Questions tagged [arp]

For questions about Address Resolution Protocol (ARP). ARP resolves OSI layer-3 addresses to OSI layer-2 addresses.

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2
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1answer
434 views

VxLAN - mac table entries in a TOR switch

It is a basic question. Assume 2 physical machines in two different subnets. VxLAN is configured on 2 TOR switches housing these machines in different subnets in different racks. Host A IP: IP-A ...
2
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2answers
4k views

Do any switches respond to ARP requests for IPs which don't belong to them?

Consider the following scenario: Host B has IP 192.168.0.100 and host A has IP 192.168.0.110 and they are connected to a Layer 3 managed switch having IP 192.168.0.254 on a particular broadcast ...
2
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1answer
2k views

arp update not working as expected

I have a simple network setup as follows (both switches are layer 3, and switch 1 is also a router to reach outside network): I need to move an IP address from PC A to PC B (following a PC failure). ...
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1answer
134 views

ARP 101, Two Hosts Different Networks

I know this is a repeated question here, but I cant find any previous threads discussing the headers. Is my understanding of this correct? Here's the scenario. Two hosts on different networks ...
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0answers
385 views

Why would a default gateway send two ARP responses to one ARP request?

We have a Netscreen router as the default gateway. I have a windows 7 machine in the network. I deleted the ARP cache on this windows machine using the command "arp -d". As soon as I did that, there ...
4
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2answers
3k views

Wrong dynamic ARP entry - IP Address couldn't pinged

Situation: Our Stacked Switch (two WS-C2960X-48LPS-L - 15.2(2)E3 - 192.168.10.19 - VLAN 10) wont be reachable via ICMP or SNMP by the Cisco Prime Infrastructure (172.16.2.103 - VLAN1[nativ]) and back. ...
7
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1answer
8k views

ARP request unicast MAC?

I would like to ask, with ARP request I got to believe that the destination MAC address was in all situations a broadcast address. Yet I got across a wireshark capture: I just cannot understand the ...
2
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1answer
1k views

Switch learning MAC address of default router

I know that switches learn MAC addresses of connected devices on their own by ARP and ARP Reply messages. Can a newly started switch learn the MAC address of default router on its own by ARP, or do ...
5
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2answers
679 views

Learn MAC addresses via replies to other hosts requests

I have a question regarding ARP: If host A wants to send a message to host B and the ARP table of host A does not contain a MAC address for host B then he sends an ARP request and host B replies with ...
1
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1answer
3k views

arp-scan different subnet

I have a setup of two routers like this: internet ---- Router A ---- Router B -- Host A \ \ webserver Host B Webserver resides in a DMZ and ...
2
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2answers
3k views

Scan all ip address on a network ARP/Ping

I'm working on a program to discover all computer on a network. What is the best way to do that My network is 192.168.1.0 There are few machines on this network and i want to know their ips Should i ...
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1answer
161 views

ARP Network monitoring and debugging:

I am reading the RFC 826, however I am unable to get the context behind the Network monitoring and debugging section: Network monitoring and debugging: The above Address Resolution protocol ...
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2answers
4k views

Do broadcast (FF:FF:FF:FF:FF:FF) packets go through the router, or directly all computers on the subnet?

If you have the destination MAC address you need in your ARP cache, surely it shouldn't have to go through the router? Or is that the point - only the router can be sure to have all of its subnet's ...
2
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4answers
259 views

Allow necessary protocols to ping when configure firewall

I am configuring a firewall hardware, which is connected between my laptop and lab LAN (lab LAN is also connected to other computers as well as Internet). My objective is to allow the ping between my ...
5
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1answer
199 views

What happens at the hardware level of a router when a packet is received and eventually triggers a process like ARP?

Please let me know where the gaps in my understanding are. There are many gaps, so please do not hesitate to fill them in or correct them. To my knowledge, what happens on the hardware level when ...
6
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1answer
2k views

ARP Questions (Packet Types, Ethernet, Cache, Gratuitous)

Lately I have been doing some research on the Address Resolution Protocol, and even though I know the idea behind it I still have some questions. Q1: Are there more types of ARP messages that I am ...
4
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1answer
83 views

ARP Packet format question

I am unable to understand the meaning behind the following extract from the ARP RFC 826: For the 10Mbit Ethernet, the value in the protocol field (ar$pro) is taken from the set ether_type$. This ...
6
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3answers
3k views

Server link bond across 2 switches with LACP, inter-switch LAG dropping alternate pings?

