40 votes
Accepted

Why is 10.1.255.255 an invalid broadcast address?

I believe the book wrongly assumes network classes are still in effect. So a) would be a "Class A" network, where 10.255.255.255 would be the broadcast address. Another hint: There is no explicit ...
Sebastian Wiesinger's user avatar
26 votes
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WHY and HOW do routers and vlans break broadcast domains?

Let's talk about it using this topology of three networks (red / orange / blue): A Router's primary function is to facilitate communication between IP networks. Which means if A wants to speak to D ...
Eddie's user avatar
  • 15k
12 votes
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What is the difference between broadcasting and flooding?

Broadcasting is a term that is used on a broadcast domain, which is bounded by layer-3 (routers). Broadcasts are sent to a special broadcast address, both for layer-2 and layer-3. A broadcast cannot ...
Ron Maupin's user avatar
  • 99.4k
11 votes
Accepted

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

What is the point of reserving two IP addresses in a subnet when one might suffice? [...] If it's theoretically possible, why is it avoided? We live with our history. The distinction between address ...
jonathanjo's user avatar
  • 16.2k
11 votes
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How is the Groupwise Transient Key used in WiFi networks?

Why then does the client need to encrypt the broadcast using the GTK? It doesn't. Since the AP broadcasts, not the client, the client doesn't use the GTK to encrypt the frame. The AP does. Why can'...
YLearn's user avatar
  • 27.3k
9 votes
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What is the difference between layer-2 and layer-3 broadcasts? Please explain with an example

You need to understand the difference between layer-2 and layer-3 for an answer to have any real meaning for you, and I suspect you don't. A layer-2 network is a LAN, and all hosts on it are peers. A ...
Ron Maupin's user avatar
  • 99.4k
8 votes

What is the difference between broadcasting and flooding?

I will explain here in the context of switches (layer 2). Flooding When a switch receives a unicast frame (a frame with a specific MAC address intended for a particular device), it looks for the frame'...
Siva Prakash's user avatar
8 votes
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When and where to use Spanning-Tree (Portfast)

Spanning tree only runs between switches, never to standard end hosts. Bear in mind that, under normal circumstances, a port supporting spanning tree will (when it first comes up) run through a ...
rnxrx's user avatar
  • 6,114
7 votes

Why do we use VLAN?

Besides the unknown unicast flooding that you allude to, broadcasts are necessary to the operation of ethernet. Some protocols require broadcasts. For instance, hosts use ARP requests (broadcasts) to ...
Ron Maupin's user avatar
  • 99.4k
7 votes
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What are the reasons for not putting multiple subnets on the same VLAN?

There's really no reason not to put multiple subnets on the same VLAN, but there's also probably no reason to do it. Pro: Allows the subnets to talk directly without a router or firewall Save's ...
Dave Noonan's user avatar
7 votes
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Broadcasting traffic by 255.255.255.255 or by "subnet dot all ones"?

An application can send broadcasts to either the network broadcast address (network all ones) or the limited broadcast address (all ones address). It used to be the default for routers to allow ...
Ron Maupin's user avatar
  • 99.4k
7 votes

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

Initially, Ethernet was based on broadcasting physical layer technology (bus network for 10BASE5/10BASE2 or with repeaters), but logically (layer 2), the protocol has always been MAC-based many-to-...
Zac67's user avatar
  • 83.9k
7 votes
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Do routers forward broadcast traffic?

IPv4 uses limited broadcasts (to 255.255.255.255) and directed broadcasts (to the subnet address with all host bits set to 1, e.g. 10.0.0.255 for the 10.0.0.0/24 subnet). Limited broadcasts are ...
Zac67's user avatar
  • 83.9k
7 votes

Why is 10.1.255.255 an invalid broadcast address?

This is a "traditional" exam. question which contains: Missing information A trap A hint The missing information is the subnet mask or CIDR number of bits. The trap is answer (a) : 10.1.255.255/16 ...
grahamj42's user avatar
  • 360
6 votes

Must a broadcast request come from the same network?

