Karteikarten
SCC 203 - Lecture 5 - Internet Protocol
Karten in diesem Stapel (25)
- 1What type of protocol is Internet protocol?• Connectionless network protocol
– No attempt to build path prior to transmission - 2Why is internet protocol referred to as best effort?Best-effort – packets may best
– Lost
– Delivered out of order (book)
– Duplicated
– Delayed - 3What are the key internet design options?Test before release – Require multiple working implementations
Simplicity: Avoid unnecessary features – Only accept essentials
• Modularity – e.g. protocol stack of independent layers
Support Heterogeneity
– Allow different network hardware, structures, and applications
– Avoid fixed options and parameters
• Have sender and receiver negotiate values - 4State the last 3 key internet design options according to the slides?Choose design over supporting everything
– Don’t allow one desired feature to break design
• Be strict when sending, tolerant when receiving
– Rigorously stick to standard when sending
– Expect errors in received messages
• Scalability
– Assume no centralised system will handle global load
– Spread load as evenly as possible
– Design in performance and design out cost - 5State the components of an IP packet transferred using Inter protocol version 4?version
Header length
Quality of service
Packet length
Fragmentation Control
Time to live
Next protocol
Checksum
Source IP address
Destination IP address
IP options
Payload/Data - 6What is encapsulation in networking?Encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects.
- 7What is decapsulation in networking?Decapsulation is the process of opening up encapsulated data that are usually sent in the form of packets over a communication network. It can be literally defined as the process of opening a capsule, which, in this case, refers to encapsulated or wrapped-up data.
- 8What does the version field of an IP packet have to contain?– Either 4 or 6
– Unknown values rejected - 9What is the size of the header Length field of an IP packet?Header Length
– n x 4 bytes
– More than 5 implies options
• i.e. basic header 20 bytes - 10What does the DS (Differentiated services) field identify?– Identifies priority of traffic -- Voice, file transfer, …
• Note: Use of this field has changed over the years - 11What does the Explicit Congestation Notification (ECN) field do?– Flags whether packet has experienced congestion
- 12What does the Packet length field show?Length of whole IP packet in bytes
– Includes IP header and payload
• Excludes surrounding layer 2 headers/ encapsulation - 13Max length of an IP packet?• Max length of IP packet therefore 65535 bytes
– Normally limited to 1500 bytes by Ethernet - 14What is fragmentation?The process or state of breaking or being broken into fragments
- 15State some important concepts about Transparent fragmentation?Following devices on path unaware of fragmentation -Good
• Fragments must exit network through same router - Bad
• Overhead of extra packet headers removed at exit - Good
• Ties up resources until last fragment of packet arrives - Bad - 16State some important concepts about Non-transparent fragmentation?• Standard for IP traffic
• Simplifies task of routers, penalty being
– All subsequent devices have to carry and process additional IP packet headers (more overhead) - 17What happens when a fragment is lost?Whole packet is retransmitted
- 18How can lost fragments be solved?Host/ application should therefore avoid sending large packets likely to be fragmented
– Send smaller packets -- choose small value, or…
– Find Maximum Transfer Unit (MTU) for path between source and destination - 19How does the fragment identifier work?Fragment Identifier (ID)
– Sending host uses incrementing ID in each packet
– If fragmented, this value copied to each fragment
• At receiver
– Packets with same ID belong to same source packet - 20What is the purpose of the flags field?Flags
– Don’t Fragment (DF)
• Tells devices not to fragment packet
• Device must reply with error if packet too big
– More Fragments (MF)
• Set to one for all but last fragment; 0 if only packet - 21What is the purpose of the fragment offset?• Fragment Offset
– Tells receiver where to place fragment in reconstituted packet
– Offset in 8 byte chunks
• All but last fragment must be a multiple of 8 bytes - 22What is the purpose of the TTL field (time to live) field and how does it work?It states how long a specific packet is allowed to be active for within a network.
Routers decrement TTL by
– Number of seconds spent processing packet
– At least 1
• Any packet with a TTL of 0 is discarded
– Device typically replies with TTL_EXCEEDED error - 23What does the next protocol field show?Indicates
– Protocol used to encapsulate following user data
– Determines how payload will be processed - 24State some key protocol numbers?Number - Protocol - Description
1- ICMP- Internet Control Message Protocol
2 -IGMP - Internet Group Management Protocol
6- TCP- Transmission Control Protocol
17- UDP- User Datagram Protocol - 25How is Checksum wrong? https://www.youtube.com/watch?v=dXartoyj2owWe calculate sum and send its complement
• When we calculate sum at receiver
– We’re getting orig. sum + complement of sum
– If we don’t get 0xffff we must have an error
Informationen
- Beschreibung
- Karteikarten am SCC 203 - Lecture 5 - Internet Protocol, erstellt von Ayo Olutobi am 31/01/2017.
- Erstellt von
- Ayo Olutobi
- Aufrufe
- 0
- Bewertung