217 Midterm Prep Flashcards
(98 cards)
1
Q
Describe OSPF
Lecture 2
A
OSPF (Open Shortest Path First) is a link-state routing protocol that was devleoped as an alternative for RIP.
OSPF uses areas to define its routing protocol. A network can be divided into distinct areas to control routing update traffic.
2
Q
Why is OSPF used over other routing protocols?
Lecture 2
A
OSPF offers Faster convergence and is more scalable which makes it ideal to be used in larger networks.
3
Q
What are the 5 exchange packets used by OSPF?
Lecture 2
A
- Hello PAcket
- Database description packet
- Link-state request packet
- Link-state Update Packet
- Link-state acknowledgment packet
4
Q
What are the 3 OSPF databases?
Lecture 2
A
- Adjacency Database - unique ists of all neighboring routers directly connected to the OSPF router (neighbor table)
- Link-State Database - Lists information about all other routers in a network. Should match on all connected routers. (topology table)
- Forwarding Database - list of routes generated by a link-state algorithm (routing table)
5
Q
What is the name of the algorithm that helps build the OSPF topology table?
Lecture 2
A
Dijkstra Shortest-Path First (SPF) Algorithm.
6
Q
How does the SPF Algorithm build a topology table?
Lecture 2
A
The SPF algorithm creates an SPF tree by placing each router at the root of the tree, and then calculating the shortest path to each node. This is how the best routes are determined by the router.
Once the best paths are determined, they are stored in a forwarding database and then used to create the routing table.
7
Q
Describe the 5 steps of link-state routing.
Lecture 2
A
- Neghibor Adjacencies are Established
- Link-State Advertisements are echanged
- The link-state database is built
- The SPF algorithm begins determining the best paths for routing
- Once the best route is chosen, routing begins.
8
Q
Define Single and Multarea OSPF
Lecture 2
A
- Single-Area OSPF is OSPF routing where all routers are in a single area.
- Multiarea OSPF is OSPF routing where the routing domain is divided up into segmented zones.
9
Q
Define Single and Multarea OSPF
Lecture 2
A
- Single-Area OSPF is OSPF routing where all routers are in a single area.
- Multiarea OSPF is OSPF routing where the routing domain is divided up into segmented zones.
10
Q
What are some of the advantages of Multiarea OSPF?
Lecture 2
A
- Smaller routing tables are kept because less routes are used. Network addresses are allowed to be summarized by the area they are in
- Reduced Linke-State Update Overhead. OSPF with smaller areas ends up using less processing power and memory
- Reduced Frequency of SPF Calculations. Impacts of topology changes are localized within a single area.
11
Q
What is OSPF v3
Lecture 2
A
OSPFv3 is the IPv6 verision of OSPFv2.
While it is possible to do IPv6 rouing using OSPFv2, the routing is done in seperate instances. OSPFv3 allows you to similtaniously configure both IPv4 and IPv6 . `
12
Q
List and describe the 5 different OSPF link state packets.
Lecture 2
A
- Hello - Used for neighbor discovery and the creation of adjacencies
- Database Description (DBD) - Checks for database synchonization between devices
- Link-State Request (LSR) - REquest specific link-state records from router to router
- LInk-State Update - Sends specifically requested link-state records
- Link-State Acknowledgment - Acknowledges other packet types.
13
Q
Name some functions of the OSPF Type 1 Hello Packet
Lecture 1
A
Hello Packets:
* Discover OSPF neighbors and establish neighbor adjacencies
* Advertise parameters on which two routers must agree to become neighbors
* Elect the DR (Designated Router) and the BDR (Backup Designated Router) on multiaccess networks.