Broadcasts do not normally cross layer-3 (routers). Some routers can be configured to forward subnet broadcasts, but the limited broadcast (255.255.255.255) will not cross layer-3. The Cisco version ...
Ron Maupin's user avatar
  • 99.4k
6 votes
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Is the real broadcasting on internet possible

I don't think you really understand that the Internet is just a collection of many ISPs which connect to other ISPs. Each ISP has its own policies. Also, IP has a single source and a single ...
Ron Maupin's user avatar
  • 99.4k
6 votes

Why do we use VLAN?

There can be many reasons to split a network into VLANs. Security seggregation. You may want to filter or forbid communication between some systems on your networks. Limiting of broadcast (and ...
Peter Green's user avatar
  • 13.3k
6 votes
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Does a switch MAC address table sync across all switches in the same VLAN?

Synchronizing MAC address tables across switches doesn't make any sense. Each switch maintains its own MAC address table. For instance, suppose you have Switch 1 and Switch 2 connected together of ...
Ron Maupin's user avatar
  • 99.4k
6 votes
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Why does OSPF use flooding instead of broadcasting?

You are confusing the layer-2 flooding with OSPF flooding. The routers in an OSPF area may not all be directly connected, but every router in the area needs to have a full understanding of all the ...
Ron Maupin's user avatar
  • 99.4k
6 votes

Can a large broadcast domain break accesspoints

First, please forget about classfull networks, they are dead for decades now. Having a /18 network is not recommended at all. As you pointed out, it is a very large broadcast domain that will cripple ...
JFL's user avatar
  • 19.6k
6 votes
Accepted

Does a dial-up modem support multiple users?

Almost all consumer Internet access links use only a single IP address and many business links as well. A single IP address can't be shared directly but extremely commonly (source) NAT is used. A ...
Zac67's user avatar
  • 83.9k
6 votes
Accepted

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

From RFC 2131 "Dynamic Host Configuration Protocol" Remembering that there can be multiple DHCP servers, the DHCPREQUEST is broadcast because: Those servers not selected by the DHCPREQUEST ...
jonathanjo's user avatar
  • 16.2k
6 votes
Accepted

Defining what type of casting based on IPv4 address

For IPv4, unicast addresses are in the 0.0.0.0 to 223.255.255.255 range*, multicast addresses are in 224.0.0.0 to 239.255.255.255 address range. *Broadcast addresses are more complicated. There is ...
Ron Maupin's user avatar
  • 99.4k
6 votes
Accepted

Flooding vs Unknown Unicast Flooding

As @ronmaupin points out, "flooding" is a generic term for sending data everywhere (usually except the source). OSPF multicasts link state advertisements, and we colloquially say OSPF floods them in ...
Ron Trunk's user avatar
  • 67.3k
5 votes
Accepted

What is the difference between MAC and İP broadcast addresses?

Remember, IPv4 is not the only layer-3 protocol. Traffic on a LAN is delivered by a layer-2 protocol, so layer-2 protocols need a broadcast address to be able to deliver a broadcast to all hosts on a ...
Ron Maupin's user avatar
  • 99.4k
5 votes
Accepted

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? ...
Everton's user avatar
  • 1,636
5 votes
Accepted

Spoofing Ethernet with Source as Broadcast

Q1: Would the switch drop this packet? Or do switches in general only look at the destination address? This would depend on the particular switch's behavior. Different switches will behave ...
YLearn's user avatar
  • 27.3k
5 votes
Accepted

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

I don't think this is possible. A broadcast storm from a bridge loop will effectively bring down much/all of your network (depending on bandwidth) but doing some permanent damage to the hardware is ...
Zac67's user avatar
  • 83.9k
5 votes

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

Ethernet was developed to be used as a broadcasting protocol and technology. That is incorrect. Ethernet was developed for a shared access media -- originally, a physical bus that ran throughout ...
Ron Trunk's user avatar
  • 67.3k

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