I have a Debian Linux server with 4x 1Gb NICs, 2 onboard and 2 PCI. All NICs are configured into a single mode 4 LACP bonded interface: bond0 I have two switches: Cisco SG300-28 and Cisco SG300-10, to ...
2
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1answer
468 views

Wireshark and Scapy sniffs only ARP packets most of the times (and it's one packet in 3 minutes)

My problem is that Wireshark and Scapy sniffs only ARP packets (sometimes LMNRR or DHCP - 5 packets of those in like 20 minutes..). Basically Wireshark and Scapy sniffs 1 packet in like 1-3 minutes, ...
11
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3answers
19k views

Find MAC address of a remote computer using IP

Is there a way to find out a computer's MAC address if we know its IP address, assuming this computer is outside our LAN? I know we can easily get the physical address of a computer in our LAN using ...
4
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3answers
17k views

Is it possible to block ARP request?

Is it possible to block arp request? If yes, how? If I can block arp request, does it mean that other machines in same network cannot find my machine?
1
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1answer
1k views

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 ...
7
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3answers
2k views

IP Address vs MAC Address, how does that really work together illustration

My question is simple, i don't really know if I understand it so I'm asking. Why do we have both addresses, if we know the ip address of the target and source computer, why do we need some physical ...
1
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0answers
78 views

ARP poison on divided network (every PC in it's own subnet) [closed]

Let's say that we have a room with a router and 30 PC's plugged in. Every PC has it's own 'subnet'. If we check for available hosts via ettercap/wireshark (on any PC), it only discoveres two hosts: ...
3
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2answers
578 views

Should the source and destination protocol addresses be the same in an ARP reply packet?

I'm trying to understand the contents of an ARP packet and the request/reply exchange from a Data Communications textbook and one example just doesn't make sense to me. There is an example that ...
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2answers
8k views

Wireshark shows duplicate IP address detected

Wireshark shows that an IP address belongs to two different MAC addresses: wireshark I spoofed ARP, and I use VMware. How can I fix this? How is it possible that one IP address can belong to two ...
5
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5answers
387 views

What blocks a computer from another network in the same switch from answering an ARP request?

Let's suppose I have 3 computers A, B and C connected to the same switch with only the native VLAN active. A and B belong to the same network, let's say that their IP addresses are 192.168.1.1/24 for ...
3
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3answers
8k views

When does the three way handshake take place in relation to data flowing down the OSI stack?

I am very new to networking and I am currently trying to get my head around the order things happen in relation to the OSI stack. I know that the Transport layer takes the data stream and converts it ...
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2answers
1k views

Will arp poison attack work in the WAN

I know how arp poisoning works in the LAN environment and I know that routers also contains mac-address tables with the neighbouring router's mac-addresses, that means routers exchange arp frames. So ...
2
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3answers
2k views

Cisco ASA Possible arp issue?

I've changed our Watchguard XTM firewall for Cisco ASA 5508-x, all seems to be working but do have one problem though... The nat / pat connections from the outside stop working. We have a single ...
3
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4answers
16k views

when will an arp table be updated

Will a device's arp table be updated only upon receiving a reply from a previously sent out arp request, or will it be updated if the device receives a frame/packet ? e.g. A send a arp request to B B ...
3
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3answers
4k views

Where do the layers of the OSI Model operate in the operating system?

