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

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2answers
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Why ARP need ARP cross LAN request?

Why ARP need ARP cross LAN request? When I am reading a document: You see the host A(10.1.0.1/8) send ARP Request for 20.2.0.1/8's MAC address. In general, the ARP request is for MAC address in the ...
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2answers
27 views

Why would pfSense ignore arp requests?

I'm configuring pfSense 2.4.3p1 as a transparent firewall. It's running in virtual machine with two vtnet paravirtualized adapters: WAN (vtnet0) connected to a 'far-side' network containing the ...
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3answers
56 views

Why do clients request a MAC via ARP, if the router knows the local LAN's MAC addresses already?

If I have an infrastructure type network, why does a local PC send out an ARP request for a MAC? Doesn't the router know the MAC addresses already, since it is using at least Layer 2? Does it do ...
4
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3answers
60 views

How to prevent IP conflict when using VRRP

We are currently using VSRP (Layer2/3) where we have a single IP as the gateway per VLAN. We are considering moving to VRRP (Layer3) which requires 3 IPs, 1 virtual and 2 real ones. This means that ...
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1answer
72 views

Iterative queries of a default DNS server

I have just started to study networks and I have a confusion about what happens when a default DNS server does iterative queries to other DNS servers to resolve a name in an IP address. I am very ...
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1answer
25 views

Network interface issues an ARP request to get the MAC address of an actively used gateway

My network interface actively uses a gateway to send IP packets to other networks. There is already an ARP entry in the cache for the IP/MAC association for the gateway. Is it normal that my network ...
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0answers
69 views

Sophos UTM WAN interface doesn't respond to ARP requests

I've sent this very question to Sophos Support but I feel that asking here might increase my chances to get an answer. The short question is: what could be the reason for my Sophos UTM VM WAN ...
3
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2answers
67 views

How does the ARP table work in case of the Gateway Router?

Suppose I am a host, I understand how ARP works in case I address an IP within my subnet. For each IP address there is a corresponding MAC address, and the owner responds to my broadcast ARP query. ...
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0answers
37 views

Same mac addresses for all the IPs [closed]

So I'm on a public wifi network and I'm trying to do intrusive testing. The issue is that while doing arp scan all the IPs are returning the same mac addresse.
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1answer
86 views

What are the key advantages and disadvantages of NDP compared to ARP?

So why they didn't use ARP in IPv6? is there any real benefit of doing this? what are the key advantages and disadvantages of using NDP instead of ARP? (In overall network performance, Security and ...
1
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1answer
28 views

Why would my router send an ARP request about a device that's already listed in its ARP cache?

I checked my Ubiquiti EdgeRouterX's ARP table and my laptop IP and MAC address were there. I then checked the DHCP lease and my laptop's IP address doesn't expire until tomorrow. I then ran ...
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3answers
88 views

If there's no response to the ARP request, will the host send to its default gateway?

Host A and B are on the same subnet. A sends ARP request(s) asking for B's MAC. For whatever reason, B doesn't respond. Will A either: Give up -- it can't reach B Send the packet to the default ...
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3answers
111 views

How to tell which one is the source IP and MAC address of the data being received?

I have to work with an FPGA module already running a code written by someone else. I have no access to the FPGA code. Now the setup is something like this:- FPGA is connected to the pc via ethernet ...
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2answers
71 views

Router ARP Table

I have attached the topology, PC0 and PC1 are in same network (192.168.1.0/24) PC0 send packet PC1 directly after arp resolution. So why router arp table shows PC0 and PC1 mac address. (Although the ...
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1answer
84 views

Which MAC should be used: device MAC or Interface MAC?

My L3 switch has ~30 interfaces. If you look at the output below there are two MAC addresses showing in the results of the show interface command. The hardware address is the same for all interfaces. ...
5
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3answers
716 views

What are the reasons for seeing an incomplete ARP?