14
Q
Name the operational states of OSPF
Lecture 2
A
- Down State - No hello packets received
- Init State - Hello packets received
- Two-Way State - Bidirectional state where communication has been established
- ExStart State - the Database Description packet exchange sequence begins
- Exchange State - DBD Packets are exchanged
- Loading State - LSRs and LSUs give specific routing information between routers. The SPF algorithm is used to find the best routes
- Full-State - Routers are both Synchronized
15
Q
Dedscribe the 3 step process of the Database Desynchronization state
Lecture 2
A
- The router with the highest ID sends its DBD flag first putting it into the ExStart state
- The router then exchanges its database description(s) with other routers to compare known adjacencies
- A Link-State request is sent out, comparing DBD information with local DB information. If another router has new information, the receiving router chagnes to a loading state.
16
Q
When are Link-State Requests sent to routers?
Lecture 2
A
Whever a change is perceived in a routers database
OR
Every 30 Minutes
17
Q
What are the 2 multiaccess network problems that designating a DR helps solve?
Lecture 2
A
- Multiple adjacencies creation. DRs prevent an excessive number of LSAs being exchanged between routers on a network
- Extensive flooding of LSAs - Every time OSPF is utilized, LSAs are flooded. Too much flooding can bog down a network.
18
Q
What is the purpose of assigning a router ID?
Lecture 3A
A
Router ID’s participate in the synchronization of OSPF databases. The router with the highest ID sends the DBD packets before anybody else does.
Router IDs are also used to elect
the DR.
19
Q
How are router ID’s formatted?
Lecture 3A
A
Router IDs are a 32 bit value represented as an IPv4 address. A router requires an RID to participate in OSPF. If a router ID isn’t manually assigned, it is automatically determined based on the IP address of the router.
20
Q
Describe the Router ID order of precedence.
Lecture 3A
A
- The router ID has been explicitly configured by an administrator
- The router chooses the highest IPv4 of any configured loopback address.
- The router chooses the highest active IPv4 address of any of its physical interfaces.
21
Q
What is a Wildcard Mask?
Lecture 3
A
A wildcard mask is the inverse of a subnet mask configured on an interface.
An easy way to determine a wild card mask is to subtract your subnet mask from 255.255.255.255.
Example:
The Wildcard mask for a /24 address is 255.255.255.255 - 255.255.255.0 which would be 0.0.0.255
22
Q
What is the purpose of using a Passive Interface when configuring OSPF?
Lecture 3A
A
If you do not configure a passive interface, OSPF will waste resources by sending messages into a lan where no routers need OSPF information. This can affect the network by:
Wasting bandwidth and resources
Harming security by sending unnessecary packets that can be picked up by packet sniffing software. (but they would have already infiltrated your lan so i don’t get how this is a security risk but whatever lol)
23
Q
What do DRs, BDRs and DROTHERs do?
Lecture 3A
A
A DR is responsible for collecting and distributing LSAs.
A BDR is a backup incase something happens to the DR. Passively listens and maintains a relationship with all connected routers, and in the event that the DR fails, It is elected to the role of DR.
DROTHERs are all other routers on a network.
24
Q
Describe the 5 DR/BDR neighbor states in multiaccess networks
Lecture 3A
A
- FULL/DROTHER The DR/BDR is fully adjacent with a DROTHER router.
- FULL/DR This router is fully adjacent with a DR neighbor.
- FULL/BDR This router is fully adjacent with a BDR neighbor
- 2-WAY/DROTHER A DROTHER has a neighbor relationship with another DROTHER, and they exchange hello packets between eachother.
The default normal state of an OSPF router is FULL. The only exception to this rule is the 2WAY state.
25
Describe the DR/BDR election process
| Lecture 3A
1. The router with the highest interface priority is elected as the DR.
2. If the interface priority value is set to 0, that interface can not be the DR or the BDR
3. The default priority is 1, and can be set to any number between 0-255
4. If the interface priorities are equal, the router with the highest router ID becomes the DR, and the second highest becomes the BDR.
