Need some advice on learning networking

[slimslob]

Re: Need some advice on learning networking

I haven't covered BGP and I'm not sure if it's covered in the CCNA course. I briefly looked it up just now and the protocol is the only one that will route over the internet for huge networks. Without knowing how it works, it's impossible (for me) to understand what went wrong.

The way I read the Malwarebytes lab article Facebook in effect told the rest of the internet that they no longer existed.

[BillyCarpenter]

Re: Need some advice on learning networking

I can now look at a diagram of multiple inter-connected switches and tell you which switch will be elected the root bridge and further tell you what port on that switch will be elected the root port. Also, I can tell you which ports will be blocked by spanning tree. It took a hell of a lot of studying and practice to be able to do that. Fortunately, Spanning Tree Protocol has a set of finite rules...so that helps.

[BillyCarpenter]

Re: Need some advice on learning networking

The way I read the Malwarebytes lab article Facebook in effect told the rest of the internet that they no longer existed.

I did a little more research on the BGP protocol. It's not unlike a lot of other routing protocols in that it is responsible for connectivity of many routes to their logical destination. And the routing table is automatically updated any time a change is made or a route goes up or down. With that being said, there are so many things that a network engineer could do to bring the system down. It had to be something catastrophic because these networks are designed to have multiple routes to the same destination.

[BillyCarpenter]

Re: Need some advice on learning networking

slim got me curious as to what happened with Facebook and here's what I found:

Facebook went down because the "faulty configuration change" meant that it stopped telling routers where its data centres were, it appeared to the routers that they simply didn't exist.


How bad is that?


Normally it would be quite straightforward to fix this kind of outage - you start advertising where your servers are and routers begin connecting to you again.


Unfortunately, it seems that Facebook was using the same network for staff to access the network remotely, meaning that the outage prevented them fixing the outage.


The only solution was to physically go to the data centres and refresh things from there - but there was a problem with this too, according to a now-deleted post on Reddit believed to have been posted by a Facebook staff member.


The access cards that Facebook use to physically enter its premises were also dependent on the internal systems working properly. The outage meant that they couldn't authenticate to the premises and get inside.

A "faulty configuration" means that the IT staff was manually configuring the routers. I spend every day configuring routers and switches as part of my CCNA course and you've heard me say that one tiny mistake can bring down an entire network.

They mentioned that the routers "didn't know they existed." That's interesting. The command line "neighbor ip-address shutdown" would make the routers think they didn't exist and if that command line were executed, remote access would no longer be possible and they would have to physically access the routers. That's just one example of what could have happnened.

[rthonpm]

Re: Need some advice on learning networking

A "faulty configuration" means that the IT staff was manually configuring the routers. I spend every day configuring routers and switches as part of my CCNA course and you've heard me say that one tiny mistake can bring down an entire network.

They mentioned that the routers "didn't know they existed." That's interesting. The command line "neighbor ip-address shutdown" would make the routers think they didn't exist and if that command line were executed, remote access would no longer be possible and they would have to physically access the routers. That's just one example of what could have happnened.

Facebook uses a very specialised infrastructure, and even builds its own internal routers. They are also at a size where they have a direct tie to the real big iron of the Internet to which usually only Tier 1 ISP's have access. Since they also manage their own DNS servers for their various properties, when they knocked everything offline between their data centres it took those down and with that direct pipe in place, that change was replicated to the core Internet in close to real time.

There are some really good technical descriptions of what happened online once you dig past the superficial ones from the general news sits and go to the more technical sites.

Also: BGP wouldn't likely be covered in CCNA as it's more or less an ISP level protocol as opposed to internal networking. Big iron routers do much the same tasks as their more common cousins, but the working of them is a little more detailed.

