Author: flipaoXIX

BFD Multihop

BFD is a protocol that I assumed I knew “well” as it is quite straightforward…. But after having to check how to configure BFD multihop works I notices, I had actually no idea. As usual, I need to read the RFC at some point.

From this link, I noticed that the concept of Hellos and Echo…. and that echo uses the same IP as src and destination…. I really like the wireshark captures.

Copy/Paste from the link

Packet Types

Control Packets

Control packets are used to establish BFD peerings. Essential information are included within these packets, to include flags for things such as authentication, in addition to the timer negotiations. 
These packets are send via UDP to the destination of the far side IP, utilizing the bfd-control port of 3784. 
Because these packets must actually be processed by the peer, they are sent less frequently then the actual BFD echos used for sub second failure detection.


Echo Packets

BFD echo packets are essentially for local use. They are sent with the same source, and destination IP of itself, destined for the UDP bfd-echo port of 3785. When an echo packet is received, because the destination IP is not of the router receiving it, it simple forwards it out of the appropriate interface, ridding the need to punt it up to the processor.
Because the source and destination IP are the local router, BFD can be ran asynchronous. As in, you can set up a single side to utilize BFD echo detection, while the other side merely maintains a BFD neighbor relationship through control packets.

And now about the BFD multihop. It is a short read, and main point is the UDP port is 4784 compared with 3784 in single-hop.

Then checking for the specific details for configuring BFD MH in NX-OS, it is better to check the official documentation. That for example confirms “Echo mode is not supported for multihop BFD.”

Another thing to take into account is the COPP. You need to check if your device OS captures BFD in the CoPP policies as multi-hop goes to CPU. As well, check if there is any other hardware configuration required.

Another thing that bites me is that when testing this in a software lab, BFD is always down but at least the routing protocols come up.

NVIDIA GTC March 2023

I watched this week some interesting videos from NVIDA GTC related to networking. And it is a pain that you need to use a “work” email to register….

  • S51839 – Designing the Next Generation of AI Systems:

— A quick summary, it seems any HPC networks needs to use InfiniBand… NVIDA has solution for all sizes. They can provide a POD solution!!! All Cloud providers provide their services.

  • S51112 – How to Design an AI Supercomputer for Fast Distributed Training, and its Use Cases:

— Very interesting talk from NEC Japan. They built a network based on Ethernet switches for HPC with GPUs (and not IB as seen in the other video). As well they are heavy in RDMA/ROCEv2. And seems they have dedicated ports in the network for storage, management, etc. They are very happy with Cumulus/Linux as NOS.

  • S51339 – Hit the Ground Running with Data Center Digital Twin Automation:

— Interesting tool NVIDIA air for creating labs. I expected in the demonstration to show off and built a huge network. “Digital Twin” looks like the new buzzword in the network automation world.

  • S51751 – Powering Telco Cloud Services with Open Accelerated Ethernet:

— This is from COMCAST. And it is very interesting how “big” looks like SONIC is becoming. And NVIDIA is the second contributor to SONIC after M$! I need to try SONIC at some point.

  • S51204 – Transforming Clouds to Cloud-Native Supercomputing Best Practices with Microsoft Azure:

— Obviously, building NVIDIA based supercomputers in M$ Azure. Again, all infiniband.

And another thing, the Spectrum-4 switch looks insane.

AWS Networking Videos – March 2023

I watched very interesting videos about AWS networking. They are high level, so they dont tell you the magic sauce you would like to know but it is nice that this info is out in the public.

  • DKNOG – How AWS is evolving its peering-edge in 2023 and onwards link + event:

— Evolution from buying chassis to building your own devices: consume -> create (NOC-less, auto-remediation, active telemetry, etc)-> innovate (freedom to examine trade-offs, 1U devices). Clearly use of “Clos” networks and they linux-based software.

— Delighted: low complexity + high innovation

— Simplicity Scales

— It is interesting the view of a router/brick like a set of 1U devices (rack 102.8T – 200x400G ports for customers, non-blocking). An it is very good they have pictures of the concept of “bricks” and “spines”.

— Challenges with cabling (SN connector — no patching rack needed) and 400G ZR+ (heating!)

— BGP peering is actually with a container:

— James Hamilton paper – link + pdf

  • AWS re:Invent 2022 – Dive deep on AWS networking infrastructure (NET402)– link

— summary: This is “similar” to the DKNOG but with longer and some other details like:

— “We dont like chassis”. 1+million devices

— SDR at NIC level so one TCP flow is actually load-balanced in several paths

— Hybrid SDN approach: You have controllers to give you a big picture view (I guess it provides the visibility to say “just send 70% traffic to this device” – but not sure how) and the own device device capability to deal with changes.

— Telemetry, continuous monitoring, triangulation: Be able to detect the port/device is causing the problem.

