Questions tagged [broadcast]

For questions about broadcasting in computer networking. Use this tag when you are troubleshooting or configuring network devices in relation to broadcast.

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16
votes
4answers
5k views

Why is 10.1.255.255 an invalid broadcast address?

I’ve been following the CCENT official certification book(100-105) and came upon this question in the “do I know this already?” quiz. The books only covered /24 subnetting only so far. Which of the ...
14
votes
3answers
31k views

How broadcasting works on different networks?

I was reading DHCP ( RFC 2131 ), I have basic knowledge about Relay Agent and Broadcasting. But for Understanding DHCP in depth, I felt like I have to know Broadcasting and Relay Agent ( RFC 1542 ) in ...
12
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2answers
13k views

Technical difference between a Collision and Broadcast Domain

Many people new to networking wonder what the technical differences between a broadcast domain and a collision domain are. Specifically: What criteria is used to know the boundaries of a collision ...
10
votes
5answers
2k views

WHY and HOW do routers and vlans break broadcast domains?

Everybody says routers (and vlans) break broadcast domains, but nobody goes into WHY that is, it seems. What's the router logic? Say I have three routers on my lan, with one main router and the ...
9
votes
2answers
495 views

How to control unwanted UDP traffic (Broadcast & Multicast) on Cisco Router 2911?

Please suggest, we are getting UDP traffic either broadcast or multicast in router 2911 which cause 95%+ utilisation of the router. And we got error in link and business impact due to this. Company ...
7
votes
2answers
499 views

How is the Groupwise Transient Key used in WiFi networks?

In Wifi WPA, I understand that during association, a 802.11 client and AP negotiate a Pairwise Transient Key (PTK), using which the Groupwise Transient Key(GTK) is provided to the station. I ...
7
votes
2answers
7k 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?
7
votes
3answers
11k views

What is the difference between layer-2 and layer-3 broadcasts? Please explain with an example

What is the difference between broadcast addresses ff.ff.ff.ff.ff.ff (Layer 2) and 255.255.255.255 (Layer 3)?
6
votes
3answers
838 views

Why couldn't a nework address be used as as broadcast address as well?

I am taking a refresher on Networking and I found out that: Network address is an IP address with all 0s after the subnet mask Broadcast address is an IP address with all 1s after the subnet mask ...
6
votes
2answers
4k views

OSPF manual neighbor configuration requirement on NBMA network

Why are OSPF neighbors manually configured on NBMA networks even when you enabled it with the broadcast keyword in frame map statements? Example is NBMA point-to-multipoint access. Thanks.
6
votes
1answer
509 views

Spoofing Ethernet with Source as Broadcast

I was wondering the following: Assume I am attached to a switch with an Ethernet Cable and I try to spoof the source/origin MAC address of an Ethernet frame with FF:FF:FF:FF:FF:FF. How would it behave?...
6
votes
3answers
6k views

Wake on LAN across VLANs in IPv6 network

In IPv4, if I want to send a magic packet to a workstation in another VLAN, I enable directed broadcasts in the remote VLAN and send it to the VLAN's broadcast address. This works great. In IPv6, I ...
5
votes
3answers
4k views

Why do we use VLAN?

According to my understanding, the network switch will look out for the specific MAC address and then it will forward the frame so basically it doesn't broadcast the frames then why do we make VLANs? ...
5
votes
3answers
10k views

What is the difference between broadcasting and flooding?

In Open shortest path first routing algorithm, the information about connected links is "flooded" throughout the network. How is flooding different from broadcasting?
5
votes
1answer
6k views

When and where to use Spanning-Tree (Portfast)

The tl;dr, in which scenario (switch-to-host, or switch-to-switch) do I use spanning-tree portfast or spanning-tree ...? We had a catastrophic network outage today. My first question to my boss was "...
5
votes
2answers
491 views

Can a broadcast storm do physical damage to computers and networking hardware?

We had a broadcast storm that went undiagnosed for several hours. After the problem switch was unplugged and traffic returned to normal, we had a handful of machines and switches that were broken. On ...
5
votes
2answers
4k views

Does a switch MAC address table sync across all switches in the same VLAN?