Sent from my BlackBerry using Tapatalk

[BillyCarpenter]

Re: Need some advice on learning networking

Facebook uses a very specialised infrastructure, and even builds its own internal routers. They are also at a size where they have a direct tie to the real big iron of the Internet to which usually only Tier 1 ISP's have access. Since they also manage their own DNS servers for their various properties, when they knocked everything offline between their data centres it took those down and with that direct pipe in place, that change was replicated to the core Internet in close to real time.

There are some really good technical descriptions of what happened online once you dig past the superficial ones from the general news sits and go to the more technical sites.

Also: BGP wouldn't likely be covered in CCNA as it's more or less an ISP level protocol as opposed to internal networking. Big iron routers do much the same tasks as their more common cousins, but the working of them is a little more detailed.

Sent from my BlackBerry using Tapatalk

There's no doubt that BGP is beyond the scope of CCNA. And you're correct that Facebook builds some of their own routers. I actually posted an article a few months back that discusses Facebook engineers using a server as a router. They were unhappy with routers from other companies because they weren't built for what they needed to do.....so they made their own. All a router is is a dedicated computer.


Thanks for sharing. It's interesting to discuss even if I don't fully understand.

[BillyCarpenter]

Re: Need some advice on learning networking

I took a pretest today and one of the questions kinda took me by surprise because it involved network fundamentals but I don't remember covering this.


Here's the question:


What interface counter is most often associated with duplex mismatches?



I hadn't the foggiest clue as to what counter they were referring to. All I knew is that a speed mismatch on the interface from one switch to another would cause performance issues...slow speeds and/or dropped packets.


Here's the answer and I'm gonna be checking this out because it will come in handy for troubleshooting purposes.



Answer: Late Collisions

Explanation

The misconfiguration of duplex setting between switches cause collisions on a switch port. The late collisions interfaces counter increase as a result. Note that duplex mismatch has no effect on the operational state of interfaces (up/up). Packets are still forwarded however performance is often affected.


The output of show interfaces display interface errors such as runts, giants, collisions and CRC. The most common cause of CRC and runts is collisions. Gigabit Ethernet switch ports have eliminated collisions unless there is a configuration error or defective hardware. Collisions can occur when network interface hardware or cabling is defective as well. Giant frames (1600 bytes) result either from faulty interface hardware or MTU misconfiguration on an interface.


The high number of input errors and CRC errors indicate a Layer 1 issue between switches. The local switch is sending frames that are corrupt when they arrive at the neighbor switch. The most probable cause is duplex mismatch between the switch interfaces or cabling errors. The switch ports must agree on duplex setting. Gigabit Ethernet ports do not support half-duplex at all. The older 10/100/1000 interfaces permitted half-duplex with lower speed settings.

[BillyCarpenter]

Re: Need some advice on learning networking

There's no doubt that BGP is beyond the scope of CCNA. And you're correct that Facebook builds some of their own routers. I actually posted an article a few months back that discusses Facebook engineers using a server as a router. They were unhappy with routers from other companies because they weren't built for what they needed to do.....so they made their own. All a router is is a dedicated computer.


Thanks for sharing. It's interesting to discuss even if I don't fully understand.

I did a little more research on BGP. First, BGP isn't taught at the CCNA level. You first learn about BGP at the CCNP level.

Secondly, BGP is a routing protocol that is used by the Internet Service Providers. One ISP advertises routes to the other ISP's thru BGP. In other words it's strictly an internet routing protocol.

[BillyCarpenter]

Re: Need some advice on learning networking

As of late, I've focused more of my attention on passing the CCNA exam. Over 90% fail the exam on the first attempt. I do not intend to be part of that statistic.


Earlier I took a practice exam and I've been going over the questions that I missed and I must say that, as a result, I have learned some things that I didn't know.

For starters, there are counters and other information that reside in the switch that reveal if there's a bad/faulty cable on a specific port or if there's a duplex/speed mismatch between switches. This will come in handy.