26
Define OSPF Cost Metrics.
| Lecture 3A
The OSPF cost metric is how routers determine the best path across a network. The LOWER the cost the BETTER the path (like golf swings)
27
What is the formula used to calculate OSPF Cost Metrics?
| Lecture 3A
Cost = Reference bandwidth / interface bandwidth
## Footnote
image for some examples
28
What are dead intervals?
| Lecture 3A
Dead intervals are the period a router waits to receive a hello packet before declaring the neighbor down.
The default length of a dead interval is 4 times the Hello interval.
29
Why would you want to manually set the OSPF cost value?
| Lecture 3A
1. Administrators may want to manually influence path selection within OSPF
2. Equipment connected to your router may use a different OSPF calculation formula, and you might need to make them match with eachother for conectivity.
30
Name and describe some basic OSPF verification commands.
| Lecture 3A
* show ip interface brief - This verifies that the desired interfaces are active with correct IP addressing.
* show ip route- This verifies that the routing table contains all the expected routes.
* show ip ospf neighbor
* show ip protocols
* show ip ospf
* show ip ospf interface
| Just copy/pasted these from the lecture slides.
31
Define Bandwidth, Congestion, Delay and Jitter and describe how the affect Network Transmission Quality
| Lecture 4
* Bandwidth is the measured number of bits that can be transmitted in a single second (BPS)
* Congestion is when a delay is caused by a network having more traffic than it can handle at a given point in time.
* Delay or Latency refers to the time it takes for a packet to travel to its destination.
* Jitter is the variation of delay measured from received packets.
32
Name and describe different types of network delay.
| Lecture 4
* Code Delay = The amount of time it takes to compress data at the source before transmission
* Packetization delay = The time it takes to encapsulate a packet with all necessary packet information
* Queing delay = The variable amount of time a frame or packet waits to be transmitted on the link
* Serialization Delay = The amount of time it takes to transmit a frame onto a wire
* Propogation Delay = The amount of time it takes for the frame to travel between source and destination
* De-Jitter Delay = The fixed amount of time it takes to buffer a flow of packets and then send them out in evenly spaced intervals.
33
What is the predominant type of IP traffic today?
| Lecture 4
Video traffic takes up 82% of all network traffic as of 2022.
Previously the leading traffic was voice and data traffic, but with the rise of streaming the type of traffic has evolved.
## Footnote
Mobile video traffic will reach 60.9 exabytes per month by 2022
34
Name some characterists of Voice Traffic
| Lecture 4
* Smooth
* Benign
* Drop Sensitive
* Delay Sensitive: Jitter needs to be less than or equal to 30ms. p=
* High priority traffic
* Requires at least 30kbps of bandwidth.
* Uses RTP Ports 16384-32767
35
Name some characteristics of Video Traffic
| Lecture 4
* Transmits in bursts
* High volume
* Drop Sensitive / Delay Sensitive
* High Priority Traffice
* Used UDP o ports as well as Real-Time Streaming Protocols.
36
Name some characteristics of Data Trafic
| Lecture 4
* Uses TCP to prevent loss of important data such as email or web pages
* Can be smooth or in bursts
* Insensitive to delay, the data arriving in its original format is more important than the data arriving quickly.
37
Define queuing
| Lecture 4
Queuing is a method of managing congestion that can buffer, prioritize, and require packets before being transmitted.
Queuing algorithms include:
* First-In First-Out (FIFO)
* Weighted Fair Queuing (WFQ)
* Class-Based WFQ
* Low Latency Queuing (LLQ)
38
Describe FIFO Queuing
| Lecture 4
FIFO buffers and forwards packets in order as they arive (Hence the name first in first out)
FIFO contains no concept of priority or classes, and makes no decisions based on packet priority. All packets are in a single queue and treated equally.
39
Describe Weighted Fair Queuing
| Lecture 4
WFQ is an automated scheduling algorithm that allocates fair bandwidth to all network traffic.
WFQ applies priority to identified traffic, classes it into flows, and determins how much bandwidth should be used by each flow.
WFQ defines flows based on source and destination IP, MAC, port numbers, Protocols, and ToS values.
