Questions tagged [layer2]
For questions about the OSI layer-2 (data-link layer).
249
questions
0
votes
0answers
19 views
Confusion regarding byte count method of framing [closed]
I am trying to understand the concept of Byte Count framing method. I've understood about what it does and what is the issue with it. But there's a part which I still cannot comprehend. Consider the ...
0
votes
3answers
59 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
votes
2answers
262 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 ...
0
votes
1answer
20 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 ...
1
vote
1answer
50 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 ...
0
votes
2answers
96 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 ...
2
votes
1answer
43 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?
1
vote
2answers
86 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
votes
3answers
92 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:
...
0
votes
1answer
75 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 ...
3
votes
1answer
33 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
votes
2answers
229 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
vote
1answer
192 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
votes
1answer
543 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
votes
3answers
461 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
votes
2answers
817 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 ...
0
votes
0answers
14 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
votes
1answer
62 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 ...
0
votes
1answer
76 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
votes
2answers
110 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
votes
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
votes
1answer
346 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
vote
1answer
47 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
votes
1answer
113 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
53 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
votes
3answers
327 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
581 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
65 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
468 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
vote
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
405 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
354 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
419 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
210 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
592 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
99 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
479 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
71 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
61 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
419 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
432 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
41 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?
0
votes
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 ...
2
votes
2answers
44 views
Can Multicasting be duplicated by broadcasting on a subnet?
Is there any functional difference between:
A) Broadcasting to a range of addresses
B) Putting the range of addresses into a subnet and broadcasting to that subnet
Would it matter if there was a ...
2
votes
1answer
136 views
Layer 2 error correction
How are acknowledgement sent at data link layer to the sender when crc of frame is incorrect?
1
vote
2answers
389 views
BGP with x2 sessions and x2 L3 VLANs - Please Explain
I am learning about Cisco BGP networking now and came across an interesting situation. In my examples, there was one which suggested that two VLANs were configured on Layer 3 in order to run two BGP ...
1
vote
1answer
205 views
Layer 3 switch model 3950 encapsulation
How to ensure trunk link in the switch are using dot1q encapsulation, when dtp (dynamic trunking protocol) is enable along with vtp.
I know when manually setting trunk links, you can force the trunk ...
1
vote
1answer
23 views
Protocol Identification
At the data link layer, many protocols run simultaneously, or one after other, right? my question is how date link layer knows about which layer 2 protocol to run and at which sublayer?
1
vote
3answers
131 views
Why do clients request a MAC via ARP, if the router knows the local LAN's MAC addresses already?
If I have an infrastructure type network, why does a local PC send out an ARP request for a MAC? Doesn't the router know the MAC addresses already, since it is using at least Layer 2?
Does it do ...
