Questions tagged [layer2]

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

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26 views

In RSTP, where all switches generate their own BPDUs, are they limited to forwarding them only on designated ports? (like in classic STP)

I recently learnt a rule in STP: only Designated ports forward BPDUs. However, I'm not sure about this in RSTP since ALL switches generate their own BPDUs every few seconds. So, in a certain LAN ...
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1answer
25 views

Where can I find virtual switches to learn about layer 2 [closed]

I am learning about layer 2 networking, arp, cam tables, mac addresses etc. I will like to see some of these things in action but I do not have access to physical hardware now, does anyone know of a ...
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2answers
40 views

How does an L3 Supported Switch differentiate L2/L3 Packets?

I had a managed or layer 3 supported switch (it can process both layer 2 and layer 3 packets). Now a packet from a connected host comes to it, sending traffic. How does the switch decide to process it ...
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15 views

Switch vs. Router and sequence of OSI Model [duplicate]

As I understand it: A switch (layer 2) seems to define a LAN and a router (layer 3) enables communication between distant LANs. A device on a LAN will give it's MAC address to the switch upon ...
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2answers
53 views

Some extra clarification regarding VLANs and SVI

Good afternoon guys, I've got a question regarding VLANs and SVIs. First of all, I know some concepts about VLANs, and I've been in the IT field for a while. But this one is a bit confusing for me. ...
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11 views

Query regarding ethernet header [duplicate]

I have a query regarding ethernet header. Some representation of ethernet header have Type Field and some tell it as Length field. Which is the right one here ?
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1answer
19 views

Why does SONET need atomic clock but T-carrier does not?

SONET and T-carrier are both synchronous TDM. But T-carrier does not use atomic clock. Why does SONET? Is it because SONET does not use buffer? But how does it prevent bit loss if there is no ...
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2answers
50 views

MAC address and unicast, multicast and broadcast

I'm very new to computer networking and I'm trying to figure out this dilemma about the Unicast, Multicast and Broadcast transmissions. I was told that MAC address are unique for each device and they ...
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2answers
43 views

What if my data contains nothing but Preambles and Start of Frame numbers?

Will that continually reset the receiving NIC or is there a sort of escape character that need to be used if my data contains nothing but alternating 1s and 0s in 7 byte blocks with start of frame ...
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1answer
23 views

Is SONET a physical layer or a data link layer?

According to some sources, SONET is physical layer. But some sources say that SONET can carry IP directly. Also, SONET defines its own frame -- it has a header and a payload. That must make SONET a ...
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2answers
33 views

Query regarding LACP System Priority

This is regarding LACP System Priority. From my research I could find the following info pertaining to system priority. LACP combines the System Priority value with the MAC address of the switch to ...
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1answer
24 views

Query regarding LACP timeout flag

Say we have two swicthes. Switch A and Switch B. Switch A sends LACPDU's with timeput flag set to 1 (fast). Switch B sends LACPDU's with timeout flag set to 0 (slow). By researching came to know that ...
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3answers
75 views

Why is in all arp table snmp oids an interface index before the ip number?

When I want to get arp information about a single ip number or subnet, I have to snmpwalk the whole arp table, as some oid architects had the "great" idea to always insert an interface index ...
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1answer
25 views

BPDU Header System ID Extension

Previously network switches was using the 8 byte field Bridge Priority to identify a root on the network.When networks grows and becomes complex vlan creation comes into play the 2 bytes Bridge ...
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3answers
51 views

Propagating Static MAC Addresses

I have a situation where I need to place a static MAC on a switch as the server in question does not generate any outbound traffic. This static MAC seems as if it will work for hosts on the same ...
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1answer
36 views

How loops appeared when skipped listening and learning state?

In STP convergence process, I just know that after a link failed a blocking port become listening state for 15 seconds then learning state for 15 seconds. I've read a CCNA 200-301 Guide explained me ...
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1answer
29 views

Private VLANs Same As VLANs!

The common VLANs provides a layer 2 speration flooding and broadcasting is limited to each virtual lans. Im wondering what is the purpose of the private VLANs also the secondary VLANs (isolated and ...
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1answer
35 views

When traffic is intiàted from pc is ANDing process or ARP process start working first

When traffic is initiated from desktop which process starts first; the ARP process or ANDing process?
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1answer
34 views

How a wifi AP handle packets

Computers are connected to a wifi AP. The wifi AP is connected to a L2 switch. A server is also conected to this switch. When computers sends packets to the server, how the wifi AP manages the paquets?...
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2answers
66 views

Connecting switches together

I have L2 switches which will be daisy chained together (yes I know, daisy chaining isn't great, but anyway..) The L2 switches will then link to a L3 switch. Both the L2 and L3 switches have x4 10GbE ...
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3answers
128 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 ...
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2answers
125 views

Confusion about MTU

I am studying about IP fragmentation and MTU. What I know is MTU is the property of Physical medium, as in the amount of data it can process without having to fragment the data. The default MTU on ...
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2answers
46 views

Is the outgoing interface of a router in the same Subnet as the Incoming interface of the NEXT HOP router?

In the TCP/IP Volume 1, it is stated that ARP works only on the same subnet. Does this mean that the outgoing interface of a router is necessarily on the same subnet as the incoming interface of the ...
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48 views

Layer 2 managed switch and layer 3 switch

If you have layer 2 managed switches which have VLAN's on them, do you still need a layer 3 switch/router?
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2answers
29 views

What is the need for the NEXT HOP coloumn in the routing table when we already mention the OUTGOING INTERFACE in another coloumn?

