Questions tagged [layer3]

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

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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) ...
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47 votes
3 answers
130k views

What is the difference between MSS and MTU?

I'm confused as to the difference between maximum segment size and a maximum transmission unit. Can someone please explain in relation to layers 2 and 3? If I had a packet of 800 bytes in the ...
NetworkNinja's user avatar
11 votes
3 answers
2k views

What is a "Layer 3 Switch"?

What is a "Layer 3 Switch"? I essentially understand the OSI model, well maybe I don't and maybe that is why I don't understand. Its just that I don't see how/when/if a "managed switch" becomes a "...
Mark Christopher's user avatar
9 votes
5 answers
3k views

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page?

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page (same layer as IP) when the ICMP protocol data is a payload of the IP packet? This is the article on Wikipedia that states ...
yoyo_fun's user avatar
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8 votes
3 answers
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Does a switch understand packets? If yes, what is the frame terminology for?

I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
Taha's user avatar
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3 answers
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Does a router send frames or packets?

Perhaps it's a novice question, but does a router send/receive frames? When I read about this subject, it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in ...
Smbbo's user avatar
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5 votes
5 answers
550 views

What blocks a computer from another network in the same switch from answering an ARP request?

Let's suppose I have 3 computers A, B and C connected to the same switch with only the native VLAN active. A and B belong to the same network, let's say that their IP addresses are 192.168.1.1/24 for ...
caiokameda's user avatar
3 votes
3 answers
7k views

At which layer does router operate?

I have studied from various sources that router is a layer 3 device. It does routing based on Network layer (layer 3) header, but I have a doubt. Network address translation (NAT) is a feature of ...
Raja's user avatar
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2 votes
6 answers
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Is a "LAN" a layer 2 or a layer 3 concept, in TCP/IP?

I think my question is purely theoretical and a matter of definitions; it derives from the fact that a L2-switch with VLAN capabilities is able to "create" different virtual LANs, and thus I am led to ...
Maurizio Carcassona's user avatar
2 votes
2 answers
559 views

CGN and its advantages

I have been reading about CGN. Though similar to NAT it is used by service providers to route traffic without the need for the a public IP address. But when the packet leaves the ISP to the public ...
john 's user avatar
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22 votes
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What do TCP/UDP add to "raw ip"?

I know that both TCP and UDP are built on top of IP, and I know the differences between TCP & UDP, but I'm confused about what exactly "raw ip" is. Would it be fair to say that TCP & UDP both ...
John Dorian's user avatar
22 votes
6 answers
72k views

What, exactly, is required to make Airplay work across VLANs? [closed]

It seems like AirPlay works out-of-the-box, vaguely speaking, only within a LAN. It's not clear to me exactly why, but it looks like at least discovery relies on broadcasts. Wikipedia states that ...
alx9r's user avatar
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13 votes
4 answers
37k views

What layer of the OSI model does NAT work?

Simple question and the answer is layer 3 of course, but can we say that PAT is working on layer 4 also because it deals with port numbers which is a layer 4 function? Or is it only a layer 3 ...
aia87's user avatar
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13 votes
1 answer
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Can a router send ARP requests to hosts?

I play with libpcap in C recently to create an arp sniffer program that captures arp requests on the air. I came up with a strange effect. I captured arp requests from my router. I don't know if this ...
user avatar
13 votes
1 answer
34k views

RIB vs FIB differences?

Can someone explain the differences between a RIB and FIB a little further? I didn't see any similar questions on the site so I thought this would be a good addition. The RIB routes and the FIB ...
stets's user avatar
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9 votes
4 answers
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Advantage of layer 3 switch over Router

What is the advantage of Layer 3 switch over the Router ??
Abiral's user avatar
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8 votes
5 answers
755 views

Why is the IP layer aware of higher layers in the network stack?

In the IP packet header there is an 8-bit Protocol field (at offset 9) that holds the "next level protocol", with assigned numbers given in RFC 790. For example, TCP is 6. My question is, why is the ...
I. J. Kennedy's user avatar
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 ...
Shadi's user avatar
  • 285
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 ...
voices's user avatar
  • 313
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 ...
stefanbschneider's user avatar
5 votes
1 answer
371 views

Optimizing Network Topology

Recently I wish to split the network by VLANs. Mainly for two reasons Exclude management interfaces from the commonly accessible lan Separate WiFi traffic (security and broadcasts) The current idea ...
Dex's user avatar
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4 votes
3 answers
2k views

How does a router a layer 3 device translate port address in PAT, as it is a layer 3 device?

