40

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 network size specified (/24, /27, ..) so it is implied you know about network classes. Classical example of outdated literature.


26

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 or B, the Router must be used. However, a Broadcast by definition is a message intended to be sent to everyone within the sender's local network. If Host A ...


15

Theory By convention, a collision domain is a contiguous wired and / or wireless half-duplex segment (typically using CSMA/CD), which is a subset of the subnet or vlan's broadcast domain. Collision domains are invariably a half-duplex segment, or a series of connected half-duplex segments. Ethernet hubs / Wifi Access Points (within the same RF-channel ...


15

The basic process is quite simple. I'll only cover that and omit scenarios where several DHCP servers exist, error conditions crop up or discovery has to cross network boundaries. A new client on a network sends a DHCPDISCOVER via udp from address 0.0.0.0 to 255.255.255.255:67 (broadcast, port 67). If there is at least one DHCP servers listining in the ...


15

How Routers Handle Limited and Directed Broadcasts The first thing to understand to answer your questions is that limited broadcast frames are not routed. By default when a router receives a frame with a destination address that is broadcast at either layer 2 or layer 3, the router simply drops the frame. That's why routers are said to be the boundary of ...


14

Each VLAN creates its own broadcast domain in 1 or more physical switches. If you have a switch taken out of the box it tends to put all ports in vlan 1 so for say a 24 ports the broadcast domain includes all 24 ports. If you were to create a vlan 2 and configure half the ports to be members of vlan 2 you then have 2 broadcast domains each of 12 ports. if ...


11

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 of the network and broadcast address was not so crisp as it is now. Some software treats the all-0s as a broadcast, some allows it to be a host, some neither. ...


11

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't the client just encrypt the broadcast frame using its PTK, and the AP decrypt it, ... Exactly. This is what happens. ... the AP decrypt it, then encrypt ...


9

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 any host on the network.


9

Devices in different subnets can communicate. That is the purpose of a router. Routers route packets between different networks. Even if devices in different networks are on the same layer-2 broadcast domain, you need a router to let the devices communicate at layer-3. That is because each host will compare the destination layer-3 address and its own layer-...


8

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 cross a layer-3 device, and every host in a broadcast domain must be interrupted and inspect a broadcast. Flooding is used by a switch at layer-2 to send ...


8

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 sequence of first listening for BPDU's, then learning source addresses and then finally forwarding frames. This can take ~30 seconds, during which the connected ...


7

But I do not understand how exactly routers resolves broadcast storm problem. Any explanation in detail? When a router receives a packet, it gets inspected, then forwarded out the appropriate interface or it gets dropped. When a router receives a broadcast packet, it drops it (excluding directed-broadcasts, dhcp, etc). When a switch receives a frame, it ...


7

Frame relay does not support real broadcast, it uses pseudo broadcast, meaning that it replicates incoming multicast/broadcast to all DLCIs that have the broadcast keyword on the frame-relay map statements. DLCIs learned via inverse ARP will always have broadcast enabled. When you choose the network type you tell OSPF how to behave, is DR/BDR used and is ...


7

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 resolve layer-3 to layer-2 addresses. Multicasts are are flooded to every port in the broadcast domain, albeit IGMP snooping, if supported and configured, can ...


7

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 is a broadcast address, as is 10.1.255.255/24, but without mask information, we must assume classful addressing, and 10.1.255.255/8 is a unicast address. The ...


6

You can identify Gratuitous ARPs by looking at the ARP Sender Protocol Address and ARP Target Protocol Address, so as you mentioned when they are the same it's a gratuitous ARP. See RFC 2002, Section 4.6 for a reference (the emphasis - !!!!> and <!!!! is mine)... 4.6. ARP, Proxy ARP, and Gratuitous ARP <...> A Gratuitous ARP ...


6

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 asking, "Who owns this IP address?" Broadcasts are received and processed by every host in the layer-2 domain. A multicast is received and processed by hosts ...


6

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 is ip directed-broadcast, and it must be configured on each subnet for which you want it. This is considered dangerous, and it is highly discouraged. Broadcasts ...


6

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 LAN is bounded by layer-3. The layer-2 frames are delivered to the host with the destination MAC address in the frame. I one host wants to send something to ...


6

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 performance. Apart broadcast, another problem is the number of MAC addresses a device can handle. This lead to two distinct issues: Limit of switch MAC table ...


6

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 message use the message as notification that the client has declined that server's offer. [p16] Those other servers potentially reserved an address in their ...


6

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 an area. Unknown Unicast Flooding, is a specific example of flooding, as you have accurately described in your question.


6

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 generally not routable and won't be forwarded. Directed broadcasts are routable in principle but won't be forwarded by default. However, many routers can be ...


5

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? A misconfigured mask on the client (for instance the client has a /23 mask instead of a /24) is one possible reason Does this indicate a misconfigured network client?...


5

You appear to have a VMware guest running Drobo Dashboard, and it's looking for a Drobo NAS for an iSCSI volume called iqn.1991-05.com.microsoft:desktop002.corp.virtuaprise.com. Port 5002 in this case is just a random port chosen by Drobo for this session. The global broadcast MAC address is just your switch flooding the frame to all ports because the Drobo'...


5

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 differently (based on vendor/model and configuration). However you should expect these to be dropped because broadcast is not a valid source. Switches look at both the ...


5

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? While VLAN is a tool often used to reduce the size of the broadcast domain, its major underlying goal was to partition a physical LAN device (switch, bridge) ...


5

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 effectively broadcast) traffic. The larger your L2 domain gets the more bandwidth and CPU time this eats up. Limiting MAC address counts. Most switches can handle a ...


5

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 destination address for each IP packet. Actual broadcasts, from the perspective of IP (broadcast destination address), are restricted to a single broadcast domain, and a ...


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