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Questions tagged [layer2]

For questions about the OSI layer-2 (data-link layer).

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1answer
23 views

Logical Link Control (LLC) vs Medium Access Control (MAC)

What differs the LLC sublayer from the MAC sublayer? From what I've understood - The MAC sublayer does what the PHY layer should be doing: detection (error, collision), channel listening, analog-to-...
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0answers
31 views

What services does the physical layer provide to the link layer? [on hold]

The physical layer is responsible for transmitting raw bits, bit-by-bit, over a physical medium. It is concerned modulation, multiplexing, transmission type (duplex), etc. But what is the minimal set ...
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1answer
31 views

Unicast Adjacency Routes Nexus (AM) Cisco Nexus

I have an odd situation. There is static route on my Nexus 7700 that routes anything for specific subnet /24 to a F5 LTM Load Balancer, external VRRP interface 10.x.153.15. As you can see below, ...
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2answers
55 views

Clock Synchronization in a Network

I had a query in Clock Synchronization in a LAN.. If we already have clock synchronization in a network with the help of preamble field in an Ethernet frame. Why should we need still protocols such ...
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1answer
47 views

Is there any fixed version of CSMA/CA?

I was trying to understand exact algorithm for Carrier Sense Multiple Access / Collision Avoidance mechanism from Forouzan's book. The book gives very detail explanation of topics. However explanation ...
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1answer
52 views

What is the theoretical difference between the link layer and the network layer?

I have run into this problem again and again and have never found a sufficient answer to this question. I want to understand the fundamental, theoretical difference between a layer 2 network and a ...
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1answer
31 views

N2K-C2248TP-1GE question

We are working with Cisco 2960 and Cisco 4948 switches as our top of rack switches and we want to purchase some N2K-C2248TP-1GE , and connect N2K-C2248TP-1GE to our edge switches, (our edge switches ...
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3answers
68 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 ...
2
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2answers
275 views

Router on a stick not connecting 2 different VLANs

I have a setup which requires two different VLANs to be able to ping one another. I have a setup with 2 - layer 2 switches and a router that has defined sub-interfaces, and for the life of me, I ...
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1answer
22 views

Broadcast Timer [duplicate]

This question is regarding in the process of L2 MAC Address learning. As we know, if a sender sends a packet to some receiver host which switch doesn't know, it will broadcast for learning. Assume an ...
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1answer
76 views

Ping across VLANs using layer 2 switch

I'm trying to ping one PC on one particular VLAN (VLAN 80) from another PC on a different VLAN (VLAN 50). I have a layer 2 switch (Cisco 2950T), so I can't do it from within itself. How would I be ...
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2answers
109 views

Different MAC addresses [closed]

What happens if a host on the network receives an IP packet with a MAC source address that differs from the MAC address in the local ARP table for that source IP. The ARP table entry for that IP was ...
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1answer
45 views

What's the LAG interface period be if the two switches have different periods set

Considering a LAG interface between two devices A and B, A is configured to have LACP fast transmission and B to be LACP slow what would be the resulting aggregate interface's period be?
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2answers
106 views

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 ...
4
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3answers
145 views

JunOS, access mode interface asks for a vlan

I'm kinda new to networking so I'm going to do my best to try explain my issue. The issue that I have is that I want to delete all default configuration for my xe interface. Current configuration: ...
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1answer
76 views

Layer 2 and Layer 3 traffic with one cable

Hers the topology. L2 switch L3 switch Router There are 2 VLANs. One VLAN ends on the L3 switch 1 VLAN on the router. Here is the question. Can i connect the L3 switch and the router with just 1 ...
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1answer
47 views

Bit stuffing and Error correction combined

If I understand correctly both error detection/correction and framing are done at the link layer. I understand how popular error detection/correction and framing techniques work. But I struggle with ...
2
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2answers
233 views

What are neighboring ports?