  • AWS re:Invent 2022 – Leaping ahead: The power of cloud network innovation (NET211-L) – link:

— AWS Global Infrastructure: Backbone capacity

— Customer SW/HW

— Everything fails all the time

— GPS locations in fibers! + inject light in fiber to double check fault -> intelligent optical routing/failover -> better than BGP….

— Termite sheet fibers for Australia 🙂

— Nitro card = NIC (offload card)

— SDR: not need in-order packet deliver as required by TCP. 25Gbps flows allowed now.

Dune6: Chapter House

This is the last book from the original Dune series. Thinking of the first books, looks like a different world although there are references to the beginning. The end is quite open so you can think this is can continue in more books as with the time there is always a new plot/drama. Although there are many things I dont understand. The couple of “Face Dancers” in contact with Duncan? I like the references to Van Gogh pictures like “Thatched Cottages at Cordeville“.

I would never think that Duncan would be present in all books and being a critical character.

But at the end, all is about love and the repression of it like Bene Gesserit do.

And quite moving the last words from the author about his wife death.

Bolo Podre

This is a typical Southern Portugal cake that I tried two Christmas and quite liked as looks simple and tasty. So finally this weekend was the time to try this recipe.

Ingredients:

  • 2 medium eggs
  • 100g sugar
  • 100g honey
  • 75ml olive oil
  • 150g plain flour
  • 1/2 tbs cinnamon
  • 1/2 tbs baking powder
  • 1/2 ground anise grains.
  • A bit of butter

Process:

  • Pre-heat oven at 180C
  • Whisk eggs and sugar until double in volume. It takes time doing it by hand!
  • Add honey and oil, bit a bit and keep whisking.
  • Add flour, cinnamon, baking powder and anise. Mix all well
  • Pour the mix in a greased tin.
  • Bake for 45 minutes aprox. Use a tooth stick or similar to check the inside is cook before removing from oven.

Result:

It raised more than I expected. It wasn’t as moist as I remember but it was tasty. Based on the ingredients reminded me of a olive-Greek cake I did some months ago.

I checked other recipes like this so maybe I will try again at some point.

Wafer-Scale

Somehow I came across this company that provides some crazy numbers in just one rack. Then again nearly by coincidence I show this news from an email that mentioned “cerebras” and wafer-scale, a term that I have never heard about it. So found some info in wikipedia and all looks like amazing. As well, I have learned about Gene Amdahl as he was the first one trying wafer-scale integration and his law. Didnt know he was such a figure in the computer architecture history.

Lemon Pudding Souffle

Lemon zest garnish ingredients:

  • 1/2 lemon skin cut at julienne (long and narrow stripes)
  • 50ml water
  • 50g caster sugar
  • 1/2 lemon juice

Process:

  • Mix water and sugar in a pan. Heat up to boil water.
  • Add the lemon zest and mix for 10 sec, while water is boiling
  • Add lemon juice and keep mixing for another 10 sec.
  • Check the mix is getting some consistency then remove from heat
  • Let it cool down for later. It should be like a syrup and solidify while cooling down. You can heat it up in microware for 10-15s to make it liquid again.

Lemon Pudding souffle ingredients:

  • 125ml milk
  • 35g butter
  • 70g caster sugar
  • 70g plain flour
  • 2 eggs yolks
  • 4 eggs whites
  • 1/2 tsp vanilla paste
  • 1/2 lemon zest
  • butter and sugar for greasing

Process:

  • Pre-heat oven at 180C
  • Grease (solid butter and sugar) 4 dariole moulds. Be sure there is no shiny parts! Cut a small square of baking paper and put in the bottom of the mould.
  • Make a “beurre manie” that is mixing the butter and flour by hand in a bowl.
  • Scold the milk with the vanilla (just hit the boiling point). Then at medium heat, add pieces of the “beurre manie” and whisk non stop with the milk. It is like doing “bechamel” sauce. Once the whisk is not useful, move to a wooden spoon and keep mixing.
  • At the end you will have kind off a ball, keep cooking for 1-2 minutes to be sure the flour is properly cooked.
  • Remove from heat and let it cool down
  • Add the 2 egg yolks one at each time to the “ball”. It should become like a thick cream.
  • Whisk the egg whites until snow peak. Then add the sugar and lemon zest and whisk again until snow peak. This is the meringe
  • Now fold a 1/3 of the meringe into the pudding butter. Keep doing the same 1/3 at the time.
  • Once you have all mixed, pour the butter into the moulds up to 3/4.
  • Using a deep tray, put the moulds and fill it with water (hot if possible). Be careful the moulds dont float!
  • Bake for 20-25 minutes until golden on top and risen.
  • Prepare the egg custard while waiting

Fresh egg custard sauce ingredients:

  • 75ml double cream
  • 75ml milk
  • 35g egg yolk
  • 25g caster sugar
  • 1/2 tbs vanilla paste

