Chapter 7 Flashcards
What does the network layer do?
It routers packets from source node to destination node.
What is the primary example of a network layer protocol?
IP (Internet Protocol)
What are layer 3 packets known as?
Datagrams
How does a IP routing algorithm work?
1: check if A and B is on the same network. If yes deliver directly
2: Consult routing table. If entry exists, forward to next hop
3: If there isnt an entry in routing table, Send to A’s default gateway
4: If there is no default gateway, discard
Is IP reliable or unreliable?
Unreliable
What does TTL refer to on layer 3 with IP?
Max amount of hops a packet may still take before being discarded.
What makes IP unreliable?
Easily discard packets, Checksum only covers header ( wont detect changes in data)
When is a packet discarded with IP?
When TTL becomes 0
What does a IPv4 header have?
Version, TTL, Protocol, Header checksum, Source address, Destination address, Total Length, Fragment Offset
How many bits is in a IPv4 address?
32 bits
What are the different classes and their leading bits in IPv4?
A = 0 is the initial BIT. Initial BYTE identifies the network. Remaining 3 BYTES identifies the host
B = 10 is the initial bits. 2 initial Bytes identify the network, remaining 2 identifies the host
C = 110 is the initial bits. 3 bytes identifies the network, and one the host.
D = 1110 is the initial bits, used for multicast addressing.
E = 1111 unused
How do you identify a network?
Make all of the host portion of the network 0’s
10.0.0.0
How do you get the broadcast address?
Make the host portion all 1’s
10.255.255.255
How many hosts can you have on a single network?
2^n - 2 ( -2 because of network identifier + broadcast address)
n = bit in network field
How do you work out how many networks there can be in a single class?
2^(n-i)
n = number of network bits
i = number of initial bits (since we are going by class)
What does a netmask indicate?
Which bits in an address form the network and which part forms the host
What does a netmask consist of?
All 1’s in the network portion
What does the netmask look like for each class?
A = 255.0.0.0
B = 255.255.0.0
C = 255.255.255.0
What does CIDR do and what is it know as?
Classless Inter-domain Routing
Notes the number of bits that form the network portion
10.0.0.0/8 = leftmost 8 bits is the network portion. remaining 24 = host portion
What is subnetting?
Divide the network into subnetworks.
Example of sub netting?
10.1.0.0 is used for sales. 10.2.0.0 is used for production
Does the split between host portions and network portions occur only on byte boundaries?
No.
Make a class C address netmask but use 4 bits to identify the host and 4 to identify the subnet
11111111.11111111.11111111(all of this is for class C so far).1111(4 bits for subnet) 1111(4 bits for host)
netmask = 11111111.11111111.11111111.11110000
How do you get the network address on which a host is located?
Do a logical AND of the address and the netmask
Example of getting the network address on which a host is located
IP address of host = 192.168.1.100
subnet mask = 11111111.11111111.11111111.11110000
IP address of host = 192.168.1.100 aka 11000000.10101000.00000001.01100100
subnet mask = 11111111.11111111.11111111.11110000
Network address=
11000000.10101000.00000001.01100000
aka 192.168.1.96
Thus network address of the host 192.168.1.100 is 192.168.1.96
What is supernetting?
Combining network addresses to form a bigger network
Why is supernetting needed?
To speed up routing
How does IPv4 routing work?
1: If A&M = R&M (A = address, M = Mask, R = router) Send directly via data link layer. (If they are on the same network send via data link layer)
2: If there exists a triplet (Nj, Mj, Hj) (N = network, M = mask for that network, H = Address of next hop) send the packet to Hj. ( If there is a entry in the routing tab send it to H (on the same local network)
3: If no entries in Routing table send to default gateway. Deliver directly with default gateway if possible
4: if no default gateway discard it
Does IP allow a route to be specified?
Yes aka source routing
What is the difference between strict and loose source routing?
Strict = exact route is specified
Loose = Hops in source route are merely nodes that should be visited along the way
Routing algorithm steps:
1: has the datagram reached it destination?
2: Check if the destination is directly connected to current router ( if yes use layer 2 to deliver)
3: Determine next hop that may be reachable (RIP /OSPF)
A router is sometimes referred to as a …….
