Questions tagged [layer2]
For questions about the OSI layer-2 (data-link layer).
1
vote
1answer
157 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
460 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
386 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
812 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
13 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
52 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
60 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
89 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 ...
1
vote
2answers
53 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 ...
2
votes
1answer
136 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
41 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
60 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
39 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
129 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
454 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
48 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
258 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
30 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
399 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, ...
4
votes
1answer
285 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
248 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
156 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
280 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
60 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 ...
5
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
430 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 ...
4
votes
2answers
66 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
57 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
405 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
278 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
39 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
42 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
75 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
268 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
132 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
115 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 ...
1
vote
3answers
89 views
Can Ethernet II frame's Type be Layer1's or Layer4's protocol?
The Ethernet II frame's Type field can be IPv4, ARP, so it can be Layer2 and Layer3's protocol.
This is a snapshot of frame captured by WireShark.
But I have a question, whether it can be other ...
2
votes
2answers
657 views
Connecting Layer 2 switchport to layer 3 port
I have a config that I am trying to bring up, and in my mind it should work, but perhaps I am missing something.
The idea is that one end of the link is a layer 3 interface on a router. The other end ...
0
votes
2answers
96 views
Layer 2 Routing between subnets and VLANS [closed]
I am studying for my Networking exam and from what I have pieced together from other posts on here is this. Please correct me if I'm wrong:
Layer 2 switches can only route packets between different ...
1
vote
1answer
34 views
Separate network for test systems
I often read that you should put customer machines into a separate (testing) network like a DMZ.
Is a layer 3 device (switch/router + firewall) a good option for this? Since some ports need to be ...
5
votes
2answers
150 views
Why is RTS/CTS optional for IEEE 802.11?
In wikipedia it is stated:
Request to Send (RTS) frame: The RTS and CTS frames provide an optional collision reduction scheme for access points with hidden stations. A station sends a RTS frame as ...
0
votes
2answers
137 views
Slotted Aloha Protocol divides up time into slots, each slot corresponding to one frame. Is this same TDM?
Slotted Aloha Protocol divides up time into slots, each slot corresponding to one frame. Is this the same as Time Division Multiplexing (TDM)?
3
votes
5answers
441 views
Is there a Layer 2 address advertising protocol?
I needed help in understanding if LLDP/CDP is the Layer 2 equivalent to RIP or say any Layer 3 route advertising protocol. If not,is there a protocol that advertises the MAC Address Tables among ...
1
vote
1answer
371 views
Routing and Bridging on a Layer 2 or Layer 3 device
The thing that intrigues me is, say I have a router and I configure it’s interface as a Layer 2 and have 2 Vlans on the same router. So if I want to transfer the data from one Vlan(say VLAN-10) to ...
4
votes
1answer
852 views
Do we send ack frames in ethernet? if not then how does a router know if its neighbors are down or not?
So first off, do ethernet sends ack frames or not?
if it doesn't : then how does a router know whether its neighbors are down or not?
if it does : then is it cumulative ack with an ack timer or one ...
1
vote
1answer
121 views
Frame transfer from one switch to another configured with VLANS
Hi,
My question is related to the Vlan. And this question would consist of 2 parts.
1)Would Switch 1 know all the devices present in Vlan 2 or Vlan 3, including the ones present in the Switch 2.
...
0
votes
1answer
53 views
How to show all data (bitstream with preamble, SFD) on Ubuntu with an Intel Ethernet Interface?
On my PC I have an Intel Ethernet Connection I217-LM with e1000e driver.
If I receive packets in Wireshark or any libpcap based tool, the received ethernet frames start with Ethernet II frame and end ...
1
vote
1answer
125 views
Why are Frame Relay, ATM and MPLS called “Layer-2 VPN”?
A VPN results, when two physically separate networks become virtually one bigger network.
But Frame Relay, ATM and MPLS don't do that, they just connect two network, but they don't unify them.
So ...
