Questions tagged [layer3]
For questions about the OSI layer-3 (network layer).
323
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Layer 2 Encapsulation and Decapsulation in Router
Whenever the router receive a packet from the local network, router will decapsulate the frame to be able access the IP information, after router have done know which interface it will send the data ...
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Layer 3 switch SVI and static ip confusion
I have not configured the network yet. Every vlan will have a different subnet. I want to assign ip addresses to the switches on the network from another subnet. How can i provide a default gateway ...
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Layer 3 Switch IP Problem on Packet Tracer
I set up a network. It contains vlans. I assigned devices ip addresses from different subnets. I have 2 layer 3 switches to communicate them. I assigned switches ip addresses from different subnet. I ...
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2
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How can a router not recognize a gratuitous ARP MITM attack?
I'm reading the chapter for DHCP Snooping/DAI in the OCG for the CCNA and I have a question regarding how gratuitous ARP message attacks work.
I'm sure there is a piece I am missing, but I've searched ...
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How does L2 switch forward tagged VLAN?
I am a student of networking and have a question. I am currently doing an internship / project at a school where they have 3 buildings. I will name them for now
A (subnet 172.16.x.x) --> Each with ...
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Why are connected switches not a good substitute for the network layer? [duplicate]
Unless I am missing something, because switches can be chained together, I am not sure why the network layer is needed. Theoretically, one can dedicate a frame to any MAC address, and assuming there ...
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Interpretation of the name of an ITU-T document
I'm reading a document that cites a standard called ITU-T SG 13 Q5 WG. I believe that SG 13 stands for Study Group 13 and Q5 refers to Question 5. However, I don't know what WG stands for. And most ...
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Multiple hosts with same ip/subnet seperated by router possible?
Bit of a newb question but just curious if it can be done.
Is it possible to have multiple hosts with the same ip/subnet (eg 10.101.30.10/24) each seperated by a layer 3 switch/router, where one of ...
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3
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One layer 2 switch in the middle of router network
In general,
The connection should be like
PC---SW---ROUTER---Many ISP router---Router---SW---PC
so the packet will be from
layer 2 ---layer 3---layer 2
What if I put one layer 2 switch in the network
...
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Are ARP messages always used for the process of "Flooding" even when layer-3 is not involved? [duplicate]
I'm new to learning networking so please bear with me.
I've learned that ARP messages and flooding are used to find mac addresses when IP addresses are involved.
I've learned that when the mac address ...
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Is it possible to assign a default gateway per routing interface on a layer 3 switch
Here is the scenario. Currently there is a flat layer 2 network with a single /24 subnet. The intent is to segment that /24 using a layer 3 switch. On the /24 network there exists clients with ...
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548
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The use of a link local IPv6 address
In a networking course that I'm following, there was a mention of several ways of how IPv6 link local addresses can be used, such as
Assigning the link local address of a router/L3 switch as the ...
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I am trying to wrap my head around NDP
I know before PC10 can ping PC11 it will use IPv6 Neighbor Discovery to resolve the Destination MAC address for layer 2 header.
But what would the DEST MAC ADDR be and what topics can I learn this
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What does 'moving packets away from the source' in RPF means?
I recently started studying multicast and I am a bit confused by how reverse path forwarding is explained.
Most of the sources describe RPF as 'moving packets away from the source' but I understand ...
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Packet tracer is changing my addresses ipv4
Could someone help me with this?
I have a subnet with the ip: 172.16.193.0 in the fastethernet 0/0 of my router and when I go to put it in RIP the Packet tracer is changing it for another ip:172.16.0....
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Cannot get inter-VLAN routing to work
The router at the top is from the ISP and I have no control over things like WAN, NAT, etc.
Network 192.168.1.1/24 is fine, but I cannot get inter-VLAN routing between VLANs 1 and 55.
PC 1 cannot even ...
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Why hosts have routing tables?
