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Ettercap - packet injection / alteration

So I have a proxy setup using squid on port 3128. I also have ettercap setup. My main goal is to change data as it flows through my proxy. Basically, you open up www.something.com using my ...
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Accessing a server with wrong IP out of segment range

I have run into a similar problem as in this question about a wrong IP in LAN. However, the standard addr alias trick on the NIC did not help. I have no direct access to the server console, I might ...
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(solved -> bug) forward arp packets as vlan tagged arp packets

How can i forward arp packets as vlan tagged arp packets? e.g. arp packet (no vlan tag) -> eth1 -> eth2.1 -> arp packet (with vlan tag) With the following setup, the outgoing arp packets (on eth2.1) ...
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Arp reply on behalf of another devices on Linux

There are devices on a network that don't support ARP (let's name them NARPs) and a device that supports ARP, running Linux (lets' name it LX). LX knows the IP and MAC addresses of NARPs. What is ...
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why iptables SNAT doesn't help to answer ARP on the vlan tagged subnet?

I'm using iptables SNAT to setup a "router" on a linux box, it suppose to do NAT for 2 subnets. one untagged subnet 10.0.10.0/24, the other one is vlan tagged subnet 172.16.0.0/24. both subnet come ...
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149 views

ebtables arp filtering with openvpn tap interface

I want to prevent arp traffic not destined for the remote side going through a openvpn tunnel so I filter arp requests going to none of my own IPs. Server Setup: /etc/network/interfaces auto br0 ...
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Ping is happening but arp is not resolved

I am seeing one interesting problem. I have setup two devices connected through lan cable over eth3 interface. Now a vlan session has been created on both the interfaces. Device 2: root@10:~ ...