---
title: 'Lecture 04 Network Hardware in Depth'
disqus: hackmd
---

:::info
ST1010 Network Fundamentals
:::

Lecture 04 Network Hardware in Depth
===

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## Table of Contents

[TOC]

Network Switches in Depth
---
- work at datalink layer 2
- receive frames on 1 port & forward to port whr dest device found
- switches send broadcast frames out all ports
- ea switch port considered a collision domain
- dont forward collision info to other ports
- can operate in full-duplex
- allows connected devices to transmit & receive simultaneously - eliminates possibility of collision

### Port Modes of Operation
- ports on typical 10/100 mbps switch can usually operate in these modes
- 10mbps half duplex
- 100mbps half duplex
- 10 mbps full duplex
- 100mbps full duplex
- most inexpensive switches run in auto-nego mode
- switch sets mode to highest perf setting the device supports
- __auto-MDIX__ mode - switch port detects type of device & cable it's connected to
- straight-through or crossover cable can be used

### Creating Switch Table
- switching table holds MAC address/port pairs that tell switch whr to forward a frame based on dest MAC
- when switch powered on, its table is empty
- as network devices send frames, switch reads ea frame's src address & adds to table with port its received from
- if frame's dest not found in table, the switch forwards the frame to all ports


- most swithes include a num that indicates num of MAC addresses the switch can hold
- Eg. 8k MAC supported
- switching tables prevent stale entries by including timestamp when entry created
- when switch gets frame from device alrdy in table, it updates the entry with new timestamp
- period of time a table keeps a MAC is called __aging time__
- if timestamp not updated within aging time, the entry expires & removed from table

### Frame Forwarding Methods
- cut-through switching - switch reads only enoguh of incoming frame to determine frame's src & dest
- fastest
- disadvantage - no error checking
- store-and-forward switching - switch reads entire frame into buffers before forwarding
- examines the FCS field to enure it contains no errors before forwarding
- a frame check sequence (FCS) refers to an error-detecting code added to a frame in a communications protocol
- fragment-free switching - switch reads enough of frame to guarantee that its at least the min size for network type


### Multilayer Switches
- have funcs of switch (layer 2) but add layers 3 capabilities
- typically used in interior of networks to route between vlans instead of being placed on network perimeter
- perf advantage over traditional routers
- packet routing between vlans done within switch than having to exit switch to router


Advanced Switch Features
---
- high-end switches (AKA smart switches/manages switches) can help make network more efficient & reliable
- common features in smart switches
- multicast processing
- spanning tree protocol
- virtual lan
- port security

### Multicast Processing
- switches process multicast frames in 1 of 2 ways
- as broadcast & send to all port
- used by low-end switches or those not configured for it
- by forwarding frames only to ports with the registered multicast addr
- used by switches that support internet grp management protocol (IGMP)
- multicast MAC addr always begin with `01:00:5E`
- rest of addr identifies particular multicast app

### Spanning Tree Protocol (STP)
- enables switches to detect when there's potential for switching loop
- occurs when frame is forwarded from 1 switch to another in infinite loop
- when possible loop detected,
- 1 of switch ports goes into blking mode
- prevents it from forwarding frames that creates loops
- if loop config broken, switch that was in blking mode resumes forwarding frames


#### Side Effects of STP
- device takes longer to create link with switch that runs the protocol

#### Rapid Spanning Tree Protocol (RSTP)
- enhancement to STP that provides faster convergence when topology changes

### Virtual Local Area Networks (VLANs)
- enable you to config 1 or more switch ports into separate broadcast domains
- like separating switch into 2 or more switches that aint connected
- router needed to comm between VLANs
- improves management & security of network & gives more control of broadcast frames
- allows admins to grp users & resources logically instead of by phy location


#### VLAN Trunks
- __trunk port__ - switch port configed to carry traffic from all VLANs to another switch/router
- switch/router port must also be configed as trunk port
- involves switch adding tag to ea frame that must traverse the trunk port
- VLAN tag identifies which vlan traffic originated from

#### Consideration Factors
- overuse of vlans will cost more than it benefits you
- more vlan = more logical networks
- network more complicated
- every vlan you create needs corr router interface
- routers are slow so perf decrease with more vlan
- more router interfaces mean more IP networks
- need subnetting your existing network

### Switch Port Security
- network jacks with connections to switches often avail to public users - can plug in laptop with viruses, hacker tools or malware
- switch with port security can help prevent these types of conn
- enables admin to limit how many & which MAC can connect to a port
- if unauth comp attempts to connect, port can be disabled & msg sent to admin to alert them of intrusion

Routers in Depth
---
- operate at network layer 3 & work with packets
- connect separate logical networks to form internetwork
- broadcast frames not forwarded to other outer ports/networks
- can use complex internetworks with multiple paths
- creates fault tolerance & load sharing
- all processing depends on following features
- router interfaces
- routing tables
- routing protocols
- access control lists


### Router Interfaces
- must have 2 or more interfaces (ports) to forard packets to other networks
- when router interface receives frame, it compares the dest MAC with interface's MAC
- if match, router strips frame header & trailer & reads packet's dest IP
- if IP maches, it proceeds the packet
- if not, router consults with routing table to determine how to get packet to dest
- process of moving packet from incoming interfce to outgoing interface called __packet forwarding__


### Routing Tables
- composed of network addr & interface pairs that telll router which interface packet shld be forwarded to
- most tables contain following for ea entry
- dest network - usually in CIDR notation
- next hop - indicates interface name/addr of next router in path to dest
- total num of routers a packet must travel through called __hop count__
- metric - numeric val that tells router how far away dest network is
- AKA cost or distance
- how route derived - tells you how route gets into routing table (1 of 3 ways)
- network connected directly
- admin enters route info manually
- AKA __static route__
- route info entered dynamically via __routing protocol__
- timestamp - tells router how long since the routing protocol updated the dynamic route


