Network Security and Threats (and search engine indexing probably)

what is a firewall?

• A security checkpoint designed to prevent unauthorised access between two networks 

• The networks could be an internal, trusted network and an external, untrusted network like the internet 

• can be hardware or software, can also be in routers 

• Monitors incoming and outgoing network traffic 

• Usually consists of a computer containing two NICS (one for internal one for external) 

• Each data packet passing betweeen the NICS is analysed, then accepted/rejected 

what is static packet filtering?

• Controls network access according to network administrator rules and policies 

• Examines source and destination IP addresses in packet headers 

• if IP addresses are on allowed list, they are accepted 

• Packets can be blocked based on their protocols or port numbers 

• Port= when a packet reaches the network and is directed to a particular area to download its payload data to the computer 

• a dropped packet is quietly removed, whereas a rejected packet causes a rejection notice to be sent back to the sender 

what is stateful inspection (dynamic filtering)

• Checks the payload (data) of the packet instead of just the header 

• Continuously monitors incoming and outgoing traffic after a connection is established 

• Even if the data packet has a non-suspicious protocol (TCP) it could still be stealing data or installing malware 

• That sort of attack wouldn't get caught by static filtering because static filtering only checks the header and not the data 

• Maintains a connection table or state table, keeping track of all the conversations happening between trusted and untrusted networks 

• Ensures all inbound and outbound packets are expected as they all match whats in the table 

what are proxy servers?

• Intercepts all packets entering and leaving a network 

• hides true IP addresses, enabling privacy and anonymous surfing 

• Can maintain a cache of commonly used websites and return their data to user immediately without having to reconnect to internet and re-request page 

• Therefore speeds up access to webpages and reduces web traffic 

• If webpage not in cache, proxy will request it using its own IP address, return data to user, then add page to its cache for others in the same server 

• Can log all user activities for monitoring/safeguarding purposes 

• School networks use them to filter websites 

• Can serve thousands of users 

• By using proxy server based in different geographical location, users can watch videos on streaming sites that are permitted in that location but not with their home IP 

what is the search engine index?

• a record of all the resources/webpages located on the world wide web

• each entry in the index contains information like url, content of webpage, quality, keywords etc

• when a user searches the world wide web they are actually searching the index

• provides accurate and fast information retrieval for search engine users

what are web crawlers?

• internet bots

• they visit each website in the index, then follow all the hyperlinks on those pages, then follow hyperlinks on those pages to get to billions of webpages

• for each website they visit they update the index with information about the webpage

what are metatags?

describe the content of a web page

include keywords relating to the content of the webpage

if words from the user’s search query appear in the metatags, the website is more likely to be shown to the user

what is the pagerank algorithm?

• PR\left(A\right)=\left(1-d\right)+d\left(\frac{PR\left(T_1\right)}{C\left(T_1\right)}+\ldots\ldots+\frac{PR\left(T_{n}\right)}{C\left(T_{n}\right)}\right)

• PR= pagerank

• A= page A (the page currently getting pageranked)

• the T pages= pages that have outbound links from those pages to A

• C = the number of outbound links coming from each T page

• d= the damping factor, 0.85, which represents the probability of a web user reaching that webpage by clicking on links until they get to it

• constantly recalculated and updated

• pages with lots of other pages linking to that page have higher pageranks

what factors affect the pagerank of a page?

• domain name

• number of inbound links

• frequency of search term

• age

• frequency of updates

• magnitude of updates

• keywords in h1 tags