40
Define Class Based WFQ
| Lecture 4
CBWFQ extends standard WFQ to provide support for user-defined traffic classes.
Packets satisfying match criteria for a class constitute traffic for that class.
A class can be assigned characteristics by a user such as bandwidth, weight, and maximum packet limit. Bandwidth assigned to a class is guaranteed to be delivered during periods of congestion.
41
Define Low Latency Queuing
| Lecture 4
LLQ brings strict priority queuing to CBWFQ.
Strict PQ allows delay-sensitive packets such as voice to be sent before packets in other queues.
LLQ allows delay-sensitive packets to be sent first, giving them preferential treatment over other traffic.
## Footnote
Cisco recommends only giving PQ to Voice Traffic.
42
What are the 3 QoS Policy Models?
| Lecture 4
1. Best Effort
2. Integrated Services (IntServ)
3. Differentiated Services (DiffServ)
43
What are the benefits and Drawbacks of the Best Effort QoS Policy?
| Lecture 4
The best effort model treats all network packets equally.
Benefits:
* Most Scalable
* No special QoS Mechanisms required
* Easiest and quickest to depoy
Drawbacks
* No guarentees your packets are delivered
* Packets arrive whenever they can and in any order possible
* No preferential treatment for important packets
* Critical and Non-Critical data are treated the same.
44
What are the characteristics of using the IntServ QoS Model?
| Lecture 4
IntServ delivers end-to-end QoS that real-time applications require.
IntServ:
* Explicitly manages network resources
* Uses Resource Reservation and Admission Control mechanisms as building blocks to establish and maintain QoS
Uses a connection oriented approach
IntServ severely limits the scalability of a network.
45
What are the characteristics of using the DiffServ QoS Model?
| Lecture 4
DiffServ specifies a simple, scalable mechanism for classifying and managing network traffic
DiffServ is not end-toend because it can not enforce end-to-end guarantees (if you can translate this for me I will be eternally grateful)
Hosts forward traffic to a router which classifies the flows into aggregates (or classes idk why he gotta be fancy on us) and provides appropriate QoS policy for each class.
46
What are the 3 approaches listed in the lecture slides for preventing packet loss?
| Lecture 4
1. Increasing Link Capacity to ease or prevent congestion
2. Increasing Buffer Space to accommodate bursts of traffic from other more fragile data flows
3. Dropping lower priority packets first before congestion occurs.
47
Name and describe the 3 categories of QoS tools
| Lecture 4
1. Classification and Marking tools. These tools are used to analyze traffic and determine what class they should belong to. Once class has been determined, the packets are marked
2. Congestion Avoidance Tools. Traffic classes are alloted their own portions of network resources defined by the QoS Policy.
3. Congestion Management Tools. When traffic exceeds the resources available to a network, traffic is queued to await the availability of resources.
48
Describe some of the issues with Single-Area OSPF configurations?
| Lecture 3B
Single Area OSPF has larger routing table and Link-State Databases. They also have more frequenty SPF algorithm calculations. This requires more memory on the routers, and creates unnessecary traffic that bogs down a network.
Multi-Area OSPF is used to make these networks more scaliable.
49
Describe Multi-Area OSPF and its advantages
| Lecture 3B
Multiarea OSPF is defined by taking a large OSPF area, and dividing it into smaller, individually managed areas.
Multiarea OSPF requires less memory and processing power, and a hierarchical design to operate properly.
The advantages include smaller routing tables, reduced link-state overhead, and reduced frequency of SPF calculation.
50
Describe the two layer Multilayer hierarchy.
| Lecture 3B
Layer 1 - The Backbone (transit Area). This area's primary function is the fast andd efficient movement of packets. This is usually area 0.
Layer 2 are the non backbone area(s). These connect users and resources to eachother.
Usually are set up along functional or geographical groupings.
All traffic from Regular Non backbone areas MUST travel across a backbone area.
