Questions tagged [layer3]

For questions about the OSI layer-3 (network layer).

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TCP/IP and data cut

I would like to clarify my understand about TCP/IP model and packet cutting. I think it's done by layer 3 (Transport, eg. TCP) but I'm note sure about layer 2 (Network, eg. IP) or even layer 1 (...
PanCho's user avatar
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Identification field in ipv4 [duplicate]

What is the actual use of identification field in ipv4 and also does the same fragment packet Will share the same identification value
Darevil294's user avatar
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1 answer
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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 ...
Darevil294's user avatar
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1 answer
114 views

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 ...
shiva13's user avatar
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1 answer
82 views

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 ...
shiva13's user avatar
2 votes
2 answers
112 views

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 ...
Alex's user avatar
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2 answers
196 views

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 ...
Bartballon's user avatar
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26 views

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 ...
Aviv Aviv's user avatar
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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 ...
JosefMaier93's user avatar
1 vote
2 answers
588 views

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 ...
Hudson Marine's user avatar
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3 answers
156 views

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 ...
jacky chong's user avatar
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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 ...
William's user avatar
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2 answers
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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 ...
Digital ink's user avatar
1 vote
1 answer
707 views

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 ...
Mitrixsen's user avatar
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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
s3lectstar's user avatar
5 votes
2 answers
423 views

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 ...
Marcus's user avatar
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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....
JBALTAN's user avatar
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280 views

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 ...
ruyelpequenocid's user avatar
1 vote
1 answer
436 views

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?...
Mehdi Charife's user avatar
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2 answers
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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 ...
Essam's user avatar
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2 answers
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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 ...
Lee's user avatar
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1 answer
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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 ...
Lee's user avatar
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5 votes
2 answers
516 views

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?
user4582812's user avatar
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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) ...
user84425's user avatar
2 votes
1 answer
183 views

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. ...
ccnanewb99's user avatar
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1 answer
136 views

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 ...
Jeremy's user avatar
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3 votes
2 answers
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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 ...
Tim's user avatar
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8 votes
6 answers
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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 ...
Shadi's user avatar
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1 vote
1 answer
378 views

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 '...
user83344's user avatar
1 vote
1 answer
169 views

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: ...
S. M.'s user avatar
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2 votes
1 answer
477 views

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 (...
Uri London's user avatar
2 votes
1 answer
170 views

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-...
mato_kan's user avatar
1 vote
1 answer
114 views

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 ...
S. M.'s user avatar
  • 378
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1 answer
38 views

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 ...
S. M.'s user avatar
  • 378
1 vote
1 answer
249 views

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 ...
S. M.'s user avatar
  • 378
3 votes
2 answers
659 views

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 ...
Danny's user avatar
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0 votes
1 answer
136 views

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....
S. M.'s user avatar
  • 378
2 votes
1 answer
98 views

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....
Jimmy's user avatar
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1 vote
1 answer
79 views

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 ...
Jason's user avatar
  • 13
0 votes
2 answers
613 views

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 ...
S. M.'s user avatar
  • 378
0 votes
2 answers
651 views

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 ...
S. M.'s user avatar
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1 vote
2 answers
2k views

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....
EML's user avatar
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1 vote
2 answers
468 views

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 ...
Doug's user avatar
  • 13
0 votes
2 answers
266 views

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 ...
S. M.'s user avatar
  • 378
1 vote
1 answer
264 views

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....
Quirik's user avatar
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1 vote
0 answers
101 views

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 ...
TechEng's user avatar
  • 21
1 vote
1 answer
859 views

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 ...
Rohit's user avatar
  • 31
1 vote
2 answers
3k views

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 ...
user avatar
4 votes
2 answers
911 views

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, ...
S. M.'s user avatar
  • 378
2 votes
3 answers
648 views

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 ...
S. M.'s user avatar
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