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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.

3
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1answer
57 views

How do ARP requests work

So I may have a stupid question that mainly comes from me getting weird results to say the least while experimenting. I'm a bit unsure how do ARP requests work. For example how can I arp my entire ...
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0answers
38 views

Is this wireshark capture showing any issue?

I used Wireshark to capture the packets bellow: ... 350 18.942762436 d0:07:ca:0b:63:0c -> Broadcast ARP 60 Who has 13.210.32.75? Tell 13.210.32.78 351 18.947224197 d0:07:ca:0b:63:0c -> ...
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2answers
58 views

Why can't we have duplicated IPs?

This may be a really dumb question, but I like to turn upside down what I already know sometimes, that way I can learn more. For example, given a network 192.168.0.0/24, I have a device inside with ...
0
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2answers
191 views

How can i monitor ARP packet on WiFi network?

I want to monitor packet in my network. It said that ARP packet request broadcasted all over network. But why i only see my arp request packet and reply packet to the gateway?
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0answers
11 views

Updating arp cache table with many hosts [duplicate]

I'm confused about the behaviors of arp reuqest. Assume that i have many hosts in my network and they are connected using switch. host A(sender) sends packet to host B(reciver) in the same network and ...
2
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2answers
158 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. ...
0
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1answer
23 views

ARP table updated when receive message

I'm studying networking and I have a question about when an ARP table should update. Consider this scenario: Host A has the MAC address of host B in its ARP table. Host B's ARP table is empty. ...
0
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1answer
31 views

ARP behaviors between hosts connected via switches

In a scenario like the following, where different hosts are connected via switches only, I'm not sure how the ARP packets will look like when A wants to send an IP packet to B. I assumed all the ...
4
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1answer
400 views

Why would a switch ever send an ARP request for a MAC address when it can just wait for the first packet to be received from a device?

I've been reading 'Windows Networking Fundamentals' and in that book it says that a switch can learn what MAC address is associated with a particular port when the connected device makes its first ...
0
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1answer
23 views

Sending Frames Among Routers needs MACs?

Following this discussion: ARP request outside of LAN; Target machine or router response? I'd like to understand if router 1 sends its frames to router 2 through the same ARP process as discussed ...
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0answers
51 views

Swapping routers resulting in ARP issues?

A day ago I tried to swap out a router with a Meraki MX-84 Gateway in order to test the Meraki's VPN functionality. I set the static IP configuration on the MX-84's Internet interface to be the same ...
1
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1answer
62 views

Is there a way to capture only gratuitous ARP's using tcpdump?

I'm trying to set up tcpdump to filter only gratuitous ARP's. I know that I need to search for packets with a host set to ff:ff:ff:ff:ff:ff. And I found the arp.opcode parameter, but I can't seem to ...
2
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1answer
30 views

Why the ARP packet contains values like “Physical Address length” etc?

From what i know,MAC addresses are made of 48 bits,while IPv4 addresses are 32 bits Why are there these header fields? Are there MAC addresses with more or less 48 bits?
2
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2answers
102 views

No route to host for IPs in same subnet being routed by bgp

I have set up BGP to do some custom routing for a subset of addresses in the range 192.168.1.0/24. I have verified that the BGP is working by testing ping/curl on a different host in a different ...
2
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2answers
718 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" ...
2
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1answer
54 views

Virtual IP failover issue with vmware exsi ip based hashing

We are deploying HA database cluster on exsi which based on virtual IP concept for failover. if One node fail reserved VIP will be assigned to another node we have two exsi nodes and two virtual ...
20
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3answers
53k 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 ...
0
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1answer
41 views

How can a Juniper Router update its arp table?

I know the ARP table is cached data. On Juniper, we can use show arp to query the arp table: admin@juniper> show arp | match "16.23.43.75" ac:1f:6b:90:d1:ca 16.23....
0
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1answer
71 views

On a 3560E Switch

** Attempting to view IP address of a Non-Cisco device connected to the switchport. Already entered show mac address-table int gi0/35. Got the mac, then tried the sho ip arp vlan 120 | include ...
0
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1answer
32 views

Whether the ARP table is based on IP or Interface?

Is the arp table based on IP or based on network interface? I have a VM, it has an Interface with 10.211.55.7, when I show the arp, it shows: I want to know if the ARP table data is divided by IP or ...
35
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3answers
104k views

How does gratuitous ARP work?

Does gratuitous ARP work like a normal ARP request? Why is gratuitous ARP used for HSRP?
0
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1answer
80 views

Arp Cache Timeout [closed]

I'm trying to poll the arp table from a backbone switch but i want to understand which records are up. I just want to know if there is a specific time for the switch to keep a record on the arp table ...
0
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0answers
44 views

Wireshark switch ping

I understand that a switch will broadcast to all ports if it doesn't have the destined destination in its mac address table but when I analysed a scenario in wireshark I got confused at what happened. ...
0
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1answer
21 views

How does a system know the local gateways MAC address for given IP address [duplicate]

Assuming you have the following network structure. Knowing the IP address of the WWW-Server, system A wants to send an IP packet. As I understand the destination MAC address has to be in the same ...
1
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1answer
47 views

switch wireshark arp

I connected 4 pcs to a switch, I used pc 1 to ping another pc(pc 3) and used wireshark on all the pc's. The one that sent the ping sent out an arp request and received 4 request and replies from the ...
2
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2answers
90 views

Please help me understand this simple arp request / reply - how does a router know an IP address without knowing the MAC address?

