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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What could be blocking ARP?

I have a metro ethernet link between two offices with Cisco C3560X's on each end. Actually, I have two links. (We are switching from one provider to another.) I can't get the new link to work. Pinging ...
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3 answers
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How does a router find the next hop when the receiver is in a distant IP network?

Say I want to send a frame to a web server, and let's say this web server is in a very distant IP outside my local network e.g. a Google server. I initially send the frame to my router. My router ...
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Will there be an ARP-Request to a gateway outside the subnet? [duplicate]

This is a question from an exam I don't know the answer to. A client has a wrong configuration: He thinks his only gateway is not in his own subnet and needs the MAC address of the gateway. Will he ...
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How router will send ARP resolve packet when it receive ARP request?

How router will send ARP resolve packet when it receive ARP request ?? Router by default enabled with proxy arp configuration?? If then proxy arp is not configured then what will happen if it receives ...
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How is the destination MAC address filled during MPLS label switching?

During IP packet forwarding, after a LPM(ip lookup) done on the FIB, it will fetch the Nexthop ip address and the egress interface to send out the packet. Now, ARP table lookup is done for this ...
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How does ARP work, when the host with known MAC address is moved to another subnet

I've been trying to figure out this for some time, but I'm quite lost. Assume you would have 3 networks -> A (PC0), B (PC1) and C How would ARP behave, if it already knew all MAC addresses from ...
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1 answer
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ARP cache in firewalls and difference from an end point device

Imagine a device A (192.168.32.5/24). Then two hosts, B and C, connected to the same interface (through a switch) having the same IP address (192.168.32.8/24) configured statically. No fancy tools/...
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ARP requests from a different subnet

Not sure if my question is on-topic here. I found the following question about ARP requests from a different subnet and I was wondering if and when this is an actual use case. The original question is ...
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How are IP broadcasts handled at lower levels

When I use a broadcast IP address, for example 198.255.255.255, what will happen when it gets passed down to the link-layer which will then look for the corresponding MAC address in your ARP table. ...
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Is the "ping" command a broadcast message?

I am learning about how ARP works and I have some questions regarding the ping network utility. ping is used to test connectivity and reachability between devices. PCs have their own ARP table where ...
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ARP Header's Mac Address set to 0 when broadcasting [duplicate]

I'm learning about Ethernet frames and networks and Wireshark has been very useful. I have a doubt regarding broadcasting and ARP request, since we don't know the Target MAC address, in the ARP's ...
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Can a host not send a response to an ARP request to remain hidden?

Let's say a malicious host connects to a network. It doesn't wish to identify itself to other devices on the network unless it wants to (eg: for a desired conversation). From what I understand, the ...
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Receiving ARP requests from different networks (cable Internet)

On the WAN interface I constantly receive ARP requests from many different networks. The source MAC address is always the same (MAC address vendor: Casa Systems Inc.). 22:57:57.032541 ... Request who-...
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How to learn IP addresses in a LAN

For communication with machines in the same LAN, hosts do ARP for translating the IP address to MAC address, which means, IP addresses are already known to each other. My question is, how does the ...
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The initial ARP cache for a router that never got a packet

I am trying to understand the ARP cache. So, here is the physical structure of my network: Note that I did not ping any of the PCs yet. So, I expected the ARP cache of the router R1 to be empty. The ...
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Why the two connected routers via PPP doesn't use ARP but ethernet use ARP?

I have read from @Ron Maupin's answer of this question that your two routers are connected via PPP (this is not uncommon), ARP will not be used , but if the two routers are connected via ethernet, ...
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Do hosts in the same LAN know their MAC addresses?

I am trying to learn about how ARP protocol works in LANs. So, here is the physical structure of my network: So, when I try to ping PC3 from PC1, I expected the first packet to timeout because PC1 at ...
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Is knowing MAC needed for talking to another device in same wifi network?

I have heard about ARP protocol for learning MAC address of other devices in a LAN for communicating with each other. However, I am bit confused about how it works in a typical infrastructure mode, ...
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Client's ARP requests affect whether Cisco C897VA receives packages or not

So I have bought used ISR C897VA with an issue: when vlan1 is pinged from windows there are quite a lot of "Request timed out"s. Config-register 0x2142 has been done, as well as resetting ...
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Question about ARP requests

When a device tries to associate an IP address with a MAC address for a given device, it sends ARP requests to all devices connected to the same network. If I understand correctly, the searching ...
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What does a router do with a packet if it can't find the destination IP address in its routing table?

If a router receives an ARP request in which the destination hardware address is a broadcast address, and if the destination IP address is an address that the router cannot find in its routing table. ...
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how does a host learn about other hosts IP addresses connected on the same subnet? [duplicate]

My question is similar to one posted [here][1] But answers are not understandable to me. How can a host (say my laptop) learn about IP addresses of other devices (say my phone) on the same subnet. ...
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1 answer
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ARP sending an ARP request on changing port IP address

Using the c7200 images on GNS3. I configured two routers as so: With arp debugging on, after assigning an ip address I see that each router sends a gratuitous ARP response packet (only debug output ...
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ARP isn't showing all the interfaces/MAC bindings

I'm playing with Dot1x port authentication, the interface G2/0/2 is connected to a PC and is authenticated/authorized successfully: SW1-2960#show authentication sessions int g2/0/2 det ...
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Why does ARP request not use a router instead of broadcast?

Why in ARP request does the source computer broadcast a message with the destination IP address to find the MAC address of the destination computer? Why doesn't it send the message to the default gate ...
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What if a host makes an ARP request for an IP outside its subnet?

