Questions tagged [layer2]
For questions about the OSI layer-2 (data-link layer).
349
questions
0
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1answer
31 views
Why or when do we need Layer 2 NAT? [closed]
What is the point of public addresses in Layer 2? Why or when do we need it? When is it healthy to use? Or is it even a common thing?
Sorry I am kinda new at networking and I just googled it but ...
0
votes
1answer
25 views
Does the length of a frame influence the likelihood of a collision?
Considering two separate analog signals on the same frequency transmitting digital data that represents a frame, from my understanding if any portion of the two signals overlap, this is a collision.
...
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0answers
29 views
Logs on my Cisco ASA show the public gateway (ISP router) is pinging the internal network, how? [closed]
Im (remotely) working with an issue where the network has intermittent drops. i suspect possible routing loop, but havent confirmed that yet.
In the logs of our Cisco ASA 5506, i see that the public ...
0
votes
1answer
49 views
Does a router work both on Layer 2 and Layer 3? [duplicate]
According to TCP/IP model router works at Layer 3. But when data has to be transmitted to different network it is based on IP address but hop-to-hop transmission is based on MAC address.
That means ...
0
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1answer
26 views
Passing Modbus TCP/IP nodes (connected in multiple VLANS, same network) via Toffino firewall
I have been assigned to check the security aspect of the below network shown in image.
When i asked question on security of individual modbus device, I was told to create individual vlans for each ...
3
votes
2answers
392 views
Why the two connected routers via PPP doesn't use ARP but ethernet use 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, ...
1
vote
3answers
125 views
Is there a ping equivalent on layer 2?
You can use ping to measure RTT between you and an IP host and thereby confirm connectivity. Is there an equivalent that can be used on L2/Ethernet with MAC addresses?
i.e. l2ping AA:BB:CC:DD:EE:FF
(I ...
0
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2answers
172 views
How is P actually chosen in P-persistent CSMA?
I am struggling to understand how the probability value P is chosen for P-persistent CSMA for any particular station, what's the logic behind this.I have read from Wikipedia .
P-persistent
This ...
0
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1answer
25 views
Does creating frames done by device drivers?
If I got it right, TCP and IP packets are created normally by software running in the
kernel. So when I as a user open up a socket of type TCP/IP and send a message, the kernel takes care of all those ...
2
votes
1answer
28 views
Avoiding FPCs rebooting during RE switchover on Juniper EX8200 Switche
We have Juniper EX8208 chassis based switch running in a production environment. The switch has 2 REs running in active and standby role with RE0 being the primary routing engine. The device is ...
1
vote
1answer
83 views
IGMP in multiple switches with multiple Senders and Receivers in same VLAN
I am trying to send multicast traffic from 3 Senders to corresponding Receivers in same VLAN (100) spread across 3 switches.
I setup a Querier in one of the switch, but it doesn't seem to forward ...
1
vote
2answers
69 views
What layer 2 encryption can I run over a leased line with the underlay (MP-BGP with MPLS on top if it)?
My company has its branch sites connected to HQ using Ubiquiti airFiber24 HD.
The company wants to acquire a leased line fiber connection to branch sites.
We want to run our own encryption on top of ...
0
votes
1answer
75 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 ...
0
votes
3answers
126 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 ...
1
vote
0answers
49 views
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 ...
0
votes
2answers
60 views
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 ...
1
vote
4answers
105 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 ...
0
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0answers
22 views
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 ...
0
votes
2answers
40 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 ...
0
votes
3answers
73 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 ...
1
vote
1answer
80 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 ...
1
vote
2answers
57 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 ...
0
votes
1answer
31 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 ...
0
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2answers
36 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---...
10
votes
3answers
2k views
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 ...
1
vote
1answer
96 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 ...
3
votes
2answers
575 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 ...
6
votes
2answers
2k 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?
1
vote
1answer
160 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 ...
2
votes
1answer
134 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 ...
0
votes
1answer
30 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 ...
1
vote
2answers
72 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 ...
0
votes
0answers
22 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 ...
0
votes
2answers
72 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.
...
0
votes
0answers
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 ?
0
votes
1answer
30 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 ...
2
votes
2answers
996 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 ...
2
votes
2answers
70 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 ...
0
votes
1answer
42 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 ...
1
vote
2answers
84 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 ...
0
votes
1answer
76 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 ...
1
vote
3answers
245 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 ...
0
votes
1answer
35 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 ...
0
votes
3answers
117 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 ...
0
votes
1answer
47 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 ...
0
votes
2answers
52 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 ...
1
vote
2answers
103 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?
1
vote
1answer
41 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?...
0
votes
2answers
248 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 ...
1
vote
3answers
1k 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 ...
