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 (...
0 votes
0 answers
16 views

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
0 votes
2 answers
3k views

intervlan routing with PfSense

I Need some guidance on getting my lab networking configured. Any support is appreciated. My Lab consists of: 2 cisco switches: 2960s(access layer 2) and 3750X(ip routing/layer 3) Xenserver with ...
0 votes
1 answer
37 views

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 ...
2 votes
2 answers
977 views

Question about MTUs vs maximum frame sizes - what is their difference?

I am currently studying networking at university and I have a question about MTUs and maximum frame sizes. What is the difference between the MTU and the maximum frame size? This Wikipedia article ...
12 votes
4 answers
143k views

What are the reasons for seeing an incomplete ARP?

As was mentioned in this post: The reason for seeing an incomplete ARP is that "An ARP request was sent for that address, but the host with that address is not up and running on the LAN, so there is ...
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 ...
0 votes
1 answer
113 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 ...
0 votes
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 ...
4 votes
2 answers
906 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, ...
0 votes
2 answers
431 views

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 ...
0 votes
2 answers
186 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 ...
0 votes
0 answers
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 ...
0 votes
0 answers
18 views

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 ...
1 vote
2 answers
571 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 ...
1 vote
1 answer
375 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 '...
0 votes
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 ...
0 votes
0 answers
16 views

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 ...
1 vote
1 answer
695 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 ...
5 votes
2 answers
506 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?
0 votes
1 answer
85 views

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
0 votes
1 answer
197 views

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....
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 ...
2 votes
1 answer
97 views

The length of Fragment header in IPv6

From RFC2460 :https://www.rfc-editor.org/rfc/rfc2460#section-4.5, the length of the fragment header seems to be fixed 8 bytes. But when I test with Scapy with the default fragment header, from sniffer ...
6 votes
6 answers
34k views

Difference between routing, forwarding, and switching

I feel like the three terms are often used as synonyms but actually all mean something different. I did look at Wikipedia sites but I'm still unsure about the definitions of the three. From my ...
0 votes
2 answers
274 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 ...
1 vote
1 answer
425 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?...
0 votes
2 answers
119 views

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 ...
3 votes
2 answers
2k views

Why do transport layer do data chunking. If there is fragmentation in Network Layer

I just curiously wanted to know about the question regarding L4, L3 Data Chunks, IP Fragmentation : Data chunking happened at Layer 4(Transport, TCP), and Fragmentation at Layer 3(Network, ipv4) ...
7 votes
4 answers
14k views

Is it possible to perform a Layer 2 (MAC address) traceroute?

I understand the difference between layer2 & layer3 and MAC & IP. I understand address resolution protocol, etc. But is there any way to do a traceroute that will show Layer 2 information? For ...
5 votes
2 answers
710 views

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 ...
1 vote
1 answer
663 views

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 ...
2 votes
1 answer
169 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-...
0 votes
2 answers
123 views

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) ...
2 votes
1 answer
176 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. ...
2 votes
2 answers
194 views

How does Network Layer behave when client received a unicast DHCP offer?

I went through various stack exchange post to understand the concept of DHCP offer when it comes as a unicast to client from the DHCP server. A server can send a unicast DHCP offer since it knows the ...
0 votes
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 ...
3 votes
2 answers
3k views

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 ...
2 votes
3 answers
6k views

What is the relationship between the IP address and MAC address?

I own a MAC address and I want to know from it, the IP address.
8 votes
6 answers
5k views

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 ...
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: ...
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....
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....
3 votes
2 answers
651 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 ...
2 votes
1 answer
472 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 (...
1 vote
1 answer
271 views

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 ...
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 ...
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 ...
0 votes
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 ...
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 ...

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