As was mentioned in this post: The reason for seeing an incomplete ARP is that "An ARP request was sent for that address, but the host with that address is not up and running on the LAN, so there is ...
2
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0answers
96 views

Cisco: Routing issue between LANs [closed]

We have a project to create 3 offices, which are 3 different LANs where the configuration should be as follows: Each Office should have 1 printer, where the office is able to print They should be ...
1
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2answers
199 views

Gratuitous arp and unicast flooding

we have few 100s of access switches connecting to a core 10k in IRF. Here all our access is pretty much dumb does only L2 job. So what happens now is unicast flooding, technically MAC ages out, ...
3
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1answer
59 views

Question about diagnosis of ARP spoofing

Hello, I'm studying link layer and ARP Spoofing. While I was searching ARP Spoofing on internet, I found that being attacked by ARP spoofing can be found by checking whether there are duplicate ...
2
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0answers
52 views

Brocade FastIron ignoring ARP cache settings

I have a Brocade FastIron FESX648 and I'm attempting to increase the ARP cache timeout on a port that is connected to an IXP. According to the Brocade docs, I can increase the timeout up to 4 hours ...
2
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2answers
329 views

Network Device sending ARP request (opcode 1) but with Source IP 0.0.0.0

Please help me to understand this behavior of one of my networking devices. It sends the ARP request broadcast with the source IP:0.0.0.0 . I am only aware about 0.0.0.0 being used in "ARP Probes" ...
4
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3answers
902 views

How will be the ARP Request (Unicast/Broadcast) if Subnet Mask is Unknown

Please help me with one doubt regarding ARP requests. Based on my understanding the subnet of an IP is identified by it's Subnet Mask so consider this scenario:- Suppose Device1 with IP- 30.129.33....
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1answer
83 views

How would you map a network at layer 2 without CDP or LLDP?

I'm on an ASA right now and can path my directly connected next hop devices via IP address, but I want to make sure there isn't a switch in between. Another related question, when I "show arp" it ...
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0answers
179 views

IP Glean rate limiter

I have two data centres connected via dark fibre DWDM with Nexus 7700's either side, between them running OTV. When I fail over an F5 LTM with about 3000 Virtual Servers on one DC to the other DC F5 ...
1
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2answers
94 views

Endpoint MAC address change detection [closed]

A question regarding a host behavior when gateway mac address has changed (although it deals with Windows, I think it's the best forum). Assuming a windows host sending trafic to a destination IP, ...
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2answers
50 views

How to debug an unstable connection in a P2P configuration

I have a setup where I have two computers connected to each other (C1 and C2). Both have a static IP and they know each others IP. C2 sends UDP packets to C1 and C1 receives and logs them. Seems ...
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3answers
163 views

Cannot Ping Linux PC through L2 Switch

I’m a little embarrassed to be asking this but here goes. In a training video for CCENT, I see a switch connected to 2 PCs that are pinging each other on the same subnet. I try to replicate the ...
3
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3answers
277 views

Can the Ethernet source, ARP request SHA, ARP reply THA differ? Also ARP request TPA, and ARP reply SPA?

Can the Ethernet source, ARP request SHA, ARP reply THA differ? I take it for granted, that ARP request SHA, and ARP reply THA are always the same. But I'm not sure about whether the Ethernet source ...
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2answers
146 views

Ping a host that is in the same LAN

I'm trying to understand how the use of switches and routers in the same network work. This is related to this other question of mine. Suppose we have this network (I know this may not be a realistic ...
1
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1answer
465 views

Do routers discard packets if they don't know where to forward them?

If a router receives a packet whose IP destination address is not in its routing table, I believe it will send it to its default port. Suppose that we erase that entry from the table. Now, I think ...
1
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1answer
45 views

Does other hosts “learn” mac-ip entries on broadcast

in this post Learn MAC addresses via replies to other hosts requests I see that if host A sends an ARP query about host B, host C that resides in the same LAN will not learn host B MAC address, but ...
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1answer
150 views

arp or proxy-arp causing high cpu

We have an issue on a Cisco A901-6CZ-F-A with high cpu caused by Arp requests coming on Vlan11 from our customer. We enabled 'debug arp' to try and diagnose, below is a small snippet. IP addresses ...
2
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2answers
97 views

Two routers, one modem, dual IPs, second address drops connection occasionally

We have two ER-X connected via an unmanaged switch to a Cisco DPC3010 modem. Each is assigned a static WAN IP in a different block: 174.79.186.x/27 and 98.187.238.x/27. Every once in a while (roughly ...
1
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1answer
91 views

Multiple odd entries in ARP table of switch

While checking the ARP table on my switches, I found many entries that shouldn't be there. Before going into further details, I would like to emphasize that I'm talking about the ARP table and not ...
0
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1answer
82 views

Why does the `HWaddress` field of my router as returned by `arp` not match the output of `ifconfig`?

