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Komtek > Modules 8-10 Communicating Between Networks > Flashcards

Modules 8-10 Communicating Between Networks Flashcards

1
Q

What is the network layer? What are its basic operations?

A

The network layer is the 3rd layer in the OSI model. It is

about communication between source and destination.

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2
Q

Why was NAT made? Positives and negatives?

A

Because there is not much left from the Ipv4 address space Nat was created to extend the IPv4 address space at the cost of losing direct communication and public IP addressing.
This resulted in increased network complexity because NAT was originally meant as a temporary solution, but it now it creates issues with header manipulation and causing additional latency.

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3
Q

What is the Ipv4 packet header? What are its limitations?

A

It tells us the most import info about the packet (e.g src/dst IP address) in binary.

Ipv4 address depletion: not much left from Ipv4 address space

Lack of end-to-end connectivity: Private addressing & NAT was created to extend the IPv4 address space at the cost of losing direct communication and public IP addressing.

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4
Q

What is classful addressing?

A

Old addresses came in blocks of fixed size (A,B,C)
Carries size as part of the address; inflexible!
E.g class B allocated address has 65K hosts even though new might have 2K hosts only.

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5
Q

What is sub-netting

A

Splits up IP prefix to help with management of network - known to local routers but looks like a single prefix from outside.

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6
Q

What is classless InterDomain Routing (CIDR)?

A

It is a more efficient use of Ipv4 address space than classful method, this is because the network portion can be of arbitrrary length; within the allocated portion of ISP’s address space.

The usual method we use today to split up IP addresses and route them.

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7
Q

What is Network Address Translation (NAT), and what are its characteristics?

A

NAT allows an organization to use a smaller number of public IP addresses with the use of private IP addresses.

Uses TCP/UDP port to tell connections apart

Violates layering: very common in homes

With special config, servers cannot be behind a NAT since clients don’t know the server’s local address to establish a connection

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8
Q

What is Ipv6 and why was it made?

A

Ipv6 is a better version of Ipv4, it was made to overcome the limitations of Ipv4.

It has:

Increased address space: Ipv4 has 4 billion, Ipv6 has 340 trillion.

Improved packet handling: Simpler headers with fewer field! 40 bytes long.

Eliminates the need of NAT’s , everyone gets Ipv6 address.

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9
Q

What does the Ipv6 packet header do?

A

It may contain extension headers (EH)
Provide optional network layer info
Placed between Ipv6 header and payload
May be used for fragmentation, security, mobility support, etc

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10
Q

Where can a host send packets to?

A

A host can send packets to

Own 127.0.0.1 Ipv4 ::1 Ipv6
Local: dst on the same LAN
Remote dst on a different LAN

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11
Q

What determines if a host is local or remote?

A

The source

Ipv4: Source uses its own ip address and subnet mask, along with the destination IP address.
IPv6: Source uses network address and prefix advertised by the local router.

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12
Q

What is the default gateway (DGW)? What is it properties?

A

A default gateway is the node in a computer network that serves as the forwarding host to other networks when no other route specification matches the destination IP address of a packet.

Same ip address as the rest of the LAN
Can route to other networks
Either set statically by the host or determined through DHCP protocol in IPv4
Ipv6 uses either router solicitation (RS) or manual config

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13
Q

What are the three routing types we have?

A

Directly Connected
Remote
Default route

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14
Q

What is Directly connected routing?

A

Automatically added by the router, an active interface with an address.

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15
Q

what is Remote routing?

A

Router does no have a direct connection and may be learned in 2 ways

Manually: with a static route,

  • Must be adjusted manually by net admin when there’s a change in topo
  • Good for small networks.

Dynamically: Using a routing protocol

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16
Q

what is Default route?

A

Forwards all traffic to a
specific direction if no match in routing
table

17
Q

What is dynamic routing?

A

A dynamic routing protocol allows the routers to automatically learn about remote networks, including a default route, from other routers. Routers that use dynamic routing protocols automatically share routing information with other routers and compensate for any topology changes without involving the network administrator.