I have read other similar question on the forum and none have completely answered my question. But to understand my confusion, you would need to know what else I'm confused about. Is ARP a layer-2 or ...
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Under what circumstances is the ARP table updated?

Lets say we have 3 devices in the same shared medium : A, B and C. A wants to send a message to B, so before, it sends an ARP request as a broadcast message. When B receives it, it will update its ARP ...
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Arp Access-List Without An Interface [duplicate]

I have dhcp snooping an arp inspection setup on my VLAN. I have a number of clients that need to be statically set on this VLAN but still plug into a DHCP access port on the VLAN. I have ip dhcp ...
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IP Snooping\ARP Inspection With Static Devices On DHCP VLAN

Consider this network: I have enabled DHCP snooping on my system. Switch A has the DHCP connected and the port on VLAN 70 for DHCP has been trusted to allow for reading the database and passing ...
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VPN with Cisco virtual ASA on Azure not routing correctly

I've deployed a Cisco virtual ASA in Azure to use as a VPN server. For simplicity, I'm using just the management interface as the lan for the time being (10.2.0.4 is the interface). I want to use the ...
1 vote
3 answers
132 views

Why do IP(v6) routes require a next hop IP(v6) address and not just a MAC Address?

My understanding of how you "ask" a router to route a packet for you is that you simply put the IP(v6) address of the destination host and the MAC address of the router you are routing via ...
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ip dhcp snooping Kills DHCP Ports

I am working on implementing DHCP Snooping on my switches and have found that when I do so it kills the DHCP connection to the clients. The network is as such: The server with DNS is providing DHCP ...
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Unable to Communicate from server to other servers after migrating from existing firewall to new firewall

In our existing environment we had migrated old firewall with new firewall after this activity . we had faced connectivity issue . From servers unable to reach other servers . Post clearing ARP table ...
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1 answer
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issue regarding broadcast mac address

I read a line saying {Routes do not forward packets coming from one interface having broadcast mac address (FF:FF:FF:FF:FF:FF)} what is meant by one interface in that line? if router cannot broadcast ...
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EVPN+VxLAN strange silent host issue

EVPN+VxLAN very strange silent host issue I have very basic EVPN+VxLAN design where i used OSPF/Multicast/BGP/vPC technologies to build small size datacenter. L2VNI working great without any issue. I ...
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Broadcast times for new devices in ARP protocol

How many broadcasts are needed in ARP protocol for one new device send to another new device to get necessary ARP table entries for lookup in one switch?
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Suspicious flood of ARP requests [closed]

I'm trying to review a Wireshark capture and it seems the network is heavily flooded with ARP requests that make no sense to me. The destination is not "Broadcast", but some unknown DELL ...
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2 answers
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What role is ARP playing for a internet request?

For me it is not clear how the internet is working. Let's say we have host (local IP:192.168.12) and the gateway/router (local IP: 192.168.0.1 / extern IP: 62.1.2.134) Now the client (192.168.0.12) ...
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1 answer
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How does router know MAC addresses of computers that are connected to a separate switch? [duplicate]

i am a newbie but i need to understand this ARP thing. In my company we have a router that has 3 switches connected to it. On the switches there are more than 100 hosts. I know that switch learns and ...
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Much ARP requests from Cisco ASA 5510

An employee of the ISP writes to me that a lot of ARP requests from us go to them. ISP equipment log: 07:47:27.732242 ARP, Request who-has AAA.BBB.CCC.213 tell AAA.BBB.CCC.53, length 46 07:47:27....
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How does the ARP table know to update if two hosts flop IP addreses?

When hosts on the same local network communicate, they manage their own ARP tables which translate between IP addresses and MAC addresses. Thus when computer A needs to send data to IP address ...
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ARP Router issue

I have a question when a Router receives ARP request to a host that dosen't exists on the forwarding table for that router does the. And this Router is not the next hop either will the Router continue ...
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Intermittent Network Performance Problems

I've been dealing with an intermittent issue in my network for several weeks now. Symptoms: Periodic "Destination host unreachable.", and similar errors when pinging. The following is ...
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IP datagram route through a network utilizing ARP

Suppose I want to send an IP datagram from node D to node C . Each step I also want to list the MAC addresses of the source and the destination , as well as the source and the destination of the IP ...
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How might ARP impact the UDP communication and what is a scenario i can reproduce to check/understand it?

I was wondering which impact the ARP protocoll might have on a UDP communication. I am learning for an exam and trying things out with mininet (linux )/ wireshark to understand the dependencys between ...
2 votes
1 answer
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How to capture mixture of packets with and without VLAN tag over LACP with tcpdump?

Given following configuration in Linux: bond0 in LACP (802.3ad) mode with two VLAN networks running over it. bond0.111 configured with static IP bond0.222 configured with DHCP How to capture packets ...
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Why is in all arp table snmp oids an interface index before the ip number?

When I want to get arp information about a single ip number or subnet, I have to snmpwalk the whole arp table, as some oid architects had the "great" idea to always insert an interface index ...
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2 answers
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When traffic is intiàted from pc is ANDing process or ARP process start working first

When traffic is initiated from desktop which process starts first; the ARP process or ANDing process?
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1 vote
2 answers
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Is the outgoing interface of a router in the same Subnet as the Incoming interface of the NEXT HOP router?

In the TCP/IP Volume 1, it is stated that ARP works only on the same subnet. Does this mean that the outgoing interface of a router is necessarily on the same subnet as the incoming interface of the ...
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Who can get ARP packets? [duplicate]

I'm new to networking. And as far as I understand about ARP messages, Alice can only send ARP to Bob if two are connected. But if Alice and Bob are connected to a router, but not connected to each ...
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