Sails.js is a MVC Framework for Node.js
Create a new sails project
sails new {your-app-name}
Create a new Controller(apis)
sails generate api {generator-name}
Virmach 2020 Black Friday review
VirMach, A ColoCrossing reseller. Good? Not bad. Cheap? Yes!
SmallWooden 6.2USD/Annually
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DryKey 4.5USD/Annually
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VirMach use Track - How to enable AES-NI without opening a ticket
You may already find that two box above, one is AES-NI enabled but another one not.
When you reinstall your OS in VirMach’s SolusVM:
You can see some operating system is end with a gen2
If you install these gen2 template, your box will likely to enable the AES-NI. Even you reinstall to other OS later, the AES are still enabled.
Personlly, I install Debian 8 x 86_64 Minimal v1 (gen 2)
How to host a Hexo Blog on your Windows laptop with server
Since I recently learned about Nodejs, and I will probably focus on nodejs in the foreseeable future, I migrated my blog from Wordpress to Hexo.
Here is a little note about how to install a hexo blog.
Install VSCode
This part you need to do it yourself.
Install scoop
Scoop is a package manager on Windows. Highly suggested.
Type the following into PowerShell to ensure that local scripts are allowed to execute.
set-executionpolicy remotesigned -scope currentuser
Then install Scoop by executing the following command.
iex (new-object net.webclient).downloadstring('https://get.scoop.sh')
Just wait for the script to finish, and once it’s installed successfully, let’s try the following
scoop help
Finally install nodejs with scoop.
scoop install nodejs
Install hexo and git
Use npm to install hexo on your laptop:
npm install -g hexo-cli
Open the folder you want to store your blog data, then create a blog by using the following command:
hexo init [folder] // [folder] = your blog’s path
Open the project folder with VSCode:
npm install
Finally,
hexo s
Open your browser and localhost:4000 to see your website
Create a github repo
Follow the command provided by github:
Push your blog to Github
Every git-push process need the following three commands:
1 | git add . |
You can open terminal on VSCode by clicking Ctrl+`
Host on Netlify for free
Well, I am lazy… and Netlify already did the job
To be continues…
Networking Notes 6 - Network Performance Measures
Network Performance Measures
- Throughput
- How much data travels across the network
- Average packet delay
- How long does it take for a packet to arrive at its destination
- How responsive is the system to user commands
- Can the network support real-delivery such as audio and video
Routing Algorithm
“Good” path:
- The minimum cost path
- Other definitions are possible
Hop count
The number of routers a packet must go through
Least-cost routing
Associate a cost with each link
- Bandwidth
- Delay
- Reliability
To make routing decision:
Topology of the network
Traffic load
Link cost
Information should always keep up-to-date
More information
Fixed Routing
Central Directory is usually stored at a network control center
Matrix table
No different between Datagram and VC
Advantages
- Simplicity
- Work Well in a reliable network with a stable load
(IPLC?)
Disadvantages
- Lack of flexibility
- Do not react to network congestion or failures
Flooding Algorithm
Packet sent to every neighbor node
No network information required
Evenually a number of copies will arrive at destination
Guarantees the packet reaches the destination in the shortest time
Duplicate packets are generated.
Node can remember packets already forwarded
Advantage
- Very rebust
- Used for sending emergency messages
Disadvantage
- High traffic load
Random Algorithm
The outgoing link is chosen at random
Round-robin?
- Advantages
- Robust and simple
- no network information
- Less traffic load compare to flooding
- Disadvantages
- Longer path
- Performance not guaranteed
Adaptive Routing
Used by almost all packet switching network
** routing decision changes as network conditions change**
Failure Link
Network congestion
Require network information
Network information must be exchanged among the nodes
Decisions are more complex
Advantages
- Impoved performance
- Congestion control
Disadvantages
- Substantial processing burden on nodes
- Increased network traffic traffic due to the exchange of network information
- Reacting too quickly can cause oscillation
Distance Vector Routing
Each node communicates only with directly-attached neighborsA routing table is created by building up a common set of routers in close proximity to each other, hence the term “distributed”.
Each router on the network must maintain a two-dimensional Vector Table, which records the best known distance from its own router to each router.
A router periodically builds a routing table by exchanging vector tables with neighboring routers (not broadcast to all routers).
When a router receives a vector table from its neighbors and then corrects its own vector table, the contents of the vector table are continually corrected and retransmitted, and the entire network state is gradually passed to each router.
As the routing tables on the routers become more complete, it becomes possible to find the best path. The vector table is sent only to the neighboring routers, which consumes less bandwidth and does not cause broadcast oscillation.
Link State Routing
Information sharing - each router shares its knowledge of its neighbourhood with all routers in the network.
After all LASs from all nodes are gathered, the entire map of the network can be constructed.
