Questions tagged [ethernet]
For questions relating to Ethernet networking, as defined by the IEEE 802.3 standards.
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When to choose fiber instead of twisted pair (copper)
These days both fibre and twisted pair are supporting 1000BASE-T and 10GBASE-T, but when do you choose one over the other? The obvious one is maximum cable length, but what are other factors which ...
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Why and how are Ethernet Vlans tagged?
I hear about VLAN tagging, but I don’t quite understand the concept. I know a trunk cannot accept untagged packets without configuring a native VLAN, and that access ports only accept untagged ...
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Does having a longer Ethernet cable slow your connection?
As the title suggests, Does a longer Ethernet cable slow your connection down?
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5
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Is Ethernet port blinking really useful?
This question may not look as an important one and in fact it is just out of curiosity.
But to the point:
Is Ethernet port blinking really useful?
Ethernet ports usually have two light indicators ...
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15
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How can I diagnose a bridging (ethernet) loop?
Given that spanning tree has failed (or you don't have any spanning tree) and get an ethernet loop, what's the best way to diagnose where the problem is?
Which switch?, which cable? and so on.
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How does gratuitous ARP work?
Does gratuitous ARP work like a normal ARP request?
Why is gratuitous ARP used for HSRP?
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Why was the MTU size for ethernet frames calculated as 1500 bytes?
Why was ethernet MTU calculated as 1500 bytes?
What specific calculation was done to arrive at 1500 byte ethernet MTUs, and what factors were considered for that calculation?
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What is the actual size of an Ethernet MTU
I think I might be getting confused with terminology surrounding MTU.
This definition from Wendell Odom's CCNA book on MTU:
The IEEE 802.3 specification limits the data portion of the 802.3 frame to ...
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5
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Why are Ethernet Standards written in the form of 10/100/1000? Why not just 1000?
I always have seen Ethernet Standards written in the form "low value/middle value/max value", and always wondered why.
Won't a router just reproduce a lower speeds anything below its maximum if it's ...
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33
votes
1
answer
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Using SNMP to retrieve the ARP and mac-address tables from a switch
I would like to get ARP tables from a switch to a syslog-ng server that has been set up on Ubuntu Server 12.04 LTS. I have read about SNMP and I know the server will act as a manager and the switch as ...
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Why do we still use Ethernet?
There's no doubt the vast majority of Ethernet frames are transporting IP packets. I know there are various other protocols that can be transported over Ethernet as well, but those can be transported ...
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4
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How does a switch learn a switch table?
Say the switch table is empty. If computer A sends a frame destined to computer B, the switch will broadcast asking who has the mac address of B. What if C suddenly sends a frame to A? What is the ...
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Why is 4096 the max value for VLANs
The Tag Protocol Identifier is set to 16 bits.
In the CCNA certification it is said that it's not possible to have more than 4096 VLANs.
4096 in binary is 1000000000000000.
Since 16 bits are allocated ...
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24
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2
answers
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Emulate Ethernet frame loss for testing purposes [closed]
Maybe I am missing something rather basic, but I don't know so I figured I would ask.
In terms of testing, how sensitive various TDMoE are to BER and packet delay, I am looking into how to simulate ...
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What is "industrial ethernet"?
When a teacher introduced it to us he gave the impression that it specifically covers some Siemens technology; that it's even a Siemens trademark.
I believe the term covers something more general, ...
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21
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7
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Introductory level explanation of VLANs
What's the basic use case(s) for VLANs?
What are the basic design principles?
I'm looking for something like a two paragraph executive summary style answer so I can determine if I need to learn ...
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Minimum Ethernet Cable Length?
I have heard from a few people that cables less than 1 meter are prone to transmission problems. Is there any minimum copper cabling length?
Please explain if this is true or not and share any ...
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4
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Why is the CAM table in a switch called CAM table and not MAC table even though it holds MAC addresses?
I know the CAM table in a switch holds MAC addresses and the ports that are associated with the respective MAC addresses. There are no such thing as CAM addresses from my knowledge, so why is it ...
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Jumbo Ethernet Frame Deployment
What are some general guidelines for the successful deployment of jumbo frames in a routed environment?
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6
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Why use IP if we already have a MAC address?
I am preparing for ICND1 exams and recently started to learn about different Cisco devices.
I have just come to know how the packet is generated to be transmitted over a network, or outside the ...
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2
answers
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Ethernet autonegotiation differences between (10M | 100M | 1G) Ethernet
I am studying for CCNA and on Wendell Odom's book is said that(regarding autonegotiation):
When autonegotiation fails on one node, to choose (half/full-duplex) we must use the rule:
If you have a 10/...
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6
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How are IP addresses mapped to MAC addresses?
I've been reading about the differences between MAC and IP addresses, and why we need both of them.
To summarize, MAC addresses are physical unchangeable unique IDs for every single device while IP ...
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3
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Why does an Ethernet cable have four pairs?
I'm curious about why 10Base-T and then 100Base-T Ethernet networks used cables which had four pairs if they only needed two? Were there some cables that only had two pairs?
If we wanted to increase ...
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4
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Are there any reasons to not use BFD?
In looking to implement Bidirectional Forwarding Detection (BFD) it seems to be very flexible in terms of timer tuning, light weight regarding any overhead and it's flexibility in terms of overall ...
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MAC address recycling?
Something I've always wondered about is MAC address exhaustion. Do hardware vendors keep track of MAC address allocation to their platforms, and then subsequently "reclaim" MAC addresses when a ...
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Reason for half-duplex mode in Ethernet?
Half-duplex connections were popular at the time of 10Mbps and 100Mbps Ethernet, and, according to standards, it is allowed also in case of 1Gbps Ethernet.