Multi-homed host
What does arp stand for?
Address Resolution Protocol
What are the most common way to clearly identify networks?
CIDR notation or network address + netmask
What is PPPoE and what does it do?
Point to point protocol over ethernet
It creates a virtual link between the customer and the ISP
What is another name for wireless LAN?
Wifi
What is PDU and what does it do?
Packet data unit.
It places a restriction on the size of data it is able to carry by layer 2.
What is the Max PDU size of Ethernet?
1500 octets
What do you call it when the PDU is larger than the max PDU of layer 2?
Fragmentation.
Split IP datagram into smaller parts
How do you know if a IP datagram is fragmented?
It is indicated by the Fragment Offset field in each fragment’s IP header
If a IP datagram is fragmented how do you identify which part the fragment belongs to?
By viewing the Identification field (all fragments will use the same number that the original datagram used)
What does the Do not fragment flag indicate?
That a datagram should never be fragmented
What are the 5 RIRs (Regional Internet Registries)?
AfriNIC
ARIN
APNIC
LACNIC
RIPE NCC
What do RIRs do?
Manage the allocation and registration of IP addresses
What is the general purpose of ICMP?
Send control + status messages
What does ICMP stand for?
Internet Control Message Protocol
What do ICMP packets consist of and how are they “transported”?
A number and maybe a payload.
They are sent as the payload of a IP packet
Which command is the primary tool in network troubleshooters?
the ping command
How can you see which route is being used to any destination?
By using the traceroute command (or tracert on Windows)
What is ARP and what is it used for?
Address Resolution Protocol.
Used to determine the layer 2 address of a node, given its IP address
What are layer 2 addresses called?
MAC addresses (Media Access Control)
What is unicasting?
A one-to-one communication method.
What is multicasting?
Send a message to a specific group of devices
What is broadcasting?
Sending a message to all the nodes on a network
Difference between multicasting and broadcasting?
With multicasting the nodes that are not interesting will just ignore
What is IGMP and what does it do?
Internet Group Management Protocol.
Enables hosts and routers to communicate and establish which hosts are interested in receiving multicast traffic
What is NAT?
Network address translation
What does a NAT router do?
Receives outgoing traffic.
Forwards request to node on the outside.
What is the problem with NAT?
Remembering which internal nodes sent what to what external nodes
When is a ingress router used?
When traffic enters a network
When is a egress router used?
When traffic leaves a network
How does the IPv6 header differ from IPv4?
TTL is replaced by Hop limit but still does the same thing
The Version field changed from 4 to 6
And it has payload length
How many bits is used in IPv6?
128
How does IPv6 separate the numbers and what is suppression??
Separated with a :
Suppressions = 2011:0000:0000:0000:0123 to
2011::0123 or 2011::123 (no leading 0s in hex numbers)
What is the routing prefix in IPv6?
Similar to the network portion in IPv4
What is the Interface identifier in IPv6?
Similar to IPv4 host number
Difference between MAC addresses and IPv6?
IPv6 has a intended scope.
Leading 0’s are not supressed MAC
What is anycasting in IPv6?
Send a message to any of a group of nodes
(a group within a group?)
How is multicast addresses differentiated?
By the special prefix ff00::/8
(It is a class D)
What is the loopback address in IPv6? (127.0.0.1 in IPv4)
::1/128
What address does a device use that doesnt have a address yet?
::0/128
Which prefix is reserved for site-local addresses in IPv6?
fc00::/7
What prefix is reserved for Unique local addresses?
fd00::/8
If IPv4 can address 16 unique hosts, how many number of networks can IPv6 Address and how many hosts per network?
16 = 2^4 thus 4 bits
Number of networks = (2*4)^2
and the same for hosts
What is used to assign addresses to individual interfaces
DHCP
By who is routable IPv6 prefixes assigned?
IANA
Who manages routable prefixes?
RIRs
What is tunnelling?
Encapsulating one protocol’s packet as the payload of another protocol
What is ATM?
Asynchronous Transfer Mode. Layer 1-3.
Usually used by telecommunications providers
How many bytes is in A ATM packet and what is it made up of?
53 bytes
5 bytes = header
48 bytes = payload
When is ATM path determined?
Before data transmission starts
