Questions tagged [layer2]

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

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33 views

Does a router have multiple DLLs inside?

I came across a practice question of true/false answer type . The statement is: "A router has single network layer that will interact with 2 Data link layers" . Ans:True (no explanation ...
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3answers
86 views

No internet access on VLAN

I'm trying to setup VLAN on my TL-SG3210 (3.0). I created simple VLAN: vlan 10 name "vlan10" Then, I assigned port 2 & 3 to VLAN. I also created interface: interface vlan 10 ip ...
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What are non-learning and learning VLANs?

I was going through some IEEE standards for switches (IEEE 802.1aq and IEEE 802.1Qca), and came upon a terminology of learning and non-learning VLANs. I read that learning VLANs are used in Shortest ...
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How do layer-2 devices (bridges/switches) join a multicast MAC address?

I was going through the IEEE 802.1Q (2018) standard on my own. The standard speaks about group addresses, and how these group addresses are learned by transit bridges, which is all fine. But how do ...
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4answers
86 views

Do layer 2 protocols allow hosts to communicate without being on a network?

Please go easy on me as I'm just a noob in the networking space. As far as I have learnt, layer 2 protocols use MAC addresses for communication, which doesn't really depend on what network you're in ...
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How is it possible that CSMA/CA works in areas with a lot of users within a small radius (e.g. rallies, concerts, etc.)?

My understanding of CSMA/CA is that devices listen until a Wi-Fi channel is idle before sending packets. If a collision still happens, then the devices waits a random interval before attempting to ...
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2answers
37 views

Is there a layer 2 protocol that can be used to send arbitrary data?

I would like to design several devices that receive simple commands from a single controller device all residing on the same layer 2 switch. Is there a protocol that allows me to do this without ...
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3answers
65 views

Is it possible to have a local area network with only layer 1 and not layer 2 of the OSI model?

I know the OSI model has seven layers. Can you consider a LAN to exist without layer 2 and just layer 1? The answers that I saw on Quora were not clear. Some of the answers on Quora came close to ...
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1answer
55 views

100BaseTX Ethernet Idle code (“/I/”) 4B/5B origin

While searching how the PHY LINK status is determined, I stumbled across this answer : In 100BaseTX Ethernet, link pulses aren't used, but instead, link status is detected and maintained via the ...
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2answers
42 views

Proxy-ARP when the destination device is connected to the same layer-2 switch, but belongs to a different subnet

I have recently learned about Proxy-ARP and am slightly confused about what would happen in the following scenario. Let's say I have two host devices A (IP: 10.0.0.10/24) and B (IP: 10.0.1.10/24) that ...
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25 views

Routing switches at core and distribution

My employer has your standard 3 layer architecture, however they want both core and distribution routing and switching. This is so that some networks are routed, and some use only layer 2 between ...
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32 views

Tagging a Vlan across routers

I'm usually against tagging a VLAN across a router, as to not incur issues with spanning tree. My company is asking the following PLC --Vlan72-- SwitchA --RouterA---CoreRouter---RouterB---...
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Why does PPP need an underlying protocol?

The Point-to-Point Protocol is (at least according to Wikipedia) a Datalink Layer Protocol. I know that different use cases exist for it but on examining the image below from Wikipedia one can see ...
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1answer
65 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 ...
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2answers
346 views

Capturing LACP PDUs in an aggregated link on Juniper MX

We need to capture LACP PDUs on a member link of an aggregated bundle link on Juniper MX connected with other router via DWDM link and save the output in .pcap format using write-file knob. Can ...
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1k views

How do I know the switch is layer 2 or layer 3?

Is it possible to find the switch is Layer3 or Layer2 in (Switch)CLI? Is there any command to check whether the switch Layer(Layer 3 or 2) in CLI?
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1answer
108 views

Transporting an Ethernet Port in a LDP Based VPLS Instance on Juniper MX routers

We are currently transporting an Ethernet Port using LDP Based Layer 2 VPN service (P2P PW) in Juniper MX.This P2P LDP PW is up and currently working. Below is the configuration against this:- set ...
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1answer
105 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
29 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
54 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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19 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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64 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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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
29 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
699 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
50 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
34 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
66 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
59 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
190 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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32 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
80 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
44 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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45 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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2answers
86 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
36 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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147 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
615 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
266 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
77 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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70 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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36 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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27 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
218 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
131 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
10k 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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155 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
95 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
38 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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378 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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