Am I correct that half-duplex mode support ...
- 1,177
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What's the difference between an Ethernet cable and a UTP cable?
Is there such a thing as an Ethernet cable or technically no? Are they actually called UTP cables?
From wikipedia
UTP cables are found in many Ethernet networks and telephone systems.
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3
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On which layer of the OSI Model does the arp protocol belong? [closed]
Can anyone explain which layer of the OSI model ARP belongs to and which socket it uses?
I referred to lots of books before asking this question.
In some books, Authors are saying that it belongs to ...
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2
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What is the difference between Ethernet II and 802.3 Ethernet?
Can anyone explain to me what is the difference between Ethernet, Ethernet-II and 802.3 Ethernet.
I referred to a lot of books, they are in high level language. Can anyone explain to me in a simple ...
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Why would a switch be connected to a router using three ethernet cables?
In our rented office, we have a router (BT smart hub) connected to a large switch (model unknown). The two are connected using three ethernet cables, thus:
-----------------------
| 1 2 3 4 ...
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16
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3
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How is the root bridge elected in STP?
How does STP/RSTP determine which bridge is the root bridge, and how are paths to the root bridge selected?
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What happens when 2 computers transmits at the same time to a 3rd one in a full duplex switch?
Consider the following scenario:
I have 2 PC's (PC1 and PC2) that wants to transmit at the same time to PC3 in a full duplex ethernet switch. Let's consider that all ports are in the same VLAN, so ...
16
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3
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class-default matches control traffic?
I'm seeing an issue with BFD on a link that's being policed egress where it appears during times where the policer is maxed BFD packets are not getting to the other side. I'm wondering if BFD hellos ...
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How exactly does an Ethernet collision happen in the cable, since nodes use different circuits for Tx and Rx?
I am trying to understand how a collision occurs in Ethernet, especially when a duplex mismatch exists or when on a legacy Ethernet network two nodes transmit simultaneously.
Everyone explains the ...
15
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3
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Configure Cisco ASA in Transparent mode: Layer2 DMZ w/ Vlan translation
I am in the middle of a project to migrate some existing switched ethernet dot1q trunks behind an ASA firewall... these trunks have five vlans each (numbered 51 - 55). This is a simple drawing of the ...
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How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?
I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one:
it looks like a layer 2 packet is limited in size to be much smaller than that. ...
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How does a switch know where to route packet, when there is another switch in front of the destination?
I am just wondering how a switch does know how to route packets to destinations "hidden" behind another switch.
In my understanding a switch has a table that maps each of its hardware ports to exactly ...
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What does the naming convention for Ethernet standards mean: 1000BASE-T, BASE-TX, BASE-SX, etc.? What is the meaning of the components of the name?
I understand the number in the naming convention. The number represents how many Megabits per second can the standard support. However, I do not understand the rest of the naming convention. What do "...
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Does the source MAC address of a frame change when it passes through several switches? [duplicate]
If PC1 sends an Ethernet frame to Switch1 which forwards the frame to Switch2 which in turn forwards the frame to PC2, does any decapsulation happen that changes the source MAC address?
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Troubleshooting low Metro Ethernet TCP throughput
Background
We rented a few layer 2 leased lines, i.e. you have one big pipe at the datacenter and the remote sites have smaller pipes. Inside the layer 2 network you can do whatever you like. Probably ...
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Why does Ethernet use EtherType field to determine what type of packet is in a frame instead of just looking at the packet header?
I'm studying for some networking concepts and have learned that a receiving host looks at an Ethernet frame's header to determine what protocol being used by the packet. It makes me wonder though, ...
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Minimum ethernet frame is 64 bytes, Why the payload must be padded to at least 46 bytes
What is reason to pad payload to mininum 46bytes, to form a ethernet frame of 64 bytes.
Following says min would be 41 bytes.
https://stackoverflow.com/questions/14526139/what-is-the-minimum-packet-...
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Why do I need a crossover cable to connect devices of the same type?
I know that a crossover cable should be used to directly connect devices of the same type and patch cable is used to connect devices of different types.
But I never understood why is it so exactly? ...
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MTU and Fragmentation
Consider the following: NAS with 10G interface connected to 10G interface on switch. Client computers connected to switch via gigabit Ethernet.
Will there be any gain in performance if MTU size is ...
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2
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Is the MTU of Ethernet still 1500 Bytes?
So basically do the modern routers in the internet still use 1500 as the MTU of Ethernet? or the 1500 Byte was for the old days?
What I'm asking here is what is the MTU of Ethernet in modern Networks?...
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Detecting different Ethernet frames
How can someone distinguish between different packets in the Ethernet protocol? It has no "length" field/area as higher-level protocols use to do so.
Because this protocol has handling in both the ...
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3
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What is the purpose of an Ethernet magnetic transformer, and how are they used?
I have been told that Ethernet magnetic transformers are used for base-t Ethernet when transmission is sent over a lengthy cable. What is the purpose of the transformer? (is it for signal filtering or ...
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Switchport in half duplex - Download speed suffering but upload was fine
A user had issues with download speed from the Internet. The connection to the Internet is 100 Mbit/s. The user got around 7 Mbit/s downstream and around 80 Mbit/s upstream.
I tested from my computer ...
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10GBase-T vs. SFP+ Direct Attach
What are the advantages and disadvantages of using 10GBase-T vs. SFP+ Direct Attach to interconnect devices where distance is not a determining factor?
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2
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Shielded Twisted Pair (STP) termination and grounding
I have knowledge terminating CAT5 UTP.
But, for an installation in a remote office, the cable will be routed near a power source which we already know causes a substantial amount of 'noise' on ...
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