CCNA DC - more quick hit notes to self

A few more notes to jog my memory:

Ethernet is 802.3 and includes wiring of some sort.  Wireless LAN is 802.11 and is not Ethernet.

The Frame Check Sequence (FCS) is 4 bytes and is in the Ethernet trailer.  It is used for error detection by computing a value and verifying it is the same when the frame is sent.

Ethernet standards:
802.3 = 10Base-T
802.3u = 100Base-T
802.3z = 1000Base-LX (max distance is 5000m)
802.3ab = 1000Base-T
802.3an = 10GBase-T

GBIC - Gigabit Interface Connector
SFP - Small Form-factor Pluggable module

Crossover cable connects pin 1 to pin 3 and pin 2 to pin 6.
Gb Crossover cable crosses pairs of wires, 1-2 go to 3-6, 4-5 go to 7-8

A data link header:
| Preamble | SFD | Src MAC | Dst MAC | Type | ---Data+padding--- | FCS     |
|   7B     |  1B |   6B    |    6B   |  2B  |        1500B       |  4B     |
| -----------------Header-------------------|  --- Payload ------| Trailer |

SFD - Start Frame Delimiter, signifies that the next sequence is the source MAC address.

A hub is a L1 device, repeats on all ports except the originating.

CCNA Data Center - opening remarks

I am about to complete my CCNA Data Center certification.  I have a CCNA Route & Switch due to expire in August, and with the change in my career focus to data center technologies, I felt it was more appropriate to continue this certification path in the data center instead of route/switch.

I'm beginning with the DCICN 640-911, "Introducing Cisco Data Center Networking" exam.  it covers many of the same topics as the CCNA R/S so I'm figuring I'll have a leg up.

So I purchased the Cisco certification guide and will begin there.

The Cisco guide begins with Networking fundamentals, including the OSI model, ethernet LANs, WAN and IPv4 addressing and routing.  It also goes into the fundamentals of TCP/IP transport and applications.

While I have to admit I don't use it every day, I do recall that the OSI model consists of:

1. Physical Layer - the actual wiring and connectors
2. Data Link Layer - physical addressing, error detection (CRC), Protocols include PPP, Frame Relay, HDLC
3. Network Layer - logical addressing network devices, IP addresses, protocols include IP, IPX, RIP
4. Transport Layer - end-to end communication and defines buffering, window size and flow control, error correction.  Protocols include UDP, TCP, SPX
5. Session Layer - Establish, maintain and tear down sessions. Protocols include SQL, RPC, NFS
6. Presentation Layer - Compression, encryption and decryption happen at L6.  Here protocols include ASCII, JPEG, GIF
7. Application Layer - makes data available to software, protocols include FTP, telnet, HTTP(S), SMTP

Where TCP/IP combines some of these into:

1. Link - OSI L1-L2
2. Internet - OSI L3
3. Transport - OSI L4
4. Application - OSI L5-L7

As data moves from one layer to the next, it encapsulates the data it receives from the previous layer, adds some info to the header and passes it to the next layer.  The terminology for the encapsulated data at each layer is:

1. L1 - bits
2. L2 - frame
3. L3 - packet
4. L4 - segment
5. L5-L7 data

Instead of bits-frames-packets-segments-data, the OSI model uses "Protocol Data Units" such as L7PDU, L6PDU, which consist of the data encapsulated in that particular layer's header and trailer.  Someone should have thought of that before everyone started with the commonly used terminology above...while it's more clear, let's face it...nobody uses that.

And a few other reminders for myself from chapter 1:

Adjacent-layer communication happens within the same computer between different layers, while same-layer communication occurs between different computers.  Adjacent-layer communication is when one layer requests or provides services to the layer above or below it.

The TCP/IP model in recent years shows the Link Layer at level 1 split into 2 layers, the Data Link and Physical layers.

Sending an F11 to ESXi from a Macbook Pro when using RDP to a Windows system for installation

Many more irritating moments spent wishing I had written this down somewhere.

I work remotely much of the time.  I'm currently reinstalling ESXi on a number of hosts and using a workstation located on the LAN of my office to hold the install ISO.  I'm accessing it via RDP from a Mac connected by VPN.  I have configured my Mac to use F-keys in a more traditional manner like I recorded in this post, but for some reason the F11 would show the desktop instead of actually instructing the ESXi installation to continue.

The secret key sequence is:

Command+F11

I don't know what it is about the Mac that makes it behave like this, but I'm tired of wasting time searching for this answer.  I hope I remember it now...