If the OUTGOING INTERFACE is already mentioned in the routing table, it is natural that the next hop will necessarily be the router attached to the outgoing interface. Then why is there a separate ...
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0answers
26 views

network cutover for remote site from L2 to L3 over IPSec tunnel

I have been trying to cutover one of our remote sites (A) to the new ISP we have purchased. The existing setup is utilizing L2 through another remote site (B) and coming back to the main campus. The ...
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2answers
85 views

Are all packets addressed with the MAC address of the router as they leave the machine?

In the Comptia Network+ All in One, it is said that most home routers have a switch built into them. It is also said that the first thing the router does is strip off any layer two information present ...
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1answer
42 views

Unicast and Multicast MAC address convention

I need help in understanding how Unicast and Multicast MAC address is differentiated as explained in wiki. According to what I understood, when the least significant bit is set as 0 in the first octet ...
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1answer
914 views

difference between switchport trunk encapsulation dot1q and switchport mode trunk

I am new to network engineering and I am currently delving deep into L2 functionality.what is the difference between these two commands: 1 switchport trunk encapsulation dot1q 2 switchport mode trunk ...
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2answers
54 views

Network topology for merging two different layer 2 networks

I have a scenario, (shown in attach diagram) where i need to merge traffic from two server 1 , 2 to target server 3. All three are on different vlans/subnets. With layer 3 switch in between would it ...
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1answer
56 views

Why does the Layer 3 switch drop the ping packet?

I am trying to ping from PC2 (not PC1, there's typo in the picture) to the router's int g0/0, but the packet is dropped at the L3 switch which is along the path. I have tried setting a default static ...
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1answer
35 views

Can use virtual port as the port mirroring's destination port?

Port mirroring can mirror several source port to a destination port(mirroring port). I have several questions about port mirroring. in the dest port, how to differentiate the different source port? ...
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2answers
113 views

Vlan vs. Subnet Broadcast Domain

It is my understanding that Vlans separate broadcast domains, but I often see people say, "subnets define a broadcast domain" as well. Is it correct to say, "Vlans define a L2 broadcast domain, and ...
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3answers
90 views

Using MSTP with RSTP

I have two layer-3 switches connected with two redundant links that I'm trying to run PTP OSPF sessions across, a la: (OSPF) VLAN 1002 - - - - - - - - - - - - / ...
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2answers
39 views

If we already have default VLAN, Why we need Native VLAN? [duplicate]

What is the need of Native VLAN and default VLAN. How they are related? Can Somebody explain this in detail?
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0answers
14 views

Understanding OSI communication model from Electronics Perspective [duplicate]

I have gone through the OSI communication model and the associated levels. But I do not understand on how is this implemented in the Hardware level. Or let me put it like this. Suppose we have a USB ...
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3answers
61 views

How are packets ( received from the server ) sent to the host from the gateway ( which is present in the host network )?

If the host is receiving packets from a server, these packets have a destination IP address of the host and it is first received by the gateway present in the host network. Now the gateway checks the ...
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1answer
80 views

How does a 802.11 (wifi) frame identify the payload's layer 3 protocol?

My understanding is that the 802.11 frame header is an equivalent of ether header. In the ether header, there is an EtherType field that identifies the payload protocol, such as IPv4/IPv6/ARP etc. ...
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1answer
48 views

How do (LANCOM) Tag-Based vlan groups work and on which vlan does the device respond?

I just started a new job and part of it is to manage and maintain the ICT. As the previous network/system engineer left the company i'm on my own to figure out how everything works. I have ...
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1answer
203 views

EXOS layer2 Configure on a Summit x440-G2-24p

I search since Days for a working configuration for a layer2 connection from another extreme switch to this switch. What I connected Physically on my Summit x440-G2-24p: the ethernet(lan) cable from ...
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3answers
354 views

Clarification on when routers encapsulate and decapsulate packets

I'm an application developer working on getting a working knowledge of network engineering, so basically a newbie. I've been trying to figure out exactly when routers decapsulate frames into packets ...
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1answer
136 views

How do computers send switches packets, if switches don't have IP or MAC addresses?

I am new to networking, so please excuse me if I am saying stupid stuff. From my understanding, PCs are sending packets to switches, which then decide which physical port to forward that packet to. ...
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2answers
47 views

Switch Operation Beyond VLAN Segmentation

What are the other operations performed by a switch which are outside the VLAN's boundaries. Is Logical (VLAN) Segregation is exactly same as breaking a switching network physically via a Router?
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1answer
41 views

CRC R bit size to guarantee error free

For a Link Layer frame, it's common to include some bits for redundancy. Suppose we have a frame with X bits of actual data, and want Y bits of error-correction bits. What size do we need to choose ...
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2answers
113 views

Why can't we assign MAC addresses on our own?

Mac addresses are used in networks, not in internetworks. So, why to not create a protocol, that will automatically assign to connected devices MAC address in that way, so they don't repeat in network?...
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2answers
1k views

PPP, Ethernet and PPPoE differences

Correct me if I'm wrong. So, Ethernet technology is being primarily used in LANs. And we use PPP in serial links. To carry IP datagram, we can use either layer 2 technology, such as Ethernet, or we ...
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1answer
58 views

Is an IP broadcast always a layer 2 broadcast also

On my PC I see 255.255.255.255 in ARP with MAC FF:FF:FF:FF:FF:FF, so I'm assuming that in most cases the L3 broadcast is also encapsulated into an L2 broadcast frame, but is this standardized? For a ...
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1answer
62 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 ...
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2answers
754 views

Confusion about data fragmentation/MTUs - why was it introduced in the first place?

I am currently studying networking as a part of my bachelors and I am a bit confused about why fragmentation/MTUs are necessary. In my lecture slides, it only says "Fragmenting if necessary" under the ...
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2answers
106 views

Question about the destination IP inside an IPv4 packet

I'm reading about link and network layers for the first time and I'm trying to put the pieces together to understand how they work together. My question may not have to do with the link layer but I'm ...

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