I know this is as basic as it gets but I can't find a direct answer to this question. Are they ports on two different switches (or routers) that are connected by a cable? Are they the ports ...
1
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1answer
218 views

Flooding vs Unknown Unicast Flooding

Can someone clarify what is the difference between Flooding and Unknown Unicast Flooding? Is it the same thing or it contains different meaning? I'm aware that Flooding happens when a switch ...
3
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1answer
660 views

Difference between Giant Frame and Jumbo Frame

Can someone enlighten me the difference between Giant Frame and Jumbo Frame? From what I hear, Giant frame is a frame with the size greater than 1518 Bytes excluding Preamble, Frame Delimiter and ...
3
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3answers
510 views

Collision domain question

I'm studying for my CCENT exam, and not quite sure why the book (official Cisco) says that there are 5 collision domains in this example. Isn't it supposed to be 4? The hub on the left, the hub in the ...
5
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2answers
818 views

What precisely is a link?

When reading about layer 2 the word "link" is frequently used but strangely I'm struggling to find a formal definition of it. What is the precise definition of a link? So in the image below, how many ...
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0answers
18 views

DHCP Layer 2 and Layer 3 [duplicate]

I am having a difficult time to visualize the conceptions of DHCP Discover message in order to receive an IP address sends out a broadcast at both layer 2 and layer 3. Can someone care to explain? ...
0
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1answer
72 views

Wireshark remote hosts

I configured a rip network. I connected two PCS to router 1, router 1 is connected to router 2 and PC 3 is connected to router 2. When I pinged PC 3 and looked at this in wireshark, in the source it ...
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1answer
84 views

sequence number layer 4 vs sequence number LLC layer 2

I had read about TCP in layer 4 where sequence number and acknowledgment numbers were assigned to each segment so that each side of the connection could keep track of the process of sending/receiving ...
2
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2answers
121 views

Please help me understand this simple arp request / reply - how does a router know an IP address without knowing the MAC address?

I am new to networking, I am using Wireshark on my home PC to learn about ARP. I understand that ARP is used to build the ARP cache, which correlates IP addresses to MAC addresses on a LAN. ARP ...
3
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2answers
77 views

How does ethernet understand what is the upper layer? What are the values in Ethernet II field?

How does ethernet understand what is the upper layer of a frame? What are the values in Ethernet II field? Ethernet is in data link layer, so the upper layer is network layer. When processing at ...
3
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1answer
457 views

MAC Table vs ARP

I understand that for a switch to learn a MAC address, if host A wanted to send data to Host B the switch learns host A MAC and places it in the MAC table. If it doesn't know where the MAC (for Host B)...
1
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1answer
52 views

Dhcp Broadcast Through Switches

Think of a pc connected to switch1. Sw1 is connected to sw2(trunk port on both switches) and sw2 is connected to a router(dhcp server). Pc sends a dhcp broadcast. Does sw1 passes the broadcast through ...
0
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1answer
145 views

Does the PHY signal interframe gap to the MAC?

I'm trying to decode an Ethernet II frame with type instead of length indication. Theoretically this should be done by receiving and storing the data between start of frame and interframe gap. However ...
1
vote
1answer
63 views

DHCP Broadcast on SVI

Think of a dhcp broadcast going through multiple switches. What happens to that broadcast when it reaches the vlan interface (svi)?
3
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3answers
569 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 ...
2
votes
3answers
713 views

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 ...
2
votes
1answer
73 views

Is it worth the effort to split up in layer 3 with point to point links? [closed]

I have this technical question. With my family we have a little business. I got to provide internet access to three places, separated a few hundred meters each other. I need to allow to watch the ...
4
votes
2answers
602 views

Nexus 3172T MTU

I am attempting to set the L3 mtu on a Nexus port. The mtu option is only available if I set "no switchport" which then prevents me configuring VLAN related settings. Am I missing something obvious? ...
1
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2answers
33 views

How can subnets not fulfil symmetric property?

