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Questions tagged [arp]

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

19
votes
3answers
51k views

How does a switch learn a switch table?

Say the switch table is empty. If computer A sends a frame destined to computer B, the switch will broadcast asking who has the mac address of B. What if C suddenly sends a frame to A? What is the ...
34
votes
3answers
101k views

How does gratuitous ARP work?

Does gratuitous ARP work like a normal ARP request? Why is gratuitous ARP used for HSRP?
17
votes
6answers
10k views

Best practice for the combination of HSRP and ECMP

The combination of ECMP (or other causes of asymmetric paths) and HSRP is broken by default in Cisco IOS; the default behaviour with this design floods unicast traffic excessively. What is the best-...
11
votes
3answers
31k views

On which layer of the OSI Model does the arp protocol belong? [closed]

Can anyone explain which layer of the OSI model ARP belongs to and which socket it uses? I referred to lots of books before asking this question. In some books, Authors are saying that it belongs to ...
13
votes
6answers
21k views

How are IP addresses mapped to MAC addresses?

I've been reading about the differences between MAC and IP addresses, and why we need both of them. To summarize, MAC addresses are physical unchangeable unique IDs for every single device while IP ...
6
votes
1answer
4k 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 ...
5
votes
1answer
825 views

Why are routers not answering ARP Broadcasts?

Host A wants to send something to Host B who is in a different network. Between them is Router 1. Host A sends an ARP broadcast but Router 1 is not answering it. Why is that so?
3
votes
2answers
575 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 ...
8
votes
1answer
2k views

Something is filling my force10 ARP table

I have 2 force10 s25 switches that are used for a dark fiber link between two school buildings. One of my switches is filling its ARP table to the brim and then failing. This can happen as often as ...
14
votes
5answers
9k views

Duplicate IP Address - which one wins?

If there's a duplicate IP address, which one "wins"? First, last, flaps, neither?
9
votes
2answers
2k views

Differences and functions of type codes 0800 and 0806

What are the primary differences and functions (or applications) of type codes 0800 and 0806? Through my own research, I found the 0800 was related to the 0800 to the IP/Layer 3 of the OSI model. ...
4
votes
1answer
331 views

ARP table aging: What timer can I expect?

Is the hold time standardized? Is there a standard or reliable recommendation for a timeout? I am well aware that a SOHO non-managed switch requires a shorter timer than a data-center switch. That ...
3
votes
3answers
450 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 ...
3
votes
2answers
3k 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
votes
4answers
5k 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 ...
6
votes
2answers
6k views

ARP Replies can they be Broadcast

I have been informed by certain networking professionals that ARP replies can and sometimes actually are broadcast packets instead of unicast. If and when would you use a broadcast ARP reply?
6
votes
2answers
590 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 ...
5
votes
2answers
9k 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 ...
5
votes
5answers
271 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 ...
5
votes
3answers
1k 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 ...
3
votes
1answer
487 views

ARP Destination address (internetwork)

Let's say i have the following WAN: Suppose that all arp tables are empty and that E wants to send a packet to A. The E will send an arp request with destination ip of Router 2(unicast), get its mac ...
3
votes
2answers
359 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,...
3
votes
1answer
4k views

What happens if two hosts with the same MAC address are in the same broadcast domain?

I am aware that situation, where duplicate MAC addresses appear in the same broadcast domain, should never happen. However, if such situation happens, then how will the network work? I think one ...
2
votes
3answers
166 views

Ping command through network

I have been trying to understand how and what tables are populated ( if they are clean at the start) when a ping command goes through. Lets say I have this network: I want to send a ping command from ...
2
votes
4answers
958 views

Should I receive an ARP reply from a host that is logically on a different subnet but is connected to my host via a hub?

Host A: 128.238.66.100/16 Host B: 128.238.67.100/24 The hosts are connected to the same hub and nothing else is connected to that hub. The routing and ARP tables of both hosts are empty. Host A ...
2
votes
2answers
1k 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 ...
2
votes
1answer
454 views

ping reply arp table

I have created a simple topology with routers and computers and I ping from computer A to computer B . Firstly, computer A send ARP request to gateway of A and then got reply. Mac and ip of gateway is ...
1
vote
3answers
375 views

ARP Table basics

I'm using the arp -a command to look at the ARP table on my personal computer. After executing the command it shows two types of addresses, dynamic and static. What do the dynamic and static types ...
1
vote
1answer
7k views

Why does it show ARPA incomplete?

r-tx-server-1#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.199.0.12 0 Incomplete ARPA Internet 10.199.0.53 0 ...
-1
votes
3answers
592 views

How do 2 PCs learn each other's IP addresses for ARP resolution? [closed]

So, if one PC will use another PC's IP address for ARP resolution, how does the PC sending the ARP Request even know which IP address to call for in the first place? What happens in a scenario where ...