8
votes
Accepted
In Cyclic Redundancy Check, how does the receiver knows what the generator polynomial is?
It's true that you have to know it in advance in order to calculate the CRC.
The correct polynomial depends on the application of the CRC. For Ethernet, for example, the CRC-32 polynomial is part ...
- 67.1k
6
votes
What is "collision domain"
This will be a bit of a layman's answer, rather than quoting spec, but it should be accurate.
The collision domain is the sum total of the network segment (hosts, hubs) affected by the collision, and ...
- 236
4
votes
Accepted
Why are there error detection methods in almost every layer of a network?
If a packet gets corrupted on the wire, then the Ethernet FCS should catch that. However, many switches and routers will strip off the FCS, route the packet, and then compute a new FCS. If the packet ...
- 493
4
votes
How often does it happen that at the Layer 2 (MAC) an error goes undetected?
Ethernet layer 2 doesn't correct errors, it only detects them by frame check sequence (FCS). The algorithm for FCS is CRC with the polynomial G(x) = x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 +...
- 82.7k
4
votes
Why I’m getting overlaps with fast Ethernet 0/1 when assigning an ip
You can't have two interfaces on the same subnet. In your case, you're trying to put both on 192.168.10.0/24. You'll have to choose a different subnet for one of them.
- 67.1k
3
votes
In determining the Hamming distance, how does one know what the list of valid codewords are?
you have to design a code that defines what the valid list is (or how valid code words should be computed). This usually works by having your code insert some additional bits into the data, so that ...
- 1,828
3
votes
Accepted
Resource Errors on 1G interfaces in Juniper router
According to this juniper document it is the sum of transmit drops. This Juniper forum post explains it a bit more:
Basically, when a packet cannot be either put in the buffer or retrieved from the ...
- 17.1k
3
votes
Cisco nexus CRC error on interface
An interface running at 20 Gbit/s processes between 1.6 and 30 million frames per second or 100 to 1800 Mframes per minute.
One FCS error/min corresponds to a bit error rate of .8x10-12 which is ...
- 82.7k
3
votes
Accepted
Physical layer errors in Ethernet
For the specific case of 100BASE-TX and the 100Mbps MII interface: there is a receiver signal RX_ER.
The Physical Coding Sublayer (PCS) specification says:
24.2.2.1.7 Invalid code-groups
......
- 1,578
3
votes
Layer 2 error correction
How are acknowledgement sent at data link layer to the sender when crc
of frame is incorrect?
That depends on the Data-Link protocol, but most Data-Link protocols simply drop bad frames. For ...
- 98.8k
3
votes
What is "collision domain"
Well, I see your question as "What is a collision domain". In simple terms, a collision domain, like the name suggests, is an area where collision can occur. Think of it as a narrow tunnel where space ...
- 429
3
votes
What is "collision domain"
A collision domain is all devices connected by shared medium. Originally a collision domain was a physical cable, then repeaters and hubs were added. The shared medium ended at a router port and was ...
- 131
2
votes
Why are there error detection methods in almost every layer of a network?
You didn't specify what protocol or media TCPs running on in your case, but assuming IP, the checksums calculated by the sender and checked by the receiver only verify the packet headers, not the pay ...
- 217
2
votes
Why are there error detection methods in almost every layer of a network?
Remember that each layer is independent of every other layer, and the original design of each protocol in a layer is that my layer cannot depend on your layer doing any error detection, or the error ...
- 98.8k
2
votes
Accepted
User Datagram Protocol (UDP) protocol can error control?
UDP itself has no mechanisms for neither flow control, nor congestion control, and no error correction. If the application's datastream needs any of these, then they must be implemented within the ...
- 8,826
2
votes
Accepted
Layer 2 ARQ protocols
Ethernet's link layer uses CRC32 in the Frame Check Sequence field, trailing the payload data. If FCS fails the frame is dropped. Other reasons for dropping a frame include link congestion, QoS, ACL ...
- 82.7k
2
votes
CRC R bit size to guarantee error free
A CRC in general isn't well suited for error correction, just detection.
Any redundancy you add to an original data block is limited in the amount of errors it can detect (or correct).
Any practical ...
- 82.7k
2
votes
Accepted
Troubleshooting network issues; General inquiry
There is no common cause for that problem. Possible problems include cabling, especially with PoE, a defective device or switch port.
autonegotiation sometimes results in 100mbit full duplex but is ...
- 82.7k
1
vote
Accepted
In determining the Hamming distance, how does one know what the list of valid codewords are?
how do we even know what the list of possible codewords even are to begin with?
The valid codewords are defined by the line code implementation, they are agreed upon by all users. For Ethernet, ...
- 82.7k
1
vote
Accepted
CRC errors in DC, ruled out L1 issues
I wanted to post that the problems suddenly disappeared. It came back for a few days after my comment on May 21, but now it is gone since around May 24. It must have been some sort of external source. ...
- 21
1
vote
Accepted
How does the Ethernet handles start of frame collision?
Any kind of signal that is transmitted concurrently to another signal causes a collision (in half-duplex mode).
You need to understand that the signal on the medium is analog, not binary. So, on ...
- 82.7k
1
vote
Cisco nexus CRC error on interface
Have you got errors on any other ports? The Nexus switches in your diagram operate in cut-through mode by default, and packets larger than ~768 bytes can be forwarded even if they have errors. This ...
- 5,449
1
vote
Intermittent issues on a dark fibre point to point link
302323 input errors, 302323 CRC, 0 frame, 0 overrun, 0 ignored
I think this is the key information. Apparently, the fiber from the 2960 transmitter to the 3650 receiver is very bad. If you've already ...
- 82.7k
1
vote
cisco Total output drops on interface
Have you noticed a degradation in performance since doing the upgrade? If not, the issue could be that you have been experiencing the issue all along but your previous IOS version wasn't reporting the ...
- 2,337
1
vote
Underruns in ASA interface
as stated in https://supportforums.cisco.com/discussion/10780211/help-underrun-errors : underruns occours when rx-ring is full (unable to accept more pkts); it mean that NIC is unable to pass data to ...
- 51
1
vote
How can I test my ping application for proper detection of ICMP return types and codes
Take a look at scapy: http://www.secdev.org/projects/scapy/ and tcpdump/wireshark. With the former you can generate any ICMP packet, with the later you can see what your generated packets look like.
...
- 656
Only top scored, non community-wiki answers of a minimum length are eligible