Ok, I have read up about this 16K limit for the MAC address table, or better known as the CAM table, on certain switches. Lets say I have 14 different edge switches with that 16K limit, and I have ...
5
votes
2answers
3k views

How does router prevent Broadcast radiation

I just learned networking and according to a wiki article on broadcast radiation prevention, it says: Filtering broadcasts by Layer 3 equipment, typically routers (and even switches that employ ...
5
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2answers
2k views

How far is VLAN broadcast propagated?

I'm not 100% sure of the vocabulary, so please bear with me. Suppose I've set up some new VLANs to better divide my network logically. I have a 4507 as a core network switch with VLANs 1 and 10-19. ...
5
votes
1answer
135 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 ...
5
votes
1answer
774 views

How does exactly reverse-path broadcast work?

I am not sure if I can ask this question on this website, since this is my first question here and I am not familiar with the kind of questions that can be asked here, but it is about a routing ...
4
votes
1answer
16k views

How do VLANs affect the broadcast domain?

I'm repeating a "LAN Switching and Wireless" module in college and I'm looking over past exam papers in preparation for the repeat exam. One of the questions is What is a broadcast domain? Using an ...
4
votes
3answers
13k views

What are the reasons for not putting multiple subnets on the same VLAN?

I would like to know why we do not (and should not I guess) use 2 different networks on the same LAN/vLAN. From what I tried and understood : Host in network A (ex: 10.1.1.0/24) can talk to each ...
4
votes
1answer
14k views

RIP V2 multicasting looks as broadcasting at IP add 224.0.0.9

In RIPv1 the packets are broadcasted out all ports with dest. IP 255.255.255.255. In v2 they are multicasted with dest. IP 224.0.0.9. In Packet Tracer, this v2 packet is transmitted over all ...
3
votes
4answers
3k views

How does DHCP assign an IP address?

I understand that IP address is a unique address to identify a machine in a network. But for the first time when i Plug in say ethernet cable of a network to my PC's Ethernet Port, how the IP address ...
3
votes
3answers
6k views

What is the difference between ff-ff-ff-ff-ff-ff (layer 2 broadcast) 255.255.255.255 (layer 3 limited broadcast)?

Please explain the flow of traffic in each case.
3
votes
2answers
649 views

Can a large broadcast domain break accesspoints

I have a network with a large class B broadcast domain (172.16.0.0/18 - 172.16.192.0/18) with a single DHCP server. I have lots of L2 switches in this network but there is no VLAN configured. My ...
3
votes
3answers
12k views

What are real life examples of broadcast and multicast?

In broadcast routing, packets are sent to all nodes even if they do not want it. What is a real life example of "broadcast"? Almost everything I can think of, like GMail and YouTube, appears to be ...
3
votes
4answers
47k views

pinging broadcast address

Iam using linux.I read somewhere in the internet that pinging the 255.255.255.255 will ping everyone in the network segment. And it will return every ip addresses in that subnet. but when i tried ...
3
votes
1answer
2k views

Why are DHCP ACK and REQ messages broadcast in Link Layer?

When I look at the protocol, I see that DHCP Request and Acknowledgement are both broadcast in the link layer. However at that point, both sides actually know each other's MAC addresses. Why do they ...
3
votes
2answers
22k views

Why can't devices in different subnets talk with each other?

I know that the layer 2 doesn't understand IP, and the broadcast domain is same. Why can't devices talk, how does it happen?
3
votes
1answer
299 views

Must a broadcast request come from the same network?

I was reading about Smurf Attacks and how Smurf Amplifier Registry keeps track of servers used for amplifying the attack, then I wondered, can a request coming from anywhere broadcast it to all parts ...
3
votes
2answers
826 views

Does WiFi broadcast traffic from a station go through the access point?