51
Name and describe the 4 different OSPF router types.
| Lecture 3B
1. Internal Router - All interfaces are in the same area
2. Backbone Router - Router that resides in the backbone area (area 0)
3. Area Border Router (ABR) - Router that has interfaces in multiple different areas
4. Autonomous System Boundary Router - A router that has at least one interface attached to an external network.
Routers can be classified as more than one router type.
52
Describe the general purposes of LANs
| Lecture 5
LANs provide networking service inside of a small geographical area.
They are used to interconnect local devices.
Usually LANs are owned by an organization or a home user.
Free to use once the infrastructure is up
Provide High bandwidth speeds with ethernet and Wi-Fi services.
53
Describe the general purposes of WANs
| Lecture 5
WANS operate over a large geographic area.
They are used to interconnect remote sites (or LANS)
WANS are ususally owned and managed by service providers.
WANS offer low to high bandwidth speeds over long distances.
54
What is the difference between private and public WANs?
| Lecture 5
Private wants provide a guarenteed service level with consistent bandwidth speeds and security.
Public WANs are controlled by ISPs using the internet, so speeds will vary and security is not guarenteed
| .
55
What are the 5 WAN topologies mentioned in the lecture slides?
| Lecture 5
* Point to Point - Connection between 2 end points.
* Hub and Spoke. A single hub router connects to multiple spoke routers. All the spoke routers connect to eachother through the hub. Single point of failure, if the hub goes down, the network is lost.
* Dual-homed Dual homed offers enhanced redundancy, load balancing, and backup connections. More expensive than previous topologies, this network has 2 hubs, which forces complex configurations, but provides a higher level of service.
* Fully Meshed - Multiple Virtual circuts connect all sites in the network, allowing for full fault tolerance.
* Partially meshed. Most sites are connected through a mesh, but some are not included.
56
Describe how WAN organizations communicate with Carriers.
| Lecture 5
Organizations sign a service level agreement with a service provider.
The service provier may or may not be the actual carrier.
Carriers own and maintain physical connections between the provider and the customer.
Organization-----> ISP------->Carrier
57
Describe single and dual carrier connectoins.
| Lecture 5
Single-Carrier connections are when an organization has an exclusive partnership with a single service provider. The SLA is negotiated between the Service provider and the organization only.
A dual-carrier connection provides redundancy by negotiating seperate SLAs with two service providers.
58
Describe how a network evolves from small to distributed.
| Lecture 5
1. Network starts as a small single LAN network. IT support and network connections all come from a Digital Subscriber Line
2. Network grows into a CAN (Campus ARea Network) once they move from a single-floor small office, to a larger building with multiple floors. Firewalls secure internet access, and IT support is hired on as part of the staff.
3. The organization now spans multiple buildings and requires the use of a MAN (Metropolitan Area Network) to connect to multiple sites within a city. The central office is the main hub, while branch offices provided dedicated lines through a local ISP.
4. Finally, the network has expanded world wide. Site to Site VPNs are used to allow secure internet access from around the world.
| I doubt we will have to care about this but added just in case.
59
Name some WAN Standards Organizations.
| Lecture 5
TIA/EIA
ISO
IEEE
ITU-T
3GPP
60
Name some WAN standards that are associated with the Physical and Data Link Layers
| Lecture 5
Layer 1 (Physical) protocols
* Synchronous Digital Hierarchy (SDH)
* Synchonous Optical Networking (SONET)
* Dense Wavelength Division Multiplexing (DWDM) aka Layer 0
* Optical Transport Network (OTN)
Layer 2 Protocols
* Broadband (i.e., DSL and Cable)
* Ethernet WAN (Metro Ethernet)
* Multiprotocol Label Switching (MPLS) – Layer 2.5
* Point-to-Point Protocol (PPP) (less used)
* High-Level Data Link Control (HDLC) (less used)
* Frame Relay (legacy)
* Asynchronous Transfer Mode (ATM) (legacy)
61
Name some WAN devices described in the lecture notes.
| Lecture 5
* Voicemand Modem - Dial up modem. Not used
* DSL / Cable modem - High speed modems that connect to the DTE router using Ethernet
* CSU/DSU - Connects a digital device to a digital line.
