Questions tagged [layer2]

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

Filter by
Sorted by
Tagged with
0
votes
2answers
89 views

Different MAC addresses [on hold]

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
42 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?
3
votes
3answers
432 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 ...
1
vote
2answers
70 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
67 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 ...
2
votes
2answers
587 views

How can we identify layer two device in a network or what are those device effects on a frame

This is sample of a traceroute to google.com: TraceRoute from Network-Tools.com to 216.58.194.46 [google.com] Hop (ms) (ms) (ms) IP Address Host name 1 0 0 0 ...
4
votes
2answers
1k 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 ...
3
votes
1answer
29 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
225 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 ...
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
489 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 ...
1
vote
1answer
176 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 ...
5
votes
2answers
814 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 ...
5
votes
2answers
183 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
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
59 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
69 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
95 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
1answer
235 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)...
2
votes
4answers
999 views

Should I receive an ARP reply from a host that is logically on a different subnet but is connected to my host via a hub?

Host A: 128.238.66.100/16 Host B: 128.238.67.100/24 The hosts are connected to the same hub and nothing else is connected to that hub. The routing and ARP tables of both hosts are empty. Host A ...
1
vote
1answer
43 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
83 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
45 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
204 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
499 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
60 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 ...
0
votes
1answer
301 views

Layer 2 ARQ protocols

Some authors (i.e. Tanenbaum, Stallings) reference ARQ protocols as layer 2 mechanisms for handling errors. Even this page from Wikipedia says that these protocols reside in the Data Link or ...
4
votes
2answers
353 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? ...
3
votes
2answers
9k views

Mac address and IP address in physical addressing in Data-Link layer

Framing is done in Data-Link layer. We give physical addresses there. Destination address, source address and MAC. If two PCs in different networks, we try to sent data from one another, we specify ...
-5
votes
4answers
737 views

IP Address and Layer 2

As per my Knowledge MAC address is required to communicate two machines...and on layer 2 (Switch) can't understand IP (if i am right)....suppose we have 2 systems (Sys1 and Sys2) with 2 different IP ...
7
votes
4answers
4k views

Why preamble is not considered a part of the Ethernet Header?

If I search where does my data start in an Ethernet frame, I get a common answer which says TCP header( 20 bytes) + IP header ( 20 bytes) + Ethernet header( SA + DA + Type) i.e 14 bytes. So, in short ...
3
votes
4answers
144 views

Need of routers and IP addresses

I dont know if my research is enough or not but I could not find answers on the net. My question is why not use bridges instead of routers. We know bridges can connect two different networks. Using ...
4
votes
1answer
928 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 ...
2
votes
1answer
553 views

Bridging networks without NAT: how it's done?

I have quite limited networking experience, so probably i'm asking about very simple things. I'm reading about linux bridge interfaces, and documentation states that there is no NAT by default and ...
1
vote
2answers
202 views

Why Ethernet was chosen to be the primary protocol + why carrier ethernet was created?

I'm currently trying to investigate the extra benefit that Ethernet has to offer for the internet today. As far as i investigated & know, Ethernet gives us a new hardware, cables and functionality ...
7
votes
4answers
204 views

Is ethernet a term describing just the protocol or the interfaces also?

Is ethernet describing the protocol and therefore cat5 cables became labelled ethernet cables because they are used for this protocol?
4
votes
3answers
529 views

What practices/ mechanisms/ protocols can be used to secure communication on physically exposed Ethernet links?

Given that Ethernet cables are everywhere and use for all kinds of links and it is assumed they are physically guarded, hence typical installations do not leverage any "secure" mechanisms. Let's say ...
1
vote
2answers
31 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
1answer
1k views

How does priority work in token ring?

Token rings have an optional priority feature, for which the 8 access control bits in the token ring non-token frame are used. Suppose we are working with the delayed token reinsertion scheme. How ...
1
vote
1answer
205 views

DTP mode desirable and on

the on mode still negotiable (send/receive DTP) until i set it no negotiate so what is the Difference between on and Desirable. please give an example :))
6
votes
2answers
402 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, ...
3
votes
1answer
2k views

Routing of 2 Gateways via a Layer 2 Switch

Please refer to the network diagram below, it is a very simplified version of an actual network installation. The Router has 3 Vlans, OSPF has been configured and all the 3 vlans have been added to ...
4
votes
3answers
508 views

'interface vlanX' or 'interface loopbackX'

VLANs are a layer 2 concept. We can all agree on that but why, then, do we use the 'interface vlanX' to allow routing on a switch. If we want to setup a default gateway for VLAN X on a Layer 3 switch ...
1
vote
3answers
803 views

Routing between two networks

I had a question here. Basically, we have two different networks. Each network has one Cisco 2960 layer 2 switch for each network in the same location. These are two individual networks. There is a ...
1
vote
2answers
1k views

ARP spoofing in different VLAN

I want to know if I'm protected for ARP spoofing. In my network, all PCs, printers, phones and servers are in distinct VLANs. I got a layer 3 switch for servers, which handles routing between these ...
1
vote
2answers
2k views

Switching vs Routing

I have seen quite a few discussions regarding MPLS stating things like: MPLS combines the performance and capabilities of Layer 2 (data link layer) switching with the proven scalability of Layer 3 (...
4
votes
1answer
76 views

How does Junos distinguish that route is learned in Layer 3 or Layer 2 VPN environment?

As I understand from Understanding Junos OS Routing Tables document, then bgp.l3vpn.0/bgp.l3vpn-inet6.0 or bgp.l2vpn.0 tables contain routes learned from other PE routers in Layer 3 or Layer 2 VPN ...
3
votes
1answer
209 views

Consequences of an intra-switch Loopback cable

I am using Dell switch and I looped it to itself. If I enable STP on 2 ports, what happen the port states? I have attached the topology below. Let me know, if you need clarification.
1
vote
1answer
924 views

Relation between Ethernet and 802.11 headers

I would like to ask about the relation between 802.11 and Ethernet L2 Link layer. Are they dependent of each other? Or can they be seen as independent L2 link layers (with only similarities in ...