Lecture 6 Flashcards
Network Layer
What are the 2 primary responsibilities of the router?
- To run routing algorithms and protocols
- To forward datagrams from incoming links to the correct outgoing links
What happens if the datagrams arrive faster than they can be forwarded?
Queuing occurs.
What are the input port functions?
- Line termination
- Data link processing
- Lookup and forwarding
What are the output port functions?
- Buffer management
- Data a link processing
- Line termination
What are the 3 main components of the Internet Network layer?
- IP
- Routing protocols
- Internet Control Message Protocol (ICMP)
What is contained in a datagram?
- IP Version number (4 bits)
- Number to determine the size of the header of the datagram (4 bits)
- Type of service to allow different types of IO datagrams (8 bits)
- Datagram length indicator (16 bits)
- 16 bit identifier
- Flags (3 bits)
- 13 bit Fragmentation offset
- Time to live (8 bits)
- Upper layer protocol (8 bits)
- Header checksum (16 bits)
- 32 bit Source IP address
- 32 bit Destination IP address
- Options, if any (32 bits)
- Data (32 bits)
What is the Time-to-live in a datagram?
A field to ensure that the datagram does not circulate forever. Each router it visits will decrement this value until it reaches zero, when it is dropped.
What is the Upper-layer protocol field in the datagram?
It indicates the specific transport layer protocol to which the data portion of this datagram should be passed to.
What is datagram fragmentation?
When a datagram cannot be sent through a link because it is too big, so it gets split up into multiple datagrams to fit through the link. The datagram is reassembled afterwards.
How does the receiver know which fragments to reassemble into a datagram?
Related datagram segments have header bits that identify them as part of the same datagram.
What is the maximum transmission unit fo the ethernet?
1500 bytes.
How many bits long is IPv4?
32 bits.
What it an interface (PS: it is not an user interface)?
A connection between a host or router and the physucal link. Interfaces have an associated IP address.
Routers can only have one interface?
TRUE or FALSE
FALSE.
Routers can have multiple interfaces running at the same time.
Hosts only have one interface?
TRUE.
This is generally the case with hosts.
Hosts only have one interface?
TRUE.
This is generally the case with hosts.
What do higher-order bit and lower-order bit IP addresses determine in a network?
Higher order bit IP addresses signify the sub networks in a network.
Lower order bit IP addresses signify the interfaces in a network.
Interfaces can only communicate directly if they are on the Same network.
TRUE or FALSE
TRUE.
Interfaces on the same network share the same subnet portion of there IP address to indicate the belong to the same network.
How do when know how many bits of the IP address of an interface identify the subnet it is a part of?
Using slash notation. A slash comes after the IP address and shows the bit length of the subnet portion of said IP:
223.1.1.0/24
Has a 24 bit long subnet section.
What are two disadvantages of xlassful addressing?
- It is not very flexible - only has three options
2. Inefficient use of address space - a class might not use all the space in the address
What is the format of Classful InterDonain Routing (CIDR) address?
a.b.c.d/x
Where a, b, c and d are bits in the address and x is the number of bits in the network part of the address.
Network space is not fixed by byte boundaries, and is thus not dynamic.
What is address aggregation?
IP address are assigned to ISP (Internet service providers) in contiguous blocks. The ISPs can use these IPs for there service.
There are many addresses with the first part corresponding to:
199.31.x.x
Where the xs are other parts of the IP.
What is the advantage if address aggregation?
It allows for efficient routing between subnets, due to these division of of subnets.
What are IP addresses managed by?
The Internet Coporation for Assigned Names and Numbers (ICANN).