* Optical Converter - Connects fiber-optic media to copper and convers optical signals to electric pulses
* Wireless Router / AP - Used to wirelessly connect to a WAN provider
* WAN Core devices - WAN's backbone consists of multiple routers and layer 3 switches
62
Describe Serial Communication
| Lecture 5
Serial communication transmits bits sequentially over a single cahnnel.
Parallel communications transmit several bits over multiple wires.
As cable length increases, timing between channels becomes more ensitive to distances. So PArallel communication is limited to shorter range communication.
63
Describe circuit-Switched Communication.
| Lecture 5
Circuit Switched networks establish a dedicated channel between endpoints before the users are able to communicate.
Dedicated virtual connections via the service provider network are established before communications start.
All communication follows along the same path.
64
Describe Packet-Switched communication.
| Lecture 5
Most common form of network communication.
Data traffic is segmented into packets that are routed over a shared network.
Less expensive and more flexible than circuit switching.
Common WAN technologies that use packet switching are:
* Ethernet WAN (Metro Ethernet)
* Multiprotocol Lable Switching (MPLS)
* Frame Relay
* Asynchronous Transfer Mode (ATM)
65
Describe legacy Circuit-Switch WAN connectivity options
| Lecture 5
Public Service Telephone Network (PSTN) used Dialup to allow for WAN connections. Traditional Local Loops supported binary computer data through the telephony network using a voiceband modem. Speed was less than 56 kbps.
Integrated Services Digital Network (ISDN) used sircuit switching technology to enable PSTN local loops to carry digital signals. Higher speed and capacity than dialup. Speeds were between 45kbps and 2.048mbps
66
Describe legacy Packet-Switch WAN connectivity options.
| Lecture 5
Frame Relay is a simple Layer 2 Non-broadcast multi-access WAN technology used to interconnect LANs.
Asynchronous Transfer Mode (ATM) is capable of transferring voice, video, and data through private and public networks.
Both have been replaced by Metro Ethernet and other more modern internet-based solutions.
67
How did legacy WANs connect to eachother?
| Lecture 5
LANs connected to a local loop of a service provider via dedicated lines or switched services through an ISP.
Lines were leased from an SP to establish connections. The main 2 systems were known as T-Carriers (NA) and E-Carriers (Europe).
68
Discuss the 3 Modern WAN connectivity options
| Lecture 5
* Dedicated broadband - Fiber installed indipendently by an organization to connect multiple remote locations. Fiber can be leased or purchased from a supplier.
* Packet Switched - Metro Ethernet replaces legacy WAN options and enables sites to connect to a provider regardless of access technology
* Internet-BAsed Broadband - Organizations are using global network infrastructure for WAN connectivity.
69
What are the benefits of using Ethernet WAN?
| Lecture 5
* Less expensive to implement
* Easy to integrate with existing networks
* Enahnced business productivity due to the high speed of fiber-optic cables
70
What is MPLS?
| Lecture 5
Multiprotocol LAbel Switching (MPLS) is a high-performance service providing WAN routhing technology to connect different clients without regard to access method.
MPLS encapsulates all types of protocols including both IPv4 and v6 traffic. Also provides services for qoS support, traffic engineering, redundancy, and VPNs.
Referred to as Layber 2.5 Technology.
71
Describe wired and wireless options of Internet Based Connectivity.
| Lecture 5
Wired Options include DSL Cable and Optical Fiber providing consistent bandwidth and reduced latency / errors.
Wireless options include Cellular, Satellite, 3g/4g/5g internet services. Wireless signals can be negatively affected by factors such as distance from internet sources, interference from other sources, and the weather.
72
What is DSL Technology?
| Lecture 5
Digital Subscriber Line (DSL) is a high-speed, constantly available conection technology that uses existing telephone lines to provide IP services to users.
