Network Layer Flashcards
What is forwarding?
Forwarding involves the transfer of data from an incoming link to an outgoing link with a single router
What is routing?
Routing involves all of the network’s routers who’s collective interactions via routing determine the paths that packets take.
What is a forwarding table?
Every router has a forwarding table which it uses to look up one of the header values of each arriving packet in its table. The value stored in this table indicates the outgoing link that the packet should be sent to.
What is the network service model?
The network service model defines the characteristics of end-end transport of packets between systems
What is best-effort service?
Best-effort service is the only service offered by the Internet. In best effort service no packets are guaranteed to arrive in order, within a certain time frame, or at all.
What is ATM CBR service?
CBR stands for constant bit rate.Cells are carried across a network in such a way that all cells lost or delivered late are guaranteed to be less than a specified value/
What is ATM ABR service?
ABR stands for Available Bit Rate which guarantees that packets that do arrive arrive in order.
What are the four router components and what do they do?
Input ports:
In the input port is where the lookup in the forwarding table happens. Control packets are forwarded from an input port to the routing processor
Switching fabric:
The switching fabric connects the input port to the output port.
Output ports:
Transmits packets to the outgoing link by performing link layer and physical layer functions.
Routing processor:
Executes routing protocols, maintains routing tables, attaches link state information and computes the forwarding table
What is the operating time of the forwarding data plane vs the routing control plane?
the forwarding data plane operates in nanoseconds and the routing control plane only operates in milliseconds.
List and describe the key fields of the datagram/
Version number:
The version number of the IP protocol that should be used with this datagram.
Header length:
The length of the header in bytes
Type of service:
Indicates the type of service (ex real time vs non-real time)
Datagram length: Total datagram length
Identifier, flags, fragmentation offset: flags that have to do with IP fragmentation
Time to live; the number of routers a datagram may pass through before it is dropped.
Protocol: Only used at the final destination, this field indicates what protocol should be used at the transport layer
Header checksum: checks for bit errors
Source and Destination IP address: where the datagram came from and where its going
Options: allows the datagram header to be extended
Data: payload.
What is an MTU?
A maximum transmission unit. It dictates the maximum amount of data that a link-layer frame can transmit
How does a router deal with fragmentation?
It doesn’t. A router will break a datagram into smaller outgoing pieces but will not reassemble one. Instead it is up to the destination end system to reassemble the fragments.
How does an end system reassemble fragments?
The end systems uses information in the datagram header to identify datagrams that are fragments by looking at the identification numbers, it identifies the last datagram fragment by checking if the flag bit is set to zero, and it identifies which datagram is which by looking at the fragmentation offset of each datagram.
The datagram will be passed to the transport layer only after it has been completely reassembled. If it remains incomplete, then the datagram will be discarded.
What is the Jolt2 attack?
A DoS attack where the attacker sends a flood of datagrams with the flag bit sent to 1 and the host is unable to put together the series of malicious datagrams
How big is an IP address and in what notation are they typically written?
32bits long. Dotted decimal notation, each byte is written in decimal form and separated by a period from other bytes.
