Questions tagged [arp]

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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Ubuntu Linux - multiple NICs, same LAN... ARP responses always go out a single NIC

We've got AT&T U-Verse internet service, which has an extremely boneheaded DSL gateway. We have 5 IPs (netmask 248), but the gateway is incapable of doing anything other than a single IP -> ...
darron's user avatar
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25 votes
4 answers
125k views

How to broadcast ARP update to all neighbors in Linux?

Some clients in the subnet has cached the IP with old MAC address, I want them to update the new value by doing a ARP broadcast, is it possible in Linux?
Howard's user avatar
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10 votes
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Why does Linux answer to ARP on incorrect interfaces?

I have the following Linux networking setup: there is an eth10 network interface with the assigned address 10.11.0.1/24. Then there is a tap0 network interface with assigned dummy address 0.0.0.1/32 (...
juhist's user avatar
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0 votes
1 answer
5k views

Why is a ping response being sent to the wrong gateway?

In a previous question, I was trying to determine why my OpenVPN clients could not ping the server LAN, even though the server LAN could ping the clients. Having investigated this further, I ...
jonseymour's user avatar
45 votes
13 answers
425k views

How to get a list of all IP addresses (and ideally device names) on a LAN?

Our network gave an error that there was an IP address conflict and I'd like to find what all the device IP addresses are. (I've also had need of that before). (update/clarification:I'm looking for a ...
Clay Nichols's user avatar
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20 votes
5 answers
76k views

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 ...
Cold T's user avatar
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16 votes
6 answers
34k views

ARP replies contain wrong MAC address

I've got a robot running linux with wired and wireless adapters. When I boot up, it connects to the wireless fine. When I assign an IP to the wired (either statically or with DHCP), it looks like it ...
Jayen's user avatar
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13 votes
4 answers
79k views

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? [router1]Intf1(20.0.0.1/...
gsinha's user avatar
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13 votes
2 answers
45k views

Default arp cache timeout

I didn't found how check and change the default arp cache timeout on Linux. I using debian with kernel 3.x (but I supposed it same with older kernels)
Pol Hallen's user avatar
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11 votes
4 answers
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When do STALE arp entries become FAILED 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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11 votes
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How to find the process which causes the arp request?

When i run tcpdump in the gateway, i get a lot of arp requests originating from the gateway itself. I wonder know why this happens. How can i find the process that causes these arp requests? $ ...
Ping Yin's user avatar
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8 votes
6 answers
31k views

Is it possible to match an internal IP address to a switch port?

I'm trying to find a computer that has a certain IP address on our internal network. I have identified the computer name from DNS, but in this case it does not help me. Just wondering if I can ...
Brent 's user avatar
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7 votes
1 answer
2k views

Cannot ping B from A until B pings A

I have a server cluster all connected on a local network(all physical machines, not virtual). When trying to ping from Server A to B, I get a Desitination Host Unreachable. I can ping from B to A no ...
Eumcoz's user avatar
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6 votes
1 answer
6k views

Ubuntu Linux - two interfaces, same subnet, different vlan - MAC/ARP issues

I'm attempting to setup a server that needs to have interfaces on the same IP subnet, but different VLANs: eth1.102 Link encap:Ethernet HWaddr 00:50:56:b1:00:0f inet addr:10.1.1.6 ...
Andy Coates's user avatar
4 votes
2 answers
4k views

ARP responds with single MAC address on Linux server with multiple interfaces on the same network

Linux server has 2 active network interfaces: IF:eth1 IP:192.168.1.1/24 MAC:11:11:11:11:11:11 (1GbE) IF:eth2 IP:192.168.1.2/24 MAC:22:22:22:22:22:22 (10GbE) The idea is that the ...
sardean's user avatar
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4 votes
3 answers
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How to configure remote access to multiple subnets behind a SonicWALL NSA 2400

I have a client that uses a SonicWALL NSA 2400 as their firewall. I need to setup a second LAN subnet for a handful of PC. Management has decided that there should be a second subnet even though ...
Kyle Noland's user avatar
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3 votes
1 answer
2k views

Linux: What causes static ARP entries to flush on link down

This is a question about a difference in networking behavior between Debian Buster (kernel 4.19.0-18) and Debian Bullseye (kernel 5.10.0-9). On Buster, proxy arp entries survive if the link on the ...
roelvanmeer's user avatar
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2 votes
3 answers
6k views

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 = ...
Deputy Rock's user avatar
2 votes
1 answer
2k views

How to setup a static multicast ARP entry with Cisco SG300?

We're running a Microsoft NLB cluster in multicast mode as a loadbalancer. Using our old Cisco IOS switches we propagate access to the cluster to our branches using a static ARP entry in the core ...
Fredrik Hedberg's user avatar
2 votes
1 answer
3k views

Why does a PXE-booting VM aggressively seek Reverse ARP?

Reverse ARP is.. well, pretty much dead, as far as I'm aware? One of the great Internet success stories in killing off a protocol? It's been deprecated in favor of BOOTP (and later, DHCP) for almost ...
Shane Madden's user avatar
2 votes
3 answers
2k views

Best method and tools for local IP scanning [closed]

I’m starting to administer a small but confusing und badly documented local heterogeneous network (mostly Windows workstations, printers, laboratory equipment, etc. and one Linux/Samba Server) (192....
esc1729's user avatar
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2 votes
3 answers
2k views

arp table filling up

I have a CentOS 5 system which serves as an IPSec VPN connector between my network and a couple of remote networks. Lately it is running into this problem once or twice a day where its ARP cache gets ...
MK.'s user avatar
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1 vote
0 answers
558 views

MAC address in arp table doesn't match actual MAC, why?

If I connect my laptop directly to the config port of a ubnt airFiber radio I can set a static IP to my laptop and access the default config page to change settings on the radio. When I look at the ...
demiAdmin's user avatar
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1 vote
2 answers
3k views

wierd arp issue with 2 interafces sharing same subnet

I have two linux machines connected through a switch. bothe machines run linux RHEL 7.3 kernel 3.10.0-327.el7.x86_64 one of the machines is connected with both ports to the switch and the other with ...
user664174's user avatar
0 votes
3 answers
2k views

ARP broadcast and router performance

My employer subscribes to a fiber based leased Internet from a publicly owned incumbent ISP. The ISP admin says that he cannot give a subnet bigger than /30 because he fears that the ISP edge router ...
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