I don't understand why hosts in a network have a routing table. Aren't all packets sent by default to the switch, and the latter determines which port to forward the packet to based on the mac address?...
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What does the network layer do at the receiver
My book (Andrew S. Tanenbaum, “Computer Networks”, Fifth Edition.) mentions while explaining the network layer that the key issue with a network layer is
determining how packets are routed from ...
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2
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Can a jumbogram (giant data packet) be used at a large scale (in WAN for example)?
There are many scientific paper for Jumbo frame, even more, some real implementations and deployments. But it is not the case for Jumbogram !!
Jumbo frame (geant frame) for Layer 2; Jumbogram (geant ...
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Can a switch fragment a jumbo frame?
In all resources seen that tackle the term of "jumbo frame", I understand that it is applied in a LAN, because:
It's a Jumbo frame, and a frame is for Layer 2
These resources talk a lot ...
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Does the IP header have a "Padding" field?
I found two images of the IP header, one image shows a field called "Padding", while the other image don't show the "Padding" field:
Which one of these two images is correct?
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Where is priority for a particular frame set?
The Medium Access Control sublayer appends 3 bits for the priority of the frame. The possible choices for the priority are
Traffic Type
Priority
Background
0 (lowest)
Best effort
1 (default)
...
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Configuring HSRP on multiple L3 devices
I am currently doing an enterprise campus network which consist of Three Tier hierarchy and a simple MPLS design.
Currently, I'm stucked at HSRP configuration on the Core Layer to the Edge Router. ...
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Routing VLANs to Firewall Ports
My network has 3 VLANs: 10, 11, 12, and their address spaces are 10.0.X.0/24 where X is the VLAN ID. Their default gateway is a virtualized pfSense (even though it's virtual, I will use terminology as ...
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2
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Is DHCP in the application layer or the network layer?
Tanenbaum's Computer Networks says:
5.6 THE NETWORK LAYER IN THE INTERNET
...
5.6.4 Internet Control Protocols
In addition to IP, which is used for data transfer, the Internet has
several companion ...
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6
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How Does A Layer 2 Switch Differentiate Between Different Networks?
I know that different IP-based networks can be connected to the same layer-2 switch. and I know each network's nodes can communicate just fine, however, no normal traffic can occur between two nodes ...
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ICMP codes in response to ICMP traffic, not UDP/TCP
I am trying to wrap my head around a concept and I am having some trouble. If I ping 8.8.8.8, 10.8.1.1 replies to me "Destination port unreachable".
Ping uses ICMP, so it does not have a '...
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157
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Ospf multicasting with two different group
Suppose I have one ospf network where two multicast group exists. And some routers is ospf which belongs to one group or multiple group (Like: routers E, H) and router is layer3 router (Like: ...
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393
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Custom option in IP header
I would like to add (or piggyback on an existing not used) a custom option to the IP header. I've full control of the IP stack at both end points, but I've no control on all the hops in the route (...
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Fragments taking different routes?
I have trouble understanding why sometimes it occurs that during IP fragmentation certain fragments take different routes. I was following this the second example:
https://www.gatevidyalay.com/ip-...
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How n level come to know the n+1 level contents?
Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
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Actually ICMP message makes layer3 reliable?
We know that ICMP is connectionless because it does not require hosts to handshake before establishing a connection.
But when packets gets dropped in between route then respective router informs the ...
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Router could get packet of size more than 1500 bytes?
Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes.
My question is so fragmentation is happening at ...
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Time taken to complete a routing table update and possible interruption
I am wondering if a routing/forwarding table update at a switching node (e.x., a switch or layer-3 router) can cause momentary packet drop or increased delay for a data stream that will traverse this ...
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Understand router Ip address and Mac address, Switch Mac address
Scenario:1
Suppose external Router R1 has interface a connected with interface b of the site Router R2. And Router R1 using IP address 80.0.0.0/8 for a. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0....