Least-Cost Algorithms
- Dijkstra’s Algorithm
- Bellman - Ford Algorithm
We Will come back for the Algorithm later
Networking Notes 5 - Switching
Pactket-Switched Networks: Routing
Two Main approaches to implement packet switching
- Datagram approach
- Virtual circuit approach
Datagram Network
- connection-less network
- destination address determines next hop
- routes may changee during session
Datagram Approach
- Connectionless switching
- Each packet(datagram) is treateed indeependently
- Packets may go by different paths across the network
- May arrive out of order, the transport layer neeeds to reorder them
Virtual circuit network
- Connection-oriented switching
- Call request and call accept packets are used to establish the connection between sender and receiver
- Each packet carries tag(virtual circuit ID), tag determines next hop
- fixed path determined at call setup time, remains fixed thru call
- routers maintain per-call state
- Path is fixed
Virtual Circuit approach
- All packets of the same message are transferred via a preplanned route(same route)
- Arrive in order
- Eatablish between sender and receiver at the beginning
There are two main virtual circuit
Permanent virtual circuit(PVC)
- Set up by the network provider
- No need to terminate the VC after transmission, and no need to set up the VC before it(because it is already seted up by network provider)
Switch virtual circuit
- Setup everytime when a VC is needed, and terminate after the transmission
- May get different VC according to network conditions
- More flexible, but required extra set up time before data transfer begins
- Connection establishment
- Data transfer
- Connection release
VC vs Datagram
VC
- sequencing and error control
- No routing decisions to make -> Packets are forwarded more quickly
- Less reliable
Datagram
- No call setup phase - Good for bursty data
- More flexible
- can have alternate route
- can avoid congested parts of the network
Switching
Switching in computer network helps in deciding the best route for data transmission if there are multiple paths in a larger network
One-to-One connection
Packet Switching
- The internet is a packet switched network
- Message is broken into individual (Packets)
- Each packet is sent individually
- Each packet will have source and destination IP address with sequence number.
- sequence number will help receiver
- Reorder the packets
- Detect missing packets
- Send acknowledgments
Networking Notes 4 - Network support group
Network Layer
Network layer is concerned with getting packets from source all the way to destinations.
It is the lowest layer that deals with end-to-end transmission, and may make many hops at intermediate nodes.
Physical and data link layers only operate locally.
Hop - is one portion of the path between source and destination.
Network-Layer Function
- Connect heterogeneous networks together to look like a single network (Internetworking)
- Uniquely identify each device (addressing)
- Make decision to deliver data (routing)
- Fit data to size used by the lower layer protocol (fragmentation)
Jobs for sending side: encapsulates segments into datagrams
Jobs for receiving side: delivers segments to transport layer
Address in TCP
Physical address
Logical address
Port address
Physical Address
Address of a node as defined by its LAN or WAN
In a data link level, frame transfer only contains Physical addresses in the header.
Most LAN use a 48-bit(6bytes) physical address written as 12 hexadecimal digits with every digits separated by a colon.
Physical Address also called Media Access Control (MAC) address
MAC address is performed via the Address Resolution Protocol (ARP)
Logical Address
Universal address that can pass through the LAN boundaries.
Address of a LAN. Logical Address + Physical Address needed to send data to another LAN network.
Port Address
Computer can run multiple processes at the same time, but need to label different processes by using port address
Port address is 16-bit address. (2^16) 0 - 65535, 65536 in total.
DNS
Domain Name System
Translation of a hostname into an IP address.
Networking Notes 3 - Internet Transport-Layer Protocol
More than one transport-later protocol available to applications
Internet: TCP and UDP
TCP
- Reliable, in-order delivery
- Connection setup
- Flow control
- Congestion control
UDP
- Unreliable, unordered delivery
More about TCP
Full name: Transmission Control Protocol
- Connection-oriented protocol
- Provide a reliable unicast end-to-end byte stream over an unreliable internetwork
Before any data transfer, TCP establishes a connection(hand shark?)
- Client: send Request a connection
- Server: Accept a connection
- Do Data Transfer
- Client: Disconnect
Reliable
- The reason why we use TCP is because it is reliable.
- Byte stream is broken up into chunks - segments
- The receiver sends acknowledgements (ACKs) for segments.
- TCP maintains a timer, if ACK is not received in time, the segment is retransmitted.
- Detecting errors (checksums for header and data)
- Each byte has a sequence number
UDP
Full name : User Datagram Protocol
- Connectionless - no handshark
- Unreliable
- No flow control
- No congestion control
Good:
- No connect establishment ← can add delay
- simple
- small segment header
- no congestion control: as fast as desired
Good for: Streaming multimedia application
- Loss tolerant
- rate sensitive
- DNS
Networking Notes 2 - Addressing
Network Notes 2
IPv4
Each IPv4 have 4 byte, 5 classes
Class - 2-level hierarchy of IP address(Netid+Hostid)
- A: Byte1 Netid; Byte2,3,4 Hostid
- B: Byte1,2 Netid; Byte 3,4 Hostid
- C: Byte1,2,3 Netid; Byte 4 Hostid
- D: The address range of IP Multicast, is 224.0.0.0 ~ 239.255.255.255.
- E: The address range of ?,240.0.0.0~255.255.255.255
I should only focus on ABC here.
The 2-level hierarchy of IP addresses is not sufficient for organizations
Subnetting
We usually want to division of a network into smaller networks(subnet).
We have 3 level of IDs of hierarchy
- NetID
- SubnetID
- HostID
In a subnet, Device can phtsically reach each other without intervening router.
Masking
Masking is the process of extracting the network address from an IP address
- Default Mask: used by routers outside
- Subnet MaskL used by route inside
Mask
- 32 bits long
- NetID = 1
- HostID = 0
IP address Essentially a binary number
Example:11111111 00000000 00000000 00000000 = 255.0.0.0
Masking is AND operation of the IP address
The 11111111 is the netID and the 0s is HostID.
NetIDs are managed by Regional Internet Registries
- APNIC (Asia)
- ARIN (American)
- LACNIC (Latin American)
- RIPE NCC (Europe)
HostIDs are managed by the network administrator(owner of the NetID)
CIDR - Classless InterDomain Routing
The length of the network prefix in IP addresses is kept arbitrary.