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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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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34 views

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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2answers
56 views

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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218 views

Arpping responding with Cisco ASA interface mac address and mac address of machine

For some reason our Cisco is responding to arp requests between machines on the same switch. It's not breaking anything but it is slowing initial connections. I've been making a lot of changes on the ...
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1answer
49 views

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 ...
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3answers
48 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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1answer
20 views

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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1answer
21 views

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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2answers
64 views

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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2answers
325 views

How can I match conditions when I show arp?

In my Cisco Router I check the arp: Router>show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 192.168.1.1 - 0001.42D2.AE01 ARPA ...
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1answer
1k 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 ...
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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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2answers
8k 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 ...
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3answers
467 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 ...
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616 views

How the broadcast MAC address accomplished?

The Layer 2 broadcast is the destination address of the Layer 2 package is FF-FF-FF-FF-FF-FF. I have a question about the broadcast MAC address. you see the ARP request, it send the destination MAC ...
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34 views

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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1answer
66 views

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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5k views

Why do we need MAC Address if we can uniquely identify each machine with an IP Address

I learnt that in ARP Protocol, to send a packet from one machine to another machine we need to know the MAC Address of the destination machine but since the destination has already been assigned a ...
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1answer
297 views

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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3answers
80 views

How are packets ( received from the server ) sent to the host from the gateway ( which is present in the host network )?

If the host is receiving packets from a server, these packets have a destination IP address of the host and it is first received by the gateway present in the host network. Now the gateway checks the ...
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2answers
64 views

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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ARP Table Entry [duplicate]

There are 2 devices - A & B in a LAN. They have no entries in their ARP cache. Device A sends an ARP request to know the MAC address of device B, considering that the ARP request does not have an ...
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2answers
88 views

Question on ARP

I'm not really sure if the IP-MAC addresses for the router get stored in the ARP cache of endhosts, hence the question.
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3answers
146 views

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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2answers
856 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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3answers
63k 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 ...
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1answer
40 views

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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43 views

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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83 views

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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92 views

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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1answer
37 views

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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1answer
30 views

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 ...
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1answer
307 views

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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1answer
421 views

ARP spoofing over WLAN

As I understand, in ARP spoofing (of any kind), there's a man in the middle that intercepts frames from a sender (Alice) by masquerading as a receiver (Bob) and passes this frame to the server by ...
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4answers
2k 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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3answers
884 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 ...
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2answers
66 views

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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1answer
31 views

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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22 views

MAC flooding for new host in L2 domain [duplicate]

This hypothetical network has one dumb L2 switch and two hosts A and B connected to it. CAM table entries on the switch are all populated and both hosts have ARP entries for each other. Now if a ...
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1answer
60 views

Broadcast ICMP and gratuitous ARP

When sending an ICMP broadcast, all nodes can respond. is it the case of the sender too? If it's the case then: Is it specified somewhere that the sender should respond with gratuitous ARP when the ...
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29k 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 ...
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2answers
79 views

Can a switch send a frame back to the source host because of a loop?

First, I understand how switches work when they receive a broadcast frame. They will record the source MAC address on the incoming port (put it in the CAM table) and then flood the broadcast frame out ...
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2answers
103 views

ARP-Request - Reply from the perspective of a router

Presume I have a route table with such entries: typedef struct route_table_entry { uint32_t prefix; uint32_t next_hop; uint32_t mask; int interface; } route_table_entry; I have a ...
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1answer
44 views

ARP protocol, how it should behave [closed]

I am trying to implement the ARP protocol by myself, but I'm not sure how it should behave, how I should craft an ARP request. How does it work and why it should work.. I tried to research this on ...
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1answer
118 views

Wireshark does not capture free arp packets (opcode2)

Wireshark does not capture free arp packets (opcode2). Only arp announcement packages (opcode1). While running wireshark on the windows 10 computer, I turned on the other computers, but wireshark does ...
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1answer
161 views

Getting lot of unwanted broadcasts on my network

I am pretty new in Networking (noob), while I was monitoring my network using Wireshark, and I found that there is a lot of broadcasts happening all over the network, broadcast on Local network ...
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51 views

Arp Protect in dynamic VLAN environment

I am using 802.1x authentication with dynamic Vlan assignment(CPPM). As you may know, when a user logges in to their computer, SW attaches the user port to related Vlan. Thinking the scenario in which ...
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1answer
59 views

How does the swtich know if a packet needs layer 2 switching or layer 3 routing?

I have a network topoloty as follows A --------- B --------- C /|\ /|\ /|\ / | \ / | \ / | \ A1 A2 A3 B1 B2 B3 C1 C2 C3 A, B, C are ...
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5answers
3k views

How does a host in one subnet know to forward the packet to the router MAC, when trying to send a packet to another subnet

I am trying to understand the ARP protocol and I could not understand the above. Consider the topology as follows: H1(1.1.1.1) - (1.1.1.0)R(2.2.2.0) - H2(2.2.2.2) My understanding is that if the ...
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4answers
149 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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