Let's say I've got two devices connected to my Access Point, a laptop and a tablet. If the laptop sends unicast traffic to the tablet, I understand that it must go through the AP. However, how is ...
3
votes
1answer
2k views

Breaking broadcast domain through VLAN and Router

Why do we need to create VLANs to break a broadcast domain when the router can do the same? 1.Breaking broadcast domain through VLAN- Breaking broadcast domain through Router-
3
votes
2answers
2k views

Broadcasting traffic by 255.255.255.255 or by “subnet dot all ones”?

If a device wants to broadcast traffic does it send it to the "all ones" IP? (Which is 255.255.255.255)? Or does it send it to "the all ones of the subnet"? (For example if the subnet is 123.123.0.0/...
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 ...
3
votes
1answer
4k views

Why should one server repeatedly ARP for the same host?

I am trying to use Wireshark to find the root cause of a particularly slow network, and started by examining Broadcast traffic. Not only does Broadcast traffic represent over 25% of total traffic (at ...
3
votes
1answer
53 views

Ability to monitor all broadcast domains

Example: Network of company A has 5 VLANs: Accounting, IT, Guests, Servers, Board. All VLANs has DHCP servers enabled in their own VLANs. I am monitoring a single VLAN for DHCP packets by connecting ...
3
votes
1answer
729 views

What is WDS and how can it cause a broadcast storm?

Recently I was told that we leave WDS off ,whenever we can, where I work. It was explained to me that a broadcast storm is created when a routers' broadcast gets back to itself, perpetuates itself and ...
3
votes
1answer
5k views

Point-to-point vs unicast, and multiaccess vs multicast/broadcast?

From Tanenbaum's Computer Networks: Point-to-point links connect individual pairs of machines. To go from the source to the destination on a network made up of point-to-point links, short ...
3
votes
2answers
127 views

How does frequency-division multiplexing deal with overlaps?

As I understand it, FDM uses separate frequency for each channel, thus A will transmit data, for instance, every two seconds and B every three seconds. But, what will be delivered on the wire in the ...
3
votes
1answer
3k views

How to block broadcast packets EXITING a single switchport

I have a couple cheap external wireless APs that like to reboot themselves constantly if they get even a few broadcast packets (i am ~90% certain this is the cause, after some testing with wireshark ...
3
votes
1answer
235 views

broadcast packets snmp graph shape

I recently started using OpenNMS to monitor our LAN. I found this broadcast packets graph on several devices. I'm trying understand the consistency (shape) of these data. Most other graphs, for any ...
3
votes
1answer
357 views

Do you happen to know why this happened on my outside interface? (wrong subnet, proxy arp)

The OUTSIDE interface on my firewall appliance is assigned IP address .2 The router it's connected to (ISP) is .1 Keeping in mind Proxy ARP was turned on (don't recall doing that, but it was), I had ...
3
votes
4answers
2k views

Prevent network auto-discovery between members of VLAN

At our ISP's we use Huawei s5300 switches, and we want to upgrade our setup to accomplish the following: Place a number of different customers/users under same VLAN. Assign one static-public IP ...
2
votes
3answers
3k views

Is Ethernet a broadcast or point-to-point protocol?

Theoretically speaking, as far as I know Ethernet was developed to be used as a broadcasting protocol and technology. I guess nowadays it is not being used this way. Since ALL the examples I see refer ...
2
votes
3answers
166 views

Does a dial-up modem support multiple users?

Since I have never worked with a dial-up modem, I was wondering if it created an internet connection for only one user, a point-to-point connection, or if it also supported multiple users.
2
votes
3answers
5k views

Do routers forward broadcast traffic?

Consider a host on 10.0.0.0/24 sending a packet to 10.0.0.255 and 10.255.255.255. In the first case all hosts on his subnet should recieve the packets but would the entire network receive the packet ...
2
votes
2answers
605 views

Is the real broadcasting on internet possible

Am sorry if my question is silly. But I want to clear that i doesn't mean just playing audio or video from a remote server.I am asking about conventional broadcasting as exists in Television and Radio ...
2
votes
2answers
814 views

Arping for local broadcast address

Given the local IP-network 10.173.128.0/24 I am looking at a wireshark and there is an ARP for 10.173.128.255. Why would a network client ever ARP for a broadcast address? Does this indicate a ...