DSL are categorized as either Asymmetric DSL or Symmetric DSL.
ASDL and ASDL2+ provide higher downstream bandwidth to the user.
SDSL provides the same capacity for both downstream and upload bandwidth.
73
Describe how Cable Technology can provide Internet-Based Connectivity.
| Lecture 5
Cable technology uses a high-speed always-on coaxial cable model to provide IP services from a cable company to service users.
The Data over CAble Service Interface Specification (DOCSIS) is the international standard for adding high-bandwidth data into an existing cabling infrastructure.
74
What are teh 3 types of fiber installation?
| Lecture 5
1. FTTH - Fiber to the home reaches the boundary of a residence
2. FTTB - Fiber to the building reaches the boundary of the building with the final connection to the individual living space being made via alternative means.
3. FTTN - Fiber to the Node/Neighborhood reaches an optical node that converts optical signals to an acceptable formate for twisted pair or coaxial cable on the premise.
75
Name some methods of establishing wireless internet-based broadband.
| Lecture 5
* Municipal Wi-Fi - Free high-speed wifi access available in many areas / cities
* Cellular - Used to connect devices using radio waves to communicate thorugh a nearby phone tower.
* Satellite Internet - Typically used in rural areas where cables and DSLs are not available. Routers connect to a satellite dish which communicates with a satellite in orbit.
* WiMAX - Worldwide Interoperability for Microwave Access is described in IEEE 802.16 as providing high-speed broadband service with wireless access.
76
Describe the benefits of using VPN technology
| Lecture 5
* More Secure
* Eliminates expensive dedicated WAN links
* coperations can add capacity without adding infrastructure
* Compatable with broadband technology
The two types of VPNs are:
Site to Site VPNs
Remote Access
77
What is an ACL?
| Lecture 6
An ACL (Access Control List) is a method used to filter packets based on information found in the packets header. When applied to a router interface, ACLs force the router to perform additional evaluation on all network packets as they pass through the interface.
ACLs use a sequential list of permit or deny statements known as Access Control Entries (ACEs) to determine what traffic is or isn't allowed into the network. This process is called packet filtering.
78
What are the main purposes of ACLs?
| Lecture 6
* ACLs limit network traffic to increase performance
* Provide traffic flow control
* Filter traffic based on the type of traffic.
* Provide priority to specific classes of network traffic (QoS)
* Provide a basic levle of security for network access
79
Describe Standard vs Extended ACLs
| Lecture 6
Standard ACLs only filter at Layer 3 using SOURCE IP addresses.
Extended ACLs filter at Layer 3 using the SOURCE and or DESTINATINO IPv4 address, but also have the ability to filter at Layer 4 using TCP / UDP ports as well as operational protocl type information.
80
How do inbound and outbound ACLs work?
| Lecture 6
Inboudn ACLs filter packets BEFORE they are routed to the outbound interface. An Inboudn ACL is efficient because it saves the overhead of routing lookups if the packet is discarded.
Outbound ACLs filter packets AFTER being routed regardless of the inbound interface.
81
What are the operational steps used when traffic has entered a router interface with inbound standard ACL configured?
| Lecture 6
1. The router extracts the source IPv4 address from the packet header
2. The router starts at the top of the ACL and compares the source IPv4 to each ACE in sequential order.
3. When a match is made, the router carries out the instruction, either allowing or denying the packet, and it stops analyzing ACEs.
4. If the IPv4 address is not listed in the ACL entries, the packet is discarded based on the implicit deny ACE automatically applied to all ACLs.
## Footnote
The last ACE statement is always an implicit deny that blocks all traffic. It is not openly shown in the configuration.
82
What are the rules when defining wildcard masks?
| Lecture 6
Wildcard mask bit 0 = Match the corresponding bit value in the address
Wildcard mask bit 1 = Ignore the corresponding bit value in the address.
