IP addresses Flashcards
what does IPV4 use
octets(group of 8 bits) and its a 32 bit number
summarise unusable/reserved addresses
- some IP addresses cannot be used for an individual network or host
eg: - 127.x.x.x, non routable addresses, used for diagnostics within local network
- x.x.x.0 is the network identifier
- x.x.x.255 is reserved as the broadcast address on that subnet, where data is sent simultaneously to all subnetwork hosts
- x.x.x.1 is the default router address
parts of an IP address
networkID - left hand bits used to define the network where nodes are communicating
HostID - right hand bits, used to identify the nodes on the network
summarise classful addressing
when the network ID is given at the end of the IP address, eg 210.54.101.0/24 has a network ID of 24
summarise classful IP addressing
IP addresses being categorised into classes to identify network ID and host IDs of various ranges
summarise subnet masking
- a subnet mask is used with an IP add to identify the 2 unique parts of the address
- subnet mask has all network ID bits set to 1, and all host IDs set to 0
- bitwise AND is used with the IP and the network is identified
summarise subnetting
- an organisation can create subnetwork segments within their IP network in order to ease management
advantages of subnetting
- improves efficiency by routing data through one segment only
- reduces the size of the broadcast domain, which can improve security
- can reduce data collisions
public vs private IPs
- public IPs must be globally unique, and be able to be addressed directly by any computer
- priv IPs do not need to be globally unique and dont require internet registry
following are considered private:
- 10.0.0.1 - 10.255.255
advantages of private IPs
reduces the need for every computer to have its own unique public address
number of possible hosts
2^32 - 2
because they cane end in 255 or 0
summarise network address translation (NAT)
- used to convert IP addresses as they pass between a public address space (using a public IP ) and an LAN with a priv address space
- they are required to translate private IPs as they are not routable , therefore cant be used for routing packets on the Internet
advantages of NAT
allows a single public IP address to be shared by any number of hosts with a private IP
NAT process
- the translation device records the source and destination socket address for each request
- it then communicates on the hosts with the destination IP address
- when a response returns, it is passed back to the host that made the original request
what is port forwarding
- a networking technique used to redirect communication requests from one address and port number to another
- while the packets are traversing a network
- typically through a router or firewall
- Allows external devices to access services on a private network.
what is the purpose of a DHCP system
to automate the configuration of hosts connecting to a TCIP/IP network
advantages of a dhcp system
- reduces the need for expert knowledge when configuring a host
- reduced the time required to configure host
- facilitates efficient use of a limited pool of IP addresses
how does a DHCP system work
- The host sends a request to discover a DHCP server
- DHCP servers offer configuration to host
- host accepts offer of configuration from server
- DHCP server confirms that configuration has been allocated to host.
- The host configures its network interface using the IP address and configuration details provided by the server.
explain how an external router would be configured so that a web server can be accessed by computers outside of the network
- traffic arriving on the HTTP port must be forwarded by
- the external router to the IP address of the web server
Explain how:
* Computer A will use a subnet mask to determine whether or not it can send the
packet directly to Computer B across the LAN or if the packet must be sent via the
Internet
- AND operation of subnet mask with Computer A’s IP address
- AND operation of subnet mask with Computer B’s IP address
- result (of each AND operation) is the network/subnet ID
- network/subnet IDs compared
- as they are different, then packet must be sent via gateway, Computer B is not on the same subnet
- if they were the same, then Computer B
is on the same subnet.
explain how a packet will be routed across the Internet
- hierarchical organisation of routers
- path to take selected by each router
- (possible) repackaging of packet to use different protocol
- use of router tables to determine next hop
- router decrementing “time to live” of packet
- route determined using IP addresses
how can the checksum be used to determine if the received packet has been changed
during the transmission.
checksum produced when packet transmitted
* (hash) value calculated from packet contents
* this value appended to packet
* computer B recalculates checksum
* received and calculate checksum compared
* if these match packet contents/data are accurate . if these differ the data has been
changed // if these differ there is an error in the data.
explain how two or more computers connected to the Internet can have the same IP address and still communicate with each other
- the computers have private IP addresses
- so NAT will be performed
- so that the computers can communicate on the internet
reasons why IPv6 has been introduced to replace IPv4
- There are not enough (unique) addresses in IPv4
- Eliminate need for NAT / network address translation
- more efficient routing is possible;
- Improved facilities for multicasting;
- Automatic configuration possible without DHCP;
- Allows bigger packet sizes;
