- Welcome to Networking-Forums.com.
We're Here to Help!
Recent posts
#1
Forum Lobby / Re: old Cisco hardware value
Last post by icecream-guy - August 18, 2025, 06:26:09 AMI got 30 bucks (US) a the recycle center for a bunch of old gear and a box of cables.
#2
Forum Lobby / Re: old Cisco hardware value
Last post by deanwebb - August 05, 2025, 11:21:04 AMI recycled my old gear. Getting 50 bucks and postage wasn't worth lugging it around and trying to ram it into a box.
#3
Forum Lobby / old Cisco hardware value
Last post by icecream-guy - August 03, 2025, 06:36:30 AMdoes old cisco hardware have any value anymore, 2900 & 3550 switches, 3600 routers? or is it time for the electronics recycle? I see maybe 50-60 bucks on ebay. but there are a ton.
#4
Homework Help / Re: Computing CRC (used to fee...
Last post by deanwebb - July 22, 2025, 08:32:06 AMWell, time for me to do a deeper dive into CRCs...
In networking, the CRC is typically calculated on the fly as the data goes out of the network interface and is added to the end of the transmission. There is a SHA checksum with the data that is actually used to check for data integrity, so the CRC in networking is for the datalink to determine if there are any bit errors. CRC itself is too lightweight to do a proper integrity check, which is why the SHA checksum is included with the data set proper.
In environments with low to non existent error rates, CRC can be seen as redundant, especially with TCP data being sent with a SHA checksum on it. In operational technology (OT) environments, however, where the gear is thinly provisioned and data transmission is a priority, the CRC is used on the OT protocols as a quick and easy way to determine if the data arrived completely or if a retransmission is required.
For your case, the maths are by the sending system. Honestly, it does not matter what algorithm is used, so long as it's the one for the protocol being transmitted. Humans do not calculate CRC.
The data, 1010, will be manipulated until the system gets 0 and a remainder. The remainder are the CRC bits.
https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Computation shows a sample calculation.
But in the real world, we don't look at the CRCs. We *will* look at CRC error rates on a device and, when they get too high, will consider corrective action on the hardware or connecting media.
In networking, the CRC is typically calculated on the fly as the data goes out of the network interface and is added to the end of the transmission. There is a SHA checksum with the data that is actually used to check for data integrity, so the CRC in networking is for the datalink to determine if there are any bit errors. CRC itself is too lightweight to do a proper integrity check, which is why the SHA checksum is included with the data set proper.
In environments with low to non existent error rates, CRC can be seen as redundant, especially with TCP data being sent with a SHA checksum on it. In operational technology (OT) environments, however, where the gear is thinly provisioned and data transmission is a priority, the CRC is used on the OT protocols as a quick and easy way to determine if the data arrived completely or if a retransmission is required.
For your case, the maths are by the sending system. Honestly, it does not matter what algorithm is used, so long as it's the one for the protocol being transmitted. Humans do not calculate CRC.
The data, 1010, will be manipulated until the system gets 0 and a remainder. The remainder are the CRC bits.
https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Computation shows a sample calculation.
But in the real world, we don't look at the CRCs. We *will* look at CRC error rates on a device and, when they get too high, will consider corrective action on the hardware or connecting media.
#5
Homework Help / Re: Computing CRC (used to fee...
Last post by networkloser - July 22, 2025, 06:55:43 AMThere are things like C(7,4), CRC-8, different representations.
#6
Homework Help / Computing CRC (used to feel si...
Last post by networkloser - July 22, 2025, 06:55:17 AMNow, I'm absolutely unsure why is CRC giving me a headache. 
Say I've this data to be sent with CRC:
1010
Now, I need CRC bits for this. Fourouzan and Kurose Ross book are too dense for me currently. Can anyone share some insightful materials to learn this? Something easier for my brain.
Grateful to any kind of help. Chatgpt and deepseek seems to be in what direction they have no idea
Say I've this data to be sent with CRC:
1010
Now, I need CRC bits for this. Fourouzan and Kurose Ross book are too dense for me currently. Can anyone share some insightful materials to learn this? Something easier for my brain.
Grateful to any kind of help. Chatgpt and deepseek seems to be in what direction they have no idea
#7
Homework Help / Re: How did Dijkstra's reach t...
Last post by deanwebb - July 14, 2025, 11:18:20 AMTo find the answer, I found this: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
And it's a fun little article about how Dijkstra thought it all out and made the algorithm. There is a step-by-step calculation that runs until one of the calculated paths reaches the destination. That first path is therefore the shortest.
The algorithm also works, with modifications, to present ranked-choice alternatives to the shortest path, should it become unavailable or degraded.
Other shortest-path solutions are discussed here: https://en.wikipedia.org/wiki/Shortest_path_problem . Solutions don't necessarily fail, but are rather perhaps better for some applications than others.
And it's a fun little article about how Dijkstra thought it all out and made the algorithm. There is a step-by-step calculation that runs until one of the calculated paths reaches the destination. That first path is therefore the shortest.
The algorithm also works, with modifications, to present ranked-choice alternatives to the shortest path, should it become unavailable or degraded.
Other shortest-path solutions are discussed here: https://en.wikipedia.org/wiki/Shortest_path_problem . Solutions don't necessarily fail, but are rather perhaps better for some applications than others.
#8
Homework Help / How did Dijkstra's reach to si...
Last post by networkloser - July 14, 2025, 02:19:34 AMIs there a history of attempts to write a shortest path algorithms? And how they failed? What was their thinking process. I am currently learning about link-state routing and I am unable to figure out centralized dijkstra's algorithm even after being stuck in screen/textbook for lots of hours. It is extremely overwhelming to me. Thus, if I could get ideas on why the algorithm was exactly made, why was it chosen for routing purposes, and stuffs like that, that'd greatly be of benefit to me.
#9
Homework Help / Re: Trying to understand scena...
Last post by icecream-guy - July 11, 2025, 09:08:31 AMyes but need a few more on ramps down the mainline.
#10
Homework Help / Re: Trying to understand scena...
Last post by networkloser - July 11, 2025, 06:31:58 AM
You mean something like this, right? I am learning slowly.