83
What are the wildcard mask types associated with ACLs?
| Lecture 6
Wildcard to match a host
Wildcard Mask to Mwatch an IPv4 Subnet
Wildcards
84
What are the 2 Wildcard Mask Keywords in the Cisco IOS?
| Lecture 6
Host - THis keyword substitutes the 0.0.0.0 wildcard mask. This mask states that all IPv4 address bits must match to filter just one host address
ANy - THis keyword substitutes for the 255.255.255.255 mask. This mask says to ignore the entire IPv4 address or to accept any addresses.
85
What are the limitations for a single router interface when it comes to ACLs?
| Lecture 6
A router interface can only have:
* ONe outbound IPv4 ACL
* ONe Inbound IPv4 ACL
* One Inbound IPv6 ACL
* One outbound IPv6 ACL.
86
Describe some ACL Best Practices
| Lecture 6
87
Describe Numbered and Named ACLs
| Lecture 6
Numbered ACLs are based on a specific number range that correlates with either Standard or Extended ACLs.
Named ACLs are the preferred method to use when configuring ACLs. Specifically, standard and extended ACLs can be named to provide information about the purpose of the ACL.
88
Where should ACLs be placed?
| Lecture 6
Extended ACLs should be located as close as possible to the SOURCE of the traffic being filtered
Standard ACLs should be located as close to the DESTINATION as possible.
89
Describe some factors that influence ACL Placement.
| Lecture 6
The extent of organizational control - Place3ment of the ACL can depend on whether or not the organization has control of both source and destination networks.
The Bandwidth of the networks involved - It may be desirable to filter unwanted traffic at the source to prevent transmission of bandwidth-consuming traffic
Ease of configuration - It may be easier to implement an ACL at the destination, but traffic will unnecessarily be using bandwidth.
90
Describe borderless switched networks.
| Lecture 8
The Cisco Borderless Network is a network architecture that can connect anybody anywhere on any device securely, relaibly and seamlessly.
91
Why do networks need to be scaliable?
| Lecture 8
Networks need to be scaliable to be able to support:
* Converged network traffic
* Critical applications
* Diverse business needs
* Centralized administrative control
92
Describe the functions of the Access, Distribution, and Core layers of Hierarchical networks.
| Lecture 8
Access layer - Provides network access to the user. Access layer switches connect to distribution layer switches.
Distribution layer = connects to the access layer and the core layer. Impliments routing, QoS and Security.
core Layer - Network Backbone layer. Provides fault isolation and high-speed backbone connectivity.
93
Describe 2-Tier and 3-Tier Campus Networks
| Lecture 8
Three-Tier Campus networks are used by organizations requiring access, distribution and core layers. THe reccomendation is to build and Extended Start topology from a centralized building location to all other buildings on campus.
Two-Tier Campus Networks are used when seperate distribution and core layers are not required. Used for smaller campus locations.
94
What strategies are used to enable network scalability?
| Lecture 8
Scalability is accomblished by using:
1. Redundancy
2. Link Aggregation
3. Scalable Routing protocol(s)
4. Wireless Connectivity
95
How can a network administrator plan for redundancy?
| Lecture 8
1. INstall duplicate equipment
2. Provide failover services for critical devices
3. Use Redundant paths. If using redundant paths, STP must be used to prevent layer 2 looping.
96
Describe reducing failure domain size
| Lecture 8
A failure domain is the area of a network that is impacted when the network experience problems.
The function of the device that initially fails impacts a failure domain.
Routers or Layer 3 switches are deployed in pairs to avoid having a single point of failure.
97
What form factors must be considered when deciding on switch hardware?
| Lecture 8
Fixed vs Modular configuration
Stackable or non-stackable configuration.
98
Describe 2-Tier and 3-Tier Campus Networks
| Lecture 8
Three-Tier Campus networks are used by organizations requiring access, distribution and core layers. The recommendation is to build an Extended Start topology from a centralized building location to all other buildings on campus.
Two-Tier Campus Networks are used when separate distribution and core layers are not required. Used for smaller campus locations.