Process:

  • In a glass, mix egg yolks and sugar.
  • Mix double cream, milk and vanilla in a sauce pan. Add a bit of the sugar and put to the boil.
  • Add the egg mix to the liquid and mix with a wooden spoon.
  • Keep mixing until the liquid thick up a bit! Dont over do it! If you ran a finger in the back of the spoon when covered with the custard, it should keep apart.
  • Remove from heat and pour it in a container. Cover with cling film

Presentation:

  • Once the pudding moulds are ready, remove the mould, be sure you take off the paper too!
  • Put each pudding in the middle of a dish.
  • Pour the custard around the pudding
  • Put a spoon of the lemon syrup on top of the pudding (put in microware if solid)

This is it!

It was actually quite nice. Spongy and lemony.

Dundee Cake

This is a typical Scottish cake and I learned today via an e-course.

Ingredients

  • 180g softened butter
  • 90g caster sugar
  • 90g dark brown sugar
  • 115g plan flour
  • 110g self-raising flour
  • 1/2 tsp baking powder
  • 300g dry mixed fruit
  • 1 tbsp of fresh grated ginger
  • 1 orange: juice + zest
  • coconut flakes for decoration
  • 50ml Scotch whiskey (optional)
  • 1 tsp grated nutmeg
  • 1 tsp ground ginger
  • 2 tsp ground cinnamon
  • optional: whiskey butter: 75g softened butter + 75g icing sugar + 1 tbsp whiskey

Process:

  • Pre-heat oven at 150C. Grease and line a baking tin 20x30cm aprox
  • Soak the dried fruit with the whiskey, orange juice, orange zest and fresh grated ginger.
  • In a bowl, cream the butter and sugar until light and fluffy
  • Add the eggs one by one to the butter mix. Keep mixing
  • Sift the flour, spices and baking powder on the butter mix. Fold everything with a wooden spoon or spatula.
  • Drain the soaked fruit, reserve the liquid for later! Add the fruit into the dough, folding it.
  • Pour the mixture into the tin and smooth the surface.
  • Bake at 150C for 1h 20-30m aprox. Until golden and springy to touch.
  • While baking, prepare the whiskey butter. Whip the butter and icing sugar. Add the tbsp of whiskey. Whip and done.
  • Once the cake is out of the oven, immediately, brush the top with the liquid leftover (add one tsp of sugar) and then add the coconut flakes.
  • Leave it cool down

It taste a bit like a Christmas pudding but lighter. I liked it!

Calling Bullshit

This is an interesting book about the flooding of data we need to go through and the difficulty to figure out what is true or not. And I feel it many times you read something “scientific” with many numbers, stats, etc and you kind off believe that has to be true. And those new pharmaceutical drugs that are so amazing or latest paper with a dramatic breakthrough.

Interesting points:

With the hype about machine learning, understanding the algorithm may be out of our understanding but the critical thing is the training data fed into that algorithm. GIGO = Garbage In, Garbage Out. Because the training data is “biased” or not relevant, imagine how is going to be the result.

Correlation is not causation. This is a difficult topic becase we see very easily causation everywhere or find one that matches our theory.

Goodhart’s law adapted to normal people: “When a measure becomes a target, it ceases to be a good measure”. That’s so true. Think of your performance review at work, the GPU tests, etc.

Regarding the stats, it is important to pay attention to the axis: start at zero? same proportions/scales?, be mindful of 3D stats, “ducks” decorate or obscure the meaningful data,

If it is too be good to be true/false, then it isn’t.

“mathiness”: formulas and expressions that look like “good” math but they lack logical coherence and formal rigor. This is very typical for things that are not really easy to quantify (ie healthcare quality management), how things are measured?, unit? etc

One of my favourite examples is the paper about the fMRI on the brain of dead! salmons when showing picture of people showing different types of mood. This was important to clarify that MRI images maybe are not as perfect as you expect. I assume that nowadays that has improved….

Prosecutor’s fallacy: You need to prove you customer is innocent although there is DNA match in a database. There is an error rate of 1 in 10,000,000.

MatchNo Match
Guilty10
Innocent550,000,000

You are the defence prosecutor and you want to focus in the left column (blue). That means that there are 5 chances out of 6 (5+1) that your client is inocent having a DNA match.

p-values: null hypothesis and alternative hypothesis. Most papers are based on a p-value of 0.05 (now you have Goodhart’s law)

Refuting Bullshit:

  • Use “reductio ad absudum”
  • Be memorable (dead salmon example)
  • Find counterexamples (immune system theory vs trees)
  • Provide analogies (74M$ -> 2sec faster)
  • Redraw figures
  • Deploy a null model

I leave a lot of things behind that I dont remember but it is worth the reading (and more than once)

In summary, the goal is to be “smart” sceptic and dont believe everything throw to us.