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18 Cards in this Set

  • Front
  • Back
DNS - Domain Name System - what is it?
- It is a hierarchical naming system for computers, services, or any resources on a network.
- The Domain Name System also defines the technical underpinnings of the functionality of this database service. For this purpose it defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite (TCP/IP).
- It also stores other types of information, such as the list of mail servers that accept email for a given Internet domain. By providing a worldwide, distributed keyword-based redirection service, DNS is an essential component of the functionality of the Internet.
- (Other identifiers such as RFID tags, UPC codes, International characters in email addresses and host names, and a variety of other identifiers could all potentially utilize DNS.)
DNS - Domain Name System - 2 main functions?
- it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, www.example.com translates to 192.0.32.10
- (1) makes it possible to assign domain names to groups of Internet users in a meaningful way, independent of each user's physical location. This means Internet contact info can remain consistent and constant even if the current Internet routing arrangements change or the participant uses a mobile device.
- (2) - it distributes the responsibility of assigning domain names and mapping those names to IP addresses (by designating authoritative name servers for each domain, which in turn do same for sub-domains). DNS is distributed and fault tolerant and has helped avoid the need for a single central register to be continually consulted and updated.
What is tagging used for in switches?
- assigning one or more VLANs to switchports
Trunking
- In computer networking, trunking is a slang term referring to the use of multiple network cables or ports in parallel to increase the link speed beyond the limits of any one single cable or port. This is called link aggregation. These aggregated links may be used to interconnect switches.
- 802.1Q is an open standard, so it’s the only option in an environment with multiple-vendor equipment
- Cisco also has a proprietary trunking protocol called Inter-Switch Link
Subnet masks
- go with IP addresses
- examples
# IPs # netbits subnet mask last octet values
256 24 255.255.255.0 0
128 25 255.255.255.128 0, 128
Internet Protocol Suite
A-T-I-L
Application Layer
Transport Layer Internet Layer
Link Layer
DEFAULT
- DEFAULT is a default route that is sent to you by an ISP
- It is a way to cover all routes that they don't send to you, but offer you a way out to those routes. That means they don't have to send you the entire Internet routing table...which is ~280,000 routes now and many weaker routers will fall over and die if they get that many
AS as relates to BGP
- AS = autonomous system = is unique per company / entity
- Google is AS15169, YouTube is AS36561, etc.
- you see those numbers in the AS path in a bgp routing table and you can tell where those routes come from/through to get to you
Internet Protocol Suite - Application Layer
BGP • DHCP • DNS • FTP • GTP • HTTP • IMAP • IRC • NTP • POP • RIP • RPC • RTP • RTSP • SIP • SMTP • SNMP • SSH • Telnet • TLS/SSL
(BGP = Border Gateway Protocol)
(DHCP = Dynamic Host Configuration Protocol)
(SNMP = Simple Network Management Protocol = a UDP-based network protocol)
Internet Protocol Suite - Internet Layer
IP (IPv4, IPv6) • ICMP • ICMPv6 • IGMP • IPsec
(IGP = Interior Gateway Protocol)
(IP = Internet Protocol)
(e.g. 208.77.188.166 (IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6))
Internet Protocol Suite - Link Layer
ARP/InARP • NDP • Tunnels (L2TP) • PPP • Media Access Control (Ethernet, DSL, ISDN, FDDI)
IPv6 has a vastly larger address space than IPv4
- IPv6 uses 128-bit address (represented in hexadecimal), whereas IPv4 uses only 32 bits
- provides flexibility in allocating addresses and routing traffic and eliminates the primary need for network address translation (NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion
Interior gateway protocol (IGP)
- IGP is a routing protocol that is used to exchange routing information within an autonomous system (AS).
- In contrast, an Exterior Gateway Protocol (EGP) is for determining network reachability between autonomous systems and makes use of IGPs to resolve routes within an AS.
- 2 categories:
1) Distance-vector routing protocol: each router does not know about the full network topology. It advertises its distances to other routers and receives similar advertisements from other routers. Using this info each router populates its routing table. This process continues until the routing tables of each router converge to stable values (sometimes slow to converge). E.g. Routing Information Protocol (RIP) & Interior Gateway Routing Protocol (IGRP)
2) Link-state routing protocol: each node possesses information about the complete network topology. Each node then independently calculates the best next hop from it for every possible destination in the network. The collection of best next hops forms the routing table for the node. E.g. Open Shortest Path First (OSPF)
Proxy server
- a computer system or router that breaks the connection between sender and receiver.
- Functioning as a relay between client and server, proxy servers help prevent an attacker from invading a private network (one of several tools used to build a firewall).
- Proxy means "to act on behalf of another," and a proxy server acts on behalf of the user. All requests from clients to the Internet go to the proxy server first.
- Address Translation and Caching: proxy server is a dual-homed host with 2 network interfaces and 2 IP addresses. Proxies are often used along with network address translation (NAT), which hides all the IP addresses of the client machines on the internal network.
- Proxy servers may also cache Web pages, so that the next request can be obtained much faster.
Proxy cache
- Improves performance by transparently storing data such that future requests for it can be served faster
- When proxy servers are used, the users' browsers must be configured to use the proxy server
- As opposed to a buffer, which is managed explicitly by a client, a cache stores data transparently: This means that a client who is requesting data from a system is not aware that the cache exists, which is the origin of the name cache (from French "cacher", to conceal)
- Since the content of Web pages can change, the caching software is always checking for newer versions of the page and downloading them
- Pages will be deleted from the cache after a set amount of non-activity
Web caching types and search engine caching
- 3 kind of web caches:
1) Client Caching (e.g. CPU / hard drive / browser)
2) Proxy Caches
3) Gateway caches - Gateways translate from one Internet protocol to another (e.g. AppleTalk to TCP/IP)

- Search engines also frequently make web pages they have indexed available from their cache. For example, Google provides a "Cached" link next to each search result. This can prove useful when web pages from a web server are temporarily or permanently inaccessible.
Cached Pages - how Google uses them
- Google takes a snapshot of each page it examines and caches (stores) that version as a back-up. The cached version is what Google uses to judge if a page is a good match for your query.
- Most search results includes a Cached link, which is the Google cached version of that web page. This is useful if the original page is unavailable. Sometimes you can access the cached version from a site that otherwise require registration or a subscription.
- Since Google’s servers are typically faster than many web servers, you can often access a page’s cached version faster than the page itself.
- Google indexes a page (adds it to its index and caches it) frequently if the page is popular (has a high PageRank) and if the page is updated regularly. The new cached version replaces any previous cached versions of the page.
OC-3 and SONET
OC-3: Optical carrier, where the 3 means 3 times the base rate of 51.84 Mbps or 155 Mbps.

OC-n are physical protocols defined for SONET optical signal transmissions.

STS (Synchronous Transport Signal) frames are sent over MM fiber at n times the base rate. This is cell based transmission not Ethernet.

SONET: Synchronous Optical Networking - standardized multiplexing protocol that transfers multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs).