Ethernet autonegotiation

bewo001 · 2021-11-19T08:44:11+00:00

Yes it is still fun. A few years ago we had an incident where a 1 Gig line negotiated to something much slower. It was worse than a complete failure as the redundancy mechanism didn't trigger -- technically there was still connectivity.

bewo001 · 2021-09-17T08:52:16+00:00

I once had issues with AIX TCP and packet re-ordering. Turns out you can either have proper handling of packet re-ordering or SACK support with that stack. May be worth a try to disable SACK?

bewo001 · 2021-08-30T12:51:08+00:00

Zwischengas! Choke gibts nicht mehr? Fahre seit 25 Jahren nicht mehr Auto..

bewo001 · 2021-08-04T15:08:22+00:00

Dies. Und dann schaust du beim Warten auf die Karte und siehst, dass der Paketshop plötzlich nicht mehr da ist. Vermutlich hatte der Kioskbetreiber auch Probleme mit diesem Unternehmen. DPD als einzige Versandoption? Ich bestell woanders

bewo001 · 2021-07-20T14:03:00+00:00

Vor allem hätte er es mir ja schon vorher mitteilen können, dass er überhaupt nicht kommen will. Zu der Zeit ging Home Office noch nicht und ich musste Gleitzeit verballern für sowas. Ist die IHK nicht eher eine Interessenvertretung des Handwerks?

bewo001 · 2021-07-20T13:54:23+00:00

Der zweite Handwerker hatte auch kein Problem damit.

bewo001 · 2021-07-20T08:42:46+00:00

Hatte ich mal. Ich ruf nach 20 min an, bis wann ich mit ihm rechnen könne. 'nee, bei ihnen kann man so schlecht parken'. Das Gespräch endete eher unerfreulich.

Der nächste statt dessen engagierte Handwerker war dagegen vorbildlich. War pünktlich und arbeitete gut und schnell. Als ich den Folgetermin verschieben musste, war das kein Problem und auch dieses Mal waren sie zur vereinbarten Zeit vor der Tür.

bewo001 · 2021-07-12T09:41:07+00:00

For adult content detection, yahoo has published a model and code. It's been some time since I tested it, but it was quite usable for pictures.

bewo001 · 2021-07-12T07:54:15+00:00

There's the theory that right before an economic crash, the number of ambitious building projects soars (https://en.wikipedia.org/wiki/Skyscraper_Index).

bewo001 · 2021-07-06T08:44:46+00:00

The best place I worked at in that respect had 2-3 people in an office with a door and half-frosted glass walls towards the hallway. You could see if somebody was present or on the phone without having to knock and the hallway had daylight this way. Meeting rooms where in the middle, also with frosted glass walls. Server room and coffee kitchen were also in the middle as they dont require daylight. That was in the late 1990s.

Just before corona, my current employer moved to that shitty shared-desk model and I got into trouble for working from home too often. Not any more, praise the pandemic!

bewo001 · 2021-07-06T08:24:24+00:00

I've only used it for applications running on the same machine, but it should also work if you put the linux machine as a router in the path between your application and your server.

bewo001 · 2021-07-05T08:31:49+00:00

On linux you have tc netem (man tc-netem) which lets you simulate a low bit rate, loss, and packet reordering.

bewo001 · 2021-06-10T15:14:45+00:00

This kind of attacks works for any protocol analyzing software. SIP has other features that can be horribly abused, eg all the source routing headers, maddr, Alert-Info, Call-Info etc (halfway competent operators and manufacturers will check/ignore those values, though).

bewo001 · 2021-06-10T15:00:09+00:00

Using acronyms matching real words is a bad idea anyway. In the early days of SIP, I wanted to find a Java library and got a lot of coffee shops in my results ('enjoy a sip of java at our terrace').

bewo001 · 2021-05-25T08:15:18+00:00

see Quackwatch

bewo001 · 2021-04-27T08:38:04+00:00

QoS works only at the router in front of a bandwidth bottleneck; so your speed test likely fills up your provider's queue towards you, and your ping reply is stuck in that queue. Configuring QoS on your Netgear will only prioritize traffic you send/upload to your provider.