The OSI model describes them as layers. But where do these layers actually operate in the operating system? For example, where and what actually does TCP? All these layers are described as using ...
2
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1answer
263 views

third-party arp table empty after ping

I have a small LAN with three hosts A,B,C connected through a switch. If A pings B, then the arp tables of A and B get populated, as expected. But C's arp table remains empty, even though it receives ...
8
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3answers
3k views

Will Linux send the ARP gratuitous or ARP probe (defined in RFC 5227) [closed]

I did an experiment to check if Linux will send the gratuitous ARP or ARP probe before using the target IP. The experiment scenario is as follows: There are two Linux computers, both connected to ...
3
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2answers
2k views

How to interpret this `tcpdump` output

this tcpdump output is the result of sending a single ping package from host 1 to host 2 through a simple hub connection: root@mininet-vm:~# tcpdump -XX -n -i h2-eth0 tcpdump: verbose output ...
4
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1answer
7k views

Cisco ASA 5505 stop passing traffic randomly

I have a very strange issue with Cisco ASA 5505 started about week ago: ASA like a router with outside port to ISP, next port to DMZ and another one to inside network (contains about 50 hosts thru ...
3
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4answers
2k views

Inter-VLAN Routing and Proxy Arp

the network above shown has PC1(10.10.10.1) AND PC2(10.10.10.2) IN VLAN 10 10.10.10.0/24 AND PC3(20.20.20.3) and PC4(20.20.20.4) in VLAN 20 20.20.20.0/24 I have configured all the configuration ...
5
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2answers
10k views

Difference between proxy arp and default gateway

Firstly what I understand, Default Gateway--> When we set the default gateway in PC the network layer check the destination IP address and if it is not on same broadcast domain as the source IP ...
4
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3answers
885 views

What is the point of ARP?

I'm a complete beginner at networking, but if I've understood this correctly, the gist of ARP is: We want to use high level adresses to the highest degree possible but ultimately, we actually need ...
-1
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1answer
46 views

Are there router or other network settings that can prevent the setting of a static IP addresson a client PC

We need to set up an application that requires the client PC to have a static IP address. It was having trouble retaining the assigned IP address between reboots until we disabled Gratuitous ARP. We ...
0
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2answers
204 views

What are the dangers of placing multiple servers on a single VLAN with static ARP bindings?

We have a cabinet of dedicated servers with a Brocade FESX648-PREM switch at the top. We own all the hardware and all the MAC addresses are known to us. We also fully manage the servers so we retain ...
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0answers
276 views

Why does NMAp find disconnected devices?

I want to wake up and see the devices connected on my local network, using NMAP. So I execute this command : sudo nmap -sn -PU[7] -PE 10.11.204.1/24 (extract from the man page : sn: Ping Scan - ...
4
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1answer
15k views

What is first? ARP vs ICMP

I want to know what is first after STP. There are just three devices, switch and two hosts. A switch is not configurated and two hosts have each IP by static. Of course, two hosts are connected to ...
4
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1answer
920 views

arp Requests not Being Answered After Server Move

So we just went through a big server move for a client - a couple of EX4200 switches we had installed from before-hand are now freaking out - all lights blinking always. Using WireShark I found that ...
0
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1answer
142 views

ARP-cache table update

Do routers update the ARP entry in their ARP-cache table when receiving the gratuitous ARP request/reply from a neighbour host?
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3answers
2k views

Get details of device connected to a network

I am trying to detect if a netcam is connected to my network on an Android app. To do so, I have found that I need to ping every IP on the network in order to get the active devices or somehow send an ...
2
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2answers
1k views

ARP table is not updated with NMAP

Here is what I do and what happens : Let assume I have a device A with IP X.X.X.200 connected to the network I use Nmap to ping my local network, with the command "nmap --send-ip -sP 192.168.1.1/24" ...
5
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1answer
682 views

Pinging across different subnets? This shouldn't work but it does

I have two computers: PC1 and PC2. PC1 has an IP address of 10.0.0.1/30, and PC2 has an IP address of 10.0.0.6/30. They are connected directly to each other with a crossover cable. My understanding is ...
1
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2answers
546 views

Netgear switch required default gateway for point-to-point link [closed]

So, my Netgear switch died, and after factory resetting it, I noticed that I was unable to connect to it. The Netgear was configured for 192.168.0.239/24, and I configured my windows PC to 192.168.0....
3
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3answers
686 views

What does it mean when we say that a single host can have multiple IP addresses [duplicate]

Actually I'm doing an online course and in the Address Resolution Protocol video lecture, this statement is made in the following context. And here's what the instructor says: It needs to because ...

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