18
Q

What are the two types of addressing on (Ethernet) LAN?

A

L2 Physical address (MAC addr) NIC to NIC communication of frames on same LAN

L3 Logical Address (IP address) communication from src to st (end-to-end, multiple networks)

19
Q

Which messages do Neighbour Discovery use to function?

A

Neighbour Solicitation(NS) and Neighbour Advertisement

  • Device-to-device messaging such as address resolution
  • NS is multicast

Router Solicitation (RS) and Router Advertisement (RA)

  • Used for messaging between devices and routers for router discovery (finding an ipv6 router)
  • used for dynamic address allocation and stateless address autoconfiguration
  • SLAAC devices send the router a request for the network prefix, and the device uses the perfix and its own MAC address to create an IP address.

Redirect messages are used by routers for better next-hop selection.

20
Q

Where is the Ip address and MAC address if they are on the same device?

A

On the same network, destination Ip address and dewstination MAC address belong to same device.

21
Q

What happends if the destination IP address is on a remote net?

A

If dst IP address is on remote net, dst MAC address will be set to DGW’s MAC addr.

22
Q

What is Address Resolution Protocol (ARP)? What is its basic functions?

A

ARP is used on devices to resolve IPV4 address into MAC address and determine the destination of a local device, then maintaing an ARP table of the IPv4 to MAC address mapping.

23
Q

How do you send a frame using ARP?

A

a) If destination is on the same net, search ARP table for a destination Ipv4 and a MAC address match.
b) If dst is on a different net, search ARP table for Default Gateway s IPv4 address
c) If found, corresponding MAC address wil be used as dst MAC address in the frame.
d) If not found, send an ARP request.

24
Q

What is an ARP request?

A

An ARP request is sent when a device needs to determine the MAC address that is associated with an IPv4 address, and it does not have an entry for the IPv4 address in its ARP table.

Broadcast frame (FF-FF-FF-FF-FF-FF as dst MAC addr), propagated through and 
processed by switches on all interfaces except incoming! If no ARP reply received, 
packet is dropped!
25
Q

What is an ARP reply?

A

Unicast meaning dst MAC address is the sender of ARP request; also, with
0x806 as EtherType;

26
Q

What is an ARP table? Are the entries permanent and can they be removed?

A

An ARP database for maintaing IPv4 to MAC address mapping in the network.

Entries are not permanent and are removed an ARP cache timer expires8 if no frame is received from a device for a certain duration!

Timer duration is OS dependent
ARP entries can also be removed manually.

27
Q

What does the Ipv6 neighbour disvovery provide?

A

Address resolution (discovering the MAC address destination associated with given IP address)

Router discovery

Redirection Services

28
Q

Where does the Neighbour Discovery Protocol store its Ipv6 to MAc address mappings?

A

A neighbour cache

29
Q

What is addressing end devices?

A

End devices must be configured with a unique IP address for identification on the network.

30
Q

What is encapsulation?

A

The network layer encapsulates the protocol data unit(PDU) from the transport layer into a packet.

The process adds IP header information, such as source IP address and destination IP address.

The encapsulation process is performed by the source of the IP packet.

31
Q

What is routing?

A

The netowork layer provides services to direct the packets to a destination host on another network. To travel to other networks, the packet must be processed by a router.

The role of the router is to select the best path and direct packets toward the destination host in a process known as routing. A packet may cross many routers before reaching the destination host. Each router a packet crosses to reach the destination host is called a hop.

32
Q

What is de-encapsulation?

A

When the packet arrives at the network layer of the destination host, the host checks the IP header of the packet.
If the destination IP address within the header matches its own Ip address, the IP header is removed from the packet.

After the packet is de-encapsulated by the network layer, the resulting layer 4 PDU is passed up to the appropriate service at the transport layer.

The de-encapsulation process is performed by the destination host of the IP packet.

33
Q

What does the Ipv6 packet header contain?

A

Version, Traffic class, flow label, payload length, next header, hop limit, source and destination

Komtek (10 decks)

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