### Routing Protocols
- set of rules that routers use to exchange info so all routers have accurate info abt internetwork to populate their routing tables
- 2 main types of protocols
- dist-vector protocols
- link-state protocols


- __speed of convergence__ - how fast routing tables of all routers in internetwork updated when change in network occurs

- __interior gateway protocols (IGP)__ used in __autonomous system (AS)__
- AS - internetwork managed by single org
- routing protocols discussed so far are IGPs
- __exterior gateway protocols (EGP)__ used between AS
- Eg. broder gateway protocol (BGP)
- path vector routing protocol - analyses characeristics of all ASs to form nonlooping routing topology
- static routes entered in manually

#### Distance-Vector Protocols
- share info abt internetwork's status by copying router's routing table to other routers
- routers sharing network are called __neighbour__
- routing info protocol (RIP) & RIPv2 are most common

#### Link-State Protocols
- share info with other routers by sending status of all interface links to other routers
- open shortest path first (OSPF) most common

#### Routing Protocols Considerations
- does network change often?
- routing protocol good
- are there several alt paths to many of the networks in the internetwork?
- routing protocol can reroute arnd down links or congested routes automatically
- is internetwork large?
- routing protocol builds & maintains routing protocols automatically

### Access Control Lists
- set of rules configed on router's interface for specifying which addr & protocols can pass through interface & to whcih dests
- when ACL blks packet, its called __packet filtering__
- usually configd to blk traffic based on
- inbound/outbound traffic
- src addr
- dest addr
- protocol
- addr can be specific IP addr or network nums & filtering can be done on either src/dest addr or both

Wireless Access Points (WAP) in Depth
---
- 3 devices in 1
- wireless AP
- router
- switch

### Basic Wireless Settings
- wireless network mode
- allows you to choose which 802.11 standard AP shld operate under
- wireless network name (SSID)
- when AP is shipped SSID is set to default
- pls change it
- wireless channel
- recommended set channels 5 chann apart
- Eg. 1, 6 & 11
- SSID broadcast status
- by default, APs configed to transmit the SSID so any wireless device in range can see network

### Wireless Security Options
- encryption - all private networks shld use
- common protocols
- wired equivalent privacy (WEP)
- wifi protected access (WPA)
- WPA2
- use highest lvl of security your systems support
- all device must use same protocol
- auth - users enter user & password to access wireless network
- APs that support auth usually support remote dial-in user service (RADIUS) protocol
- MAC filtering - enables you to restrict which devices can connect to AP
- & MAC of wireless devices allowed to access network to a list on AP
- AP Isolation - creates seperate virtual network for ea client conn
- clients can access internet but cant comm with ea other

### Advanced Wireless Settings
- adjustable transmit power
- control power & range of wireless signal
- multiple SSIDs
- 2 or more wireless networks can be created with diff security settings
- vlan support
- assign wireless networks to wired vlan
- traffic priority
- if AP configed for multiple networks, can assign priority to packets coming from ea network
- wifi multimedia
- provides quality of service (QoS) settings for multimedia traffic
- gives priority to streaming audio/video
- AP modes
- AP can set to operate as traditional AP, repeater or wireless bridge

NIC in Depth
---
- NIC makes conn between comp & network medium
- perf & reliability of NIC crucial to comp's network perf

### Advanced Features
- if NIC slow, can limit network perf
- when selecting network adapter, 1st identify phy characteristics card must match
- type of bus/tech/connector needed
- norm desktop comps with basic features usually adequate
- servers sometimes warrant these high-end features
- virtualised envs benefit from NICs with multiple ports

#### Hardware Enhancement Options
- shared adapter memory
- adapter's buffers map directly to RAM on comp
- shared system memory
- NIC's onboard processor selects region of RAM on comp & writes to it as though it were buffer space on adapter
- bus mastering
- permit network adapter to take control of comp's bus to init & manage data transfers to/from comp's memory
- RAM buffering
- NIC includes extra memory to provide temp storage for incoming/outgoing network data that arrives at NIC faster than it can be sent out
- onboard co-processors
- enable card to process incoming & outgoing network data w/o requiring service from CPU
- QOS allow pripritising time-sensitive data
- auto link aggregation
- enable you to install multiple NICs in 1 comp & aggregate bandwidth
- improved fault tolerance
- by installing 2nd NIC
- failure of primary NIC shifts network traffic to 2nd NIC
- advanced config power management interface (ACPI)
- offers wake-up LAN
- allow admin to power on PC remotely by accessing NIC through network
- preboot execution environment (PXE) adapter
- allow comp to download OS instead of booting from local hard drive
- used on diskless workstations (thin clients) that dont store OS locally

Firewall
---
- security device that puts up barrier between local network & internet
- acts as filter, allowing/restricting data traffic between network/other networks
- flexible
- allows you to modify the blking rules by
- IP
- protocol (TCP, UDP, ICMP)
- port
- or for software apps & services

### Router VS Firewall

### Hardware VS Software Firewall
- both protect from malicious traffic
- hardware firewall can be stand-alone device or part of router
- such router is simple & effective protection solution for network
- reviews headers of data packets & decides if can be trusted
- if think packet safe, forward
- else, drop
- software firewall - program that you install on comp
- can be part of antivirus suit or separate
- protect from uncontrolled access to comp
- depending on software can keep safe from trojans & worms too
- differences
- it will only protect the device with the firewall installed
- have to install on all devices to be protected
- will run in background - use up system resources
- lead to slowdowns

Summary
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###### tags: `NETF` `DISM` `School` `Notes`