While I was reading about PAT i.e Port Address Translation.The router was configured to translate all the private IP addresses to one single public IP.Since router is a layer-3 device, it can do that ...
PRANAY KASTHALA's user avatar
4 votes
2 answers
947 views

Can I Use BGP as an IGP - Multisite w Redundant Layer 3 MPLS WANs

The requirements are Hundreds of sites. Each has a router and firewall and a switch stack. Layer 3 MPLS WAN with BGP to provider VRF. BGP as an IGP? iBGP Would you distribute a public ASN across all ...
Ronnie Royston's user avatar
4 votes
3 answers
1k views

What practices/ mechanisms/ protocols can be used to secure communication on physically exposed Ethernet links?

Given that Ethernet cables are everywhere and use for all kinds of links and it is assumed they are physically guarded, hence typical installations do not leverage any "secure" mechanisms. Let's say ...
Alex S's user avatar
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3 votes
4 answers
2k views

Should I receive an ARP reply from a host that is logically on a different subnet but is connected to my host via a hub?

Host A: 128.238.66.100/16 Host B: 128.238.67.100/24 The hosts are connected to the same hub and nothing else is connected to that hub. The routing and ARP tables of both hosts are empty. Host A ...
George's user avatar
  • 538
3 votes
3 answers
8k views

D-Link L2 & L3 Network Setup

I'm currently setting up my new network using D-Link DGS-1510 series gigabit stackable smart managed switches. It is the first time i use this L2 & L3 switches and I'm trying to setup the ...
user6829's user avatar
2 votes
2 answers
1k views

Exiting to a Router from Layer 3 Switch with SVI enabled routing

I am trying to simulate a network, I am having problem directing traffic to exit the L3 Switch and to go to router for routing to outside network. (I don't want to use routing capability of switch, ...
cRAYonhere's user avatar
2 votes
2 answers
703 views

IP Fragmentation

When Device A sends an IP datagram toward Device B, the IP Layer of Device A computes if it must or not fragment the IP datagram to fit the link MTU. Sent to the next hop, the process will be repeated....
Shinomoto Asakura's user avatar
1 vote
3 answers
3k views

Minimum MTU size on Ethernet and minimum Ethernet frame size

I am a bit confused about the understanding of the relationship between minimum MTU of MTU and minimum Ethernet frame size. We know that the maximum MTU of Ethernet is 1500 Bytes which makes the ...
ERH7777777's user avatar
1 vote
2 answers
533 views

Two Layer 3 Switches to one router

So I have a cisco 2811 router and 2 3560 switches Currently the router is connected to Core1 only, what i would like to do is use the other port on the router (fa0/1) to connect to Core 2. How do I ...
NickCarlt's user avatar
1 vote
1 answer
287 views

How UDP checksum get IP address to make pseudo header in transport layer?

We know that UDP checksum's pseudo header contains the most important parts of the IP header, that is, source and destination address, protocol number and data length. I hope that the concept of IP ...
S. M.'s user avatar
  • 378
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
1 vote
1 answer
19k views

How can I apply an ACL to interface on a Layer 3 switch?

I try to accept ACL on L3 switch inteface. I've created standard ACL via: SW-L3(config)#access-list 1 permit host 1.1.1.2 SW-L3(config)#access-list 1 permit host 1.1.1.3 Then i tried to execute this,...
Daniil Rutskiy's user avatar
0 votes
1 answer
628 views

Why is default gateway in routers configuration usually set as an IP address?

I mean why not just: a MAC address? It should eliminate the need in ARP requests asking for gateway address. Also it should eliminate the need in changing IP addresses in settings when gateway IP is ...
KOLANICH's user avatar
  • 111
0 votes
2 answers
642 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
  • 378
0 votes
3 answers
165 views

Regarding Cisco's hierarchical network design

why routed ports usually implemented between the distribution layer and the core layer ? why not just extend the layer 2 domain to the core layer ? is the other design model more practical than this ...
Zero Frame's user avatar