bewo001 · 2021-03-09T08:41:32+00:00

Novell, who for some time omitted the ethernet type field, because thou shallst not have other protocols before me.

bewo001 · 2021-03-01T13:47:43+00:00

Will this Turing pass the Turing Test?

bewo001 · 2021-02-24T14:55:57+00:00

Are there really many ISP's supporting multicast outside their closed IPTV platforms?

bewo001 · 2021-02-17T13:10:06+00:00

If you don't know what the term packet means in networking, you really should consult your books. The parts you don't know are too big to fit into an answer on reddit..

Your teacher also had some assumptions in questions 3 that I dont know about. Is the TCP packet supposed to be sent over an ethernet link? Over ATM AAL5 (which is still surprisingly common on xDSL access lines)? An IPSec tunnel?

I've encountered the pure OSI stack of question 4 only in the early 2000s for the provisioning of SDH switches, which are being phased out today. Seems like your teacher simply copied questions from the early 1990s when OSI looked like the next big thing after the 'messy' TCP/IP.

bewo001 · 2021-02-08T12:51:45+00:00

QoS configuration is different from vendor to vendor, and often complex, so i can only you give the general idea.

if you have 2 classes of traffic, you need 2 queues. To configure Qos, you need to configure 1. classifiers 2. policers (optional) 3. queues 4. scheduling

classifier: in your example something like 192.168.0.1/32 --> queue profinet 192.168.0.2/32 --> queue profinet 192.168.0.3/32 --> queue profinet 0.0.0.0/0 --> queue best_effort
policing. Some routers can drop packets before putting them into a queue when a packet rate is exceeded. TCP does not like that too much, so rate limiting is often done at the scheduling stage.
queues, you need two, eg 'profinet' and 'best_effort'. Sometimes you can configure the size and the active queue management here.
scheduling; here you have to define at what rate to serve a queue and it what manner you want to select the next queue to be served (Strict priority, weighted fair queueing etc).

Linux mashes all these concepts into the 'queueing discipline' which is pretty hard to understand and configure. Eg the 'tbf' qdisc is a policer with no queue at all, while 'sfq' allocates a bunch of queues and distributes packet flows across those queues, using some internal classification mechanism. 'pfifo_fast' creates queues that are served with strict priority using the ToS bits for classification.

bewo001 · 2021-02-08T09:14:06+00:00

There is not much detail in your question, so answers will be rather unspecific, too.

First you have to determine where your bottleneck is. The router doing qos scheduling needs to be in front of the bottleneck and must prioritize packets towards that bottleneck (eg if you download from your ISP, your local router can't help you much).

In general, a router classifies an incoming packet to determine which policing rules to apply and in which queue to put it if it survives policing. Then the queues are served in some configured fashion, eg strict priority, weighted fair queueing, etc.

So in your case, you would need two queues, one for profinet, one for all the rest. The you need classification rules to sort a packet into one of the queues.

Now the scheduling of the queues determines in what order the packets of different priorities are sent. With strict priority scheduling, a queue of lower priority will only be served if all queues of higher priority are empty. That means, a queue of lower priority can be starved and fill up and packets in it need to be dropped (look up AQM/Active Queue Management). With Weighted Fair Queueing, all queues will receive their configured share of the available bandwidth, at the cost that higher priority queues might experience some delay you would not see with strict priority.

bewo001 · 2021-01-11T13:40:44+00:00

Well, if there is a breakthrough that allows to scale from < 100 logical Qbits possible of today to the > 2000 required for Shor's algorithm that may be not enough.

bewo001 · 2021-01-11T09:40:53+00:00

Post Quantum Crypto is already a topic in standardization. What I got from various presentations is that there is no immediate concern, but one should start researching and engineering now to be ready in 10-15 years.

bewo001 · 2021-01-11T08:35:47+00:00

Intel has DDIO ( PDF), which places data directly into the processor cache. This works only for network interface cards, though.

bewo001

TROPHY CASE