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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 ...
alex.forencich's user avatar
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 +...
Zac67's user avatar
  • 85k
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.
Ron Trunk's user avatar
  • 67.7k
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 ...
Effie's user avatar
  • 1,828
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 ...
Zac67's user avatar
  • 85k
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 ...
Teun Vink's user avatar
  • 17.4k
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ......
richardb's user avatar
  • 1,608
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 ...
Zac67's user avatar
  • 85k
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 ...
Brian Duke's user avatar
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Marc 'netztier' Luethi's user avatar
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 ...
Zac67's user avatar
  • 85k
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 ...
Zac67's user avatar
  • 85k
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, ...
Zac67's user avatar
  • 85k
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. ...
Sage's user avatar
  • 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 ...
Zac67's user avatar
  • 85k
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 ...
Jeff Wheeler's user avatar
  • 5,493
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 ...
Zac67's user avatar
  • 85k
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 ...
OzNetNerd's user avatar
  • 2,337

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