While studying Internet Protocol, I came upon the following example of two devices: Device A: IP address: 10.1.1.1 Subnet mask: 255.255.255.0 and Device B: IP address 10.1.1.200 Subnet mask 255....
6
votes
2answers
409 views

How to connect a special device in a network

I have a question which is puzzling me. I have a couple of custom electronic devices (are identical, one is a master and the other is a slave) which implement only up to level 2 of the ISO/OSI layer, ...
5
votes
1answer
378 views

How does STP convergence work?

Consider the IEEE 802.1D (first revision) Spanning Tree Protocol. I have read a lot of articles and forum entries about STP convergence. Often I do find contradictions about the convergence mechanics. ...
1
vote
1answer
510 views

Firewall on a stick for Intranet and static routing

I have a question about possible problems that can occur with this network design. If I have an intranet with a firewall on a stick design, multiple switches with layer 2+, is this setup fine? or ...
1
vote
1answer
228 views

Help with small office setup - Cisco SG350 28 port switch

I have very limited knowledge in Cisco IOS but in a crucial state to setup up a small office network. I have bought 2 Cisco SG350 28 port Layer 3 switch, Switches should be enabled with VLAN and VTP. ...
3
votes
2answers
792 views

L2 / L3 on CISCO ASR

I am new to CISCO and have the following problem: I have 3 routers. Between these only one physical connection. The VLAN 100 is connected to R1 and R2. The VLAN 200 is connected to R1, R2 and R3. The ...
1
vote
1answer
158 views

Why do I see “ethernet” keyword in my wlan0? [closed]

When I check my wireless network card interface with the command ifconfig wlan0: ether -my-mac-adress- (Ethernet) I just started to learn this stuff, but I thought Wifi and Ethernet are kind of ...
4
votes
4answers
1k views

Do layer 3 protocols use layer 2 protocols?

I saw the STP on layer 2. The guy that made the tutorial says at the end : Even though it seems that Layer 2 access layer solutions are slowly being replaced by blazing fast Layer 3 solutions. ...
4
votes
2answers
515 views

Spanning Tree on the interface that resides at end users

I do not understand why we use portfast and in fact STP on the interface of a switch that is directly connected to end users. Indeed, a user can interfere with the STP election and perform DDoS (that ...
5
votes
2answers
73 views

How the packet is routed between two host from same sub-net and associated with same AP?

Given host 'A' and 'B' have IP 10.10.0.5 and 10.10.0.8 respectively, the sub-net mask for both are 255.255.255.0, both 'A' and 'B' are associated and connected to the same AP, and the AP is connected ...
1
vote
1answer
63 views

Counting the Number of re-transmission for a single UDP packet transmission in IEEE 802.11?

I was working with a client-server project based on UDP and 802.11 as a link and physical layer. There, the client was trying to probe some packets in the wireless channel to gauge channel condition. ...
7
votes
2answers
427 views

How is the Groupwise Transient Key used in WiFi networks?

In Wifi WPA, I understand that during association, a 802.11 client and AP negotiate a Pairwise Transient Key (PTK), using which the Groupwise Transient Key(GTK) is provided to the station. I ...
3
votes
2answers
502 views

Does WiFi broadcast traffic from a station go through the access point?

Let's say I've got two devices connected to my Access Point, a laptop and a tablet. If the laptop sends unicast traffic to the tablet, I understand that it must go through the AP. However, how is ...
1
vote
1answer
44 views

How to understand the rectangle shape wave? [closed]

I am read a tutorial: there is example, says the source signal waveform like this. I can not understand this, because I did not laid eyes on the rectangle shape wave. who can explain to me?
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0answers
17 views

Is the analog signal or digital signal inside the twisted pair? [duplicate]

Is the analog signal or digital signal inside the twisted pair? In our network, the twisted pair linked to Switch and Hosts. I want to know the twisted pair's signal is analog signal or digital ...