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Which ranges of IPv6 and IPv4 do requests to the local network and the host?
I'm looking for the range of IP address that is bound to the local network or the host itself.
So far for IPv4 I found:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255....
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Does a Transparent Firewall need a Default gateway if directly connected to a layer 3 device that is actively performing routing?
Good folks of the Network Engineering stack!
I have a question that I assume most people could answer in their sleep. To better illustrate my question, I've provided a sketch of my network below.
In ...
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546
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Acknowledgement, retransmission of layer2 is actually belongs to layer4?
I followed from this question understand that only transport layer responsible for acknowledgement. But I have read on book stop and wait, GBN, SR protocols uses acknowledgement, retransmission in ...
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What is responsibility of different layers of OSI model and intermediate devices between sender and receiver when data packets are lost/corrupted?
Suppose sender sending some data to receiver and there are 3 routers between them. R1, R2, R3 are routers.
Now sender starts sending data packet D through it's AL, TL, N/W L, DLL,PL to router R1 ...
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Does a gateway always have to be on the same subnet as the host IP address? [closed]
The obvious answer is yes, I suppose, but my VPS provider doesn't seem to agree.
I've just uploaded a Ubuntu 20.04 instance, and the provider is telling me:
IP address: 77.xxx.yyy.zzz/32
Gateway: 10....
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Best way to configure layer 2 daisy chain with 2 layer 3 switches/gateways at either end?
I would like to implement a linear daisy chain for the purpose of transmitting internet over a considerable distance.
One motivation behind the use of a linear daisy chain for this problem is that ...
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Could we use private IP address as directed broadcast address?
We know that private IP addresses ranges of class A, class B, class C are 10.0.0.0-10.0.0.255, 172.16.0.0-172.16.255.255, 192.168.0.0-192.168.255.255 respectively.
My first questions is that first and ...
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Layer 3 switch as access switch
Is it possible to have Layer 3 switches at access level (meaning the PCs are connected to it) if multiple VLANs are spread out accross multiple switches? For example, VLAN 10 is present at SW1 and SW2....
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Logs on my Cisco ASA show the public gateway (ISP router) is pinging the internal network, how? [closed]
Im (remotely) working with an issue where the network has intermittent drops. i suspect possible routing loop, but havent confirmed that yet.
In the logs of our Cisco ASA 5506, i see that the public ...
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752
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Does a router work both on Layer 2 and Layer 3? [duplicate]
According to TCP/IP model router works at Layer 3. But when data has to be transmitted to different network it is based on IP address but hop-to-hop transmission is based on MAC address.
That means ...
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What is the minimum MTU of IPv4 68 bytes or 576 bytes?
I read that 68 bytes is the minimum size of IPv4 datagram every device must be able to forward without further fragmentation.
576 bytes is the minimum size of IPv4 datagram every device has to be able ...
user80210
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Why two routers connected via PPP don't use ARP but Ethernet requires ARP?
I have read from @Ron Maupin's answer of this question that your two routers are connected via PPP (this is not uncommon), ARP will not be used , but if the two routers are connected via ethernet, ...
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3
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Why does OSPF use flooding despite using multicast?
We know that flooding is only possible in layer2 switch. But in OSPF router in layer3 uses flooding with multicasting. Suppose we have one router in OSPF uses multicast address 225.0.0.9. If router ...
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How in Distance vector routing one router communicates adjacent router through broadcast address and OSPF uses unicast with another?
In distance vector routing algorithm one router can communicates(shared the routing table) with adjacent router by broadcasting message which are in same subnet. OSPF uses flooding to unicast message ...
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Are IPv4 type of service and IPv6 traffic class equivalent to each other or is traffic class IPv6 specific? [duplicate]
IPv6 has a traffic class field. According to the specification it is an IPv6 length, out of which first 6 bits are called code point or differential services code point (DSCP) and the last 2 bits are ...
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