Slide 4 Flashcards
What is Routing ?
Determine route taken by packets from source to destination using routing algorithms, like planning a trip from source to destination.
What is Forwarding ?
Move packets from router’s input to appropriate router output, like the process of getting through a single interchange.
What are the components of IP addresses ?
- NetID, Network identification;
- HostID, Station’s interface identification.
What is IP Addressing: CIDR ?
CIDR: Classless InterDomain Routing
a.b.c.d/X where X is the number of bits in the subnet portion of the address.
200.23.26.0/23
|11001000 00010111 0001000 [first 23 bits]|0 00000000 [last 9 bits]
The first one is the subnet part and the last one is the host part.
What is an Interface ?
It’s the connection between host/router and a physical link, a router typically has multiple interfaces while a host only has one.
What is subnet ?
Detach each interface from its router or host creating “islands” of isolated networks, each isolated network is a subnet.
Which one are the special IPV4 addresses ?
All the addresses starting with 127 are special, because they are reserved to reference the station itself;
Addresses with all the “station” bits set to 0 represent the network address, for example 193.136.128.41 belongs to network 193.136.128.0/24.
Addresses with all the “station” bits set to 1 represent the broadcast address, like 193.136.128.255.
What is the strategy in IP fragmentation and Reassembly
Strategy:
- Fragment when needed;
- Refragmentation is possible;
- Each fragment composes a datagram (same ID);
- Reconstruction is only done at the destination;
- Offset iodinates the number of previous fragments bytes, in multiples of 8 bytes.
Example How to split 4000 byte datagram with MTU 1500 bytes ?
total length = 1500 = IPheader(20) + 1480 (data)
offset = 1480 / 8 = 185.
Every divided datagram will have the same ID and the data for the second packet will start at byte 185 x 8 = 1480 .
For the third datagram the offset will be 370 because 1480 * 2 = 2960/ 8 = 370.
NOTE: THE SIZE OF A FRAGMENT MUST ALWAYS BE A MULTIPLE OF 8 (except the last).
What is ICMP ?
The Internet Control Message Protocol, is inside the IP datagram as the network layer is below the transport layer. It is used by hosts and routers to communicate network-level information, like unreachable host, network, port or protocol, or echo request/reply.
It contains the type and the code.
How do I get an IP address ?
You use DHCP (Dynamic Host Configuration Protocol), it allows you to have a dynamic address.
What is the goal of DHCP ?
Its goal is to allow host do dynamically obtain its IP address from a network when it joins the network.
What are the DHCP messages ?
- The host broadcasts to 255.255.255.255 the “DHCP discover” message;
- DHCP server responds with “DHCP offer” message;
- Host requests IP address with “DHCP request” message;
- DHCP server sends address using “DHCP ACK” message.
Note that if the host remembers and wishes to reuse a previous IP the first two messages are skipped.
What is the objective of NAT ?
It allows a local network to use a set of private addresses for communication inside the network.
Communication to outside the private network uses a set of (at least one) global IP address.
All inside addresses are hidden from the outside, so increased security.
What are IPv6 addresses?
- They are represented with 128 bit;
- Auto-configuration of addresses;
- Simples and more efficient;