I am new to networking, I am using Wireshark on my home PC to learn about ARP. I understand that ARP is used to build the ARP cache, which correlates IP addresses to MAC addresses on a LAN. ARP ...
7
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4answers
1k views

Does every host on the LAN share the same ARP table, or do hosts keep them individually?

I'm just learning about ARP. I'm a little bit confused. My confusion is better explained in a scenario. Host A is communicating with Host B. Host A knows Host B's IP address, but not it's MAC address....
2
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2answers
70 views

How does a computer know IP address of a computer on another network

I was watching a video explaining ARP, which was explained really easily but I got confused when they said that Host A already knows Host D ip address which is on another network. Host A and B were ...
3
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1answer
175 views

MAC Table vs ARP

I understand that for a switch to learn a MAC address, if host A wanted to send data to Host B the switch learns host A MAC and places it in the MAC table. If it doesn't know where the MAC (for Host B)...
2
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4answers
980 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 ...
0
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0answers
16 views

ARP and OSI model layers [duplicate]

Is ARP Layer 3 or Layer 2 protocol? It is used to figure out destination MAC, which is a second layer address, however, it has the info about destination IP address, which is a third layer address, ...
2
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2answers
93 views

How does a router know the destination mac?

so if I send a packet from a host to another from the same network we know the mac address of both the source and destination. However if the receiver is in a remote network the destination mac ...
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2answers
27 views

What is the bridging decision when getting ARP request?

Setup: Assume I have 3 VMs. VM1 VM2 and VM3. VM2 has two interfaces, say eth1 and eth3. eth1 is connected to VM1 physically and eth3 to VM3. I create a bridge on VM2 using brctl with eth1 and eth3. ...
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2answers
80 views

Why we need ARP when each device has its own IP address?

I don't really understand Address Resolution Protocol (ARP). Why we need ARP when each device has its own IP address?
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2answers
462 views

Device need Telnet to configure, but no IP is assigned

I have a UPS device connected to a Juniper EX switch. According to the UPS device documentation the device used DHCP and BOOTP to obtain a IP. This is part of a management network which doesn't have a ...
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2answers
4k views

How do routers traverse packets to their destination?

Sorry in advance for such a noob set of questions. I understand that when set with the task of sending a packet to its destination, a computer first checks that the IP address of the destination is ...
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3answers
171 views

If ARP uses broadcast, can I find out MAC-Address AND IP with it?

I have a peripheral device, connected via Ethernet to my Ubuntu. I would like to find out its IP, and untofetunately no it is not cached in my ARP table. ARP broadcasts the messages to every ...
1
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1answer
159 views

How does ARP work on multilayer (Cisco) switches

I'm going to develop an example scenario here: There is a computer that is connected to an interface on the switch that has been assigned VLAN2 and another computer on an interface that has been ...
3
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1answer
192 views

Cisco ARP cache rewrites?

I know that the Cisco's default ARP entry expiration is 240 minutes, however how does the ARP table mechanism work when a different MAC address is seen using the same IP? In other words, if I move ...
3
votes
1answer
108 views

To what address does ARP reply in the presence of MAC masquerading

The ARP packet has a duplicate of the sender/destination hardware address. Theoretically, you could have a case where a device sent Layer2: From AA:BB:CC:DD:EE:FF To FF:FF:FF:FF:FF:FF Layer3: ARP ...
1
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1answer
3k 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 ...
10
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3answers
11k 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 ...
3
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3answers
264 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
31 views

How can subnets not fulfil symmetric property?

While studying Internet Protocol, I came upon the following example of two devices: Device A: IP address: 10.1.1.1 Subnet mask: 255.255.255.0 and Device B: IP address 10.1.1.200 Subnet mask 255....
4
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1answer
352 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 ...
1
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1answer
115 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 ...
4
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1answer
76 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 ...
2
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1answer
42 views

Do the intermediate nodes learn a MAC address in ARP?

my doubt is about the ARP protocol. I know the procedure: if a host wants to know the MAC address of another sends a broadcast frame and the destination answers with its MAC. However, if an ...
5
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1answer
1k views

Cisco HSRP CAM vs ARP timeout

Today we received email from our ISP saying they are performing maintenance on their network so if you have HSRP connectivity with them in that case you need to clear ARP table or reduce ARP timeout ...
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2answers
384 views

Why I can ping these subnets from a different subnet?

I wonder why I can ping 192.168.3.50 /27 and 192.168.3.70 /27 from 192.168.3.100 /24. Is is not supposed to be impossible? Thanks in advance for your help.