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 ...
- 8,107
26
votes
Accepted
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 ...
- 14.8k
17
votes
Accepted
Pinging broadcast address
Not all machines will answer a broadcast ping. (all broadcast -- 255.255.255.255, or subnet broadcast -- eg. x.x.x.255) Some see it as a "security feature", because one could spoof the origin to flood ...
- 31.5k
11
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 ...
- 98.3k
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 ...
- 16.1k
11
votes
Accepted
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'...
- 27.2k
9
votes
Accepted
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 ...
- 98.3k
8
votes
What are real life examples of broadcast and multicast?
Broadcasts are stopped at a layer-3 boundary (router). An example of a broadcast is an ARP request where a host is looking for the MAC address of the owner of an IP address. The host sends a broadcast ...
- 98.3k
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'...
- 181
8
votes
Accepted
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 ...
- 6,104
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 ...
- 98.3k
7
votes
Accepted
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 ...
- 950
7
votes
Accepted
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 ...
- 98.3k
7
votes
Accepted
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 ...
- 81.5k
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 ...
- 360
6
votes
Accepted
What is the difference between ff-ff-ff-ff-ff-ff (layer 2 broadcast) 255.255.255.255 (layer 3 limited broadcast)?
They are aimed at different network layers. Every layer-2 broadcast must be inspected and processed by every host to see if it should be passed up to layer-3. A layer-3 broadcast received by a host ...
- 98.3k
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 ...
- 98.3k
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 ...
- 13k
6
votes
Accepted
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 ...
- 98.3k
6
votes
Accepted
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 ...
- 98.3k
6
votes
Accepted
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 ...
- 98.3k
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 ...
- 19.4k
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 ...
- 81.5k
6
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-...
- 81.5k
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 ...
- 16.1k
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 ...
- 98.3k
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 ...
- 66.9k
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 ...
- 27.2k
5
votes
What is the difference between ff-ff-ff-ff-ff-ff (layer 2 broadcast) 255.255.255.255 (layer 3 limited broadcast)?
The layer 2 broadcast address ff:ff:ff:ff:ff:ff is used on ethernet frames and is supposedly broadcasted on all equipments.
255.255.255.255 is the layer 3 address that is used to adress the exact ...
- 656
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?
...
- 1,636
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