I am a software engineer trying to learn about networking from Ben Eater's video series. By looking at my wifi connection info, I think I have learned that my router's IP address is 172.20.20.1. (...
2
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2answers
231 views

Router issued ARP requests Target MAC = Broadcast, Host issued ARP requests Target MAC = 0's?

Why does an ARP request from my Router have a Target MAC Address: Broadcast While Host issued ARP requests always have Target MAC Address: 00:00:00:00:00:00? Also, I periodically see ARP requests ...
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2answers
118 views

Random ARP requests from source IP of different/nonexisting network

I saw this in wireshark and it worries me a bit: My network is 192.168.178.0/24. I already tried to look up the vendor from the MAC, no results. Why does it lookup what seems to be random IPs and ...
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3answers
100 views

Weird results when pinging

I'm learning IP addressing and routing basics, but I'm facing a problem which I cannot understand, so i have the following structure: Well in this situation, a ping from 130.190.0.16 to 130.190.4.30 ...
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2answers
159 views

Does a router divide a LAN into two seperate LANs, or a single LAN with two subnets?

The figure below is part of a networking homework question. The question asks about the source/destination IP and MAC addresses of frames sent throughout the system. My question doesn't touch on that ...
1
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1answer
167 views

Why does the receiver of an ARP request updates its cache table

If a device A needs to send an IP datagram to device B and if the arp table of device A doesn't have an entry for the mac address of the device B. Device A will send an arp request packet and in ...
10
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1answer
2k views

Should ARP requests be VLAN tagged?

I'm wondering if the ARP requests should be tagged when being sent out of a VLAN tagged interface? It seems logical to me that the ARP request should be tagged, since it needs to travel all the ...
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2answers
483 views

Sending packet through LAN cable to another PC having ip of another network

What happens if, say PC A(192.168.2.2) tries to send a packet to PC B(10.0.2.3) connected through LAN(only 2 computers are connected in this case PC A and PC B) as there is no router or a switch ...
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0answers
75 views

add 2nd ip on linux box, juniper refuse to add to ARP

I have a juniper SRX340 running as default gateway, I have a linux server (virtual machine actually) running debian 8. juniper ip: 192.168.1.1 Debian ip: 192.168.1.101 (eth0) I would like to add ...
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0answers
264 views

Proxy ARP and ping not working

I am trying to ping the loopback interface on R1. The configuration of the two routers: R1 interface addressing: e0/0 --- 10.1.1.1/24 e0/1 --- 11.1.1.1/24 loopback0 --- 1.1.1.1/32 R2 interface ...
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2answers
2k views

How does ARP work between two routers?

When ARP is used by a host in a LAN, then it is broadcast because the host does not know where is the destination host, but a router knows which interface it must use to get to the next router. Then ...
3
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2answers
220 views

Dynamic ARP Inspection - Does it check port in the binding database?

It is mentioned that DAI check for correct IP/MAC combination using the DHCP binding database. It is also mentioned that DAI is turned on for an entire VLan and not on a per port basis. If PCA (macA,...
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0answers
77 views

Cisco Asr1001 not able to receive 2048 macs (arps) in a sub-interface

I´m Brasilian, so excuse me any gramar error. I have a cisco router ASR1001 (IOS XE Version: 03.08.01.S) and I need to connect it to a service provider running BGP ipv4. This service provider gave me ...
3
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1answer
2k views

Get MAC address of all devices (IP cameras) connected to switch

I am a beginner when it comes to networking, and I have done as much research as I can to try and figure this out on my own, but the more I read the more I realize I don't know. I work for a ...
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4answers
288 views

ARP Cache entries

Consider 2 PCs 01 and 02, where 01 is connected to a router R, which is in turn connected to a switch S, connected to 02: 01--R--S--02 I need to understand what would happen to ...
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3answers
219 views

Why do we have to connect through a default gateway in a LAN?

I'm a beginner in networking and I'm looking for answers for these questions: Why do we have to connect through a default gateway when we are connected to a LAN and want to connect to another devices ...