Likewise, I went back and dug deeper into how a route makes into the routing table and what routing protocols are preferred over other ones. Better known as Administrative Distance. I knew most of it already but I did pick up a few things. All part of the process. As long as I know more when I go to bed than I did when I woke up...I consider that to be progress.

[BillyCarpenter]

Re: Need some advice on learning networking

Any of you ever heard of frame switching?

Apparently this was in vogue in the 1990's. It's well on it's way out today but I understand that it's still in use by some companies.

Trust me, I'm not digging up old technology because I find it exciting. Nope. There was a question about frame switching on my practice test and I had no idea what they were talking about.

From the research that I've done, here's how it works...in general terms.

If we have an office in New York and Boston and we want connectivity, we have a few options. One is a dedicated leased line. But that's very expensive and not really scalable. if you have 4 or more offices.

This is where frame switching comes in at.

Basically, the ISP has a "frame relay switch" and it's shared by many different customers. The office in Boston and New York can plug into the frame relay switch and after it does its magic, we have connectivity. And if our company grows, they can plug into the frame relay switch and we'll have full mesh connectivity. And because it's shared by many, so is the cost.


That's a very general description.

I have to learn this because the OSPF routing protocol behaves very differently when configured on a frame relay circuit. It's complicated stuff and there's not much information on it because of it's age.

[BillyCarpenter]

Re: Need some advice on learning networking

You can officially have me locked up in the loony bin. This frame relay circuit has blown my mind totally.


We've all heard of "arp", right?

Well, have you ever heard of "inverse arp" ?

What about a "dlce" ?

Oh my!!!!!!!!!!!!!!!!!

[BillyCarpenter]

Re: Need some advice on learning networking

Frame Switching is a technology from the 1990's and that's where they should have left it. To understand networking, we must learn to dissect protocols. Having a thorough understanding of protocols is the key to troubleshooting a problem. And Frame Switching is no different. I had to learn the protocol before I could understand it. The only difference is that this protocol was more complex than any other that I've covered. It took a long time to learn and I'm still foggy in a couple of areas.

I want to drive the point home about protocols. Let's apply this to the copier world. Take SMB for example. Do we understand this protocol? Can we effectively troubleshoot a SMB problem without understanding it? I once looked at SMB on Wireshark and I was able to get the total picture of how it works. Well, it's no different in a production network. The only difference is that we're dealing with MANY more protocols and each one must be learned if we're gonna pass the CCNA exam.

I think when I'm done with CCNA that I'm gonna get certified on WireShark. That seems like the logical next step in my journey.

[rthonpm]

Re: Need some advice on learning networking

You may say that some protocols should have stayed back in the 90's, but you would be HORRIFIED at what you'll find in many networks. There are still piles of dead and ancient protocols and methods still in use whether through inertia or a lack of knowledge of just what is on the network so ancient settings and protocols get kept 'just so nothing breaks'.

Sent from my BlackBerry using Tapatalk

[BillyCarpenter]

Re: Need some advice on learning networking

You may say that some protocols should have stayed back in the 90's, but you would be HORRIFIED at what you'll find in many networks. There are still piles of dead and ancient protocols and methods still in use whether through inertia or a lack of knowledge of just what is on the network so ancient settings and protocols get kept 'just so nothing breaks'.

Sent from my BlackBerry using Tapatalk

First of all, I feel for you having to work on that crap. But you bring up something that I haven't given much thought to. I bet there are a lot of companies out there that hang on to their old technology because they don't wan to pay to upgrade and, in my experience, a lot of people just don't like change and they'll limp along for as long as possible.

[slimslob]

Re: Need some advice on learning networking

First of all, I feel for you having to work on that crap. But you bring up something that I haven't given much thought to. I bet there are a lot of companies out there that hang on to their old technology because they don't wan to pay to upgrade and, in my experience, a lot of people just don't like change and they'll limp along for as long as possible.

Just remember that the Command Prompt which is still need to run some trouble shooting is a hold over from DOS.