Quiz 4 Network Layer

CNT 3004 - Computer Networks and Communication

Network Layer (Layer 3)

Implemented in….

• laptop with wired connection

• linux server with wired ethernet connection

• mobile w/ wireless wi-fi connection

• cisco edge router

Control Plane

• Monitoring and managing the
  configuration and performance of an
  network device

• The routing algorithm function in one router communicates with the routing algorithm function in other routers

• Router executing the routing protocols, responding to attached links that go up or down

• Router communicating with the remote controller (in the SDN case) and performing management functions

Data Plane

• Looking up address bits in an arriving datagram header in the forwarding table

• Moving an arriving datagram from a
  router’s input port to output port

• Packet queuing on router input ports

Router Architecture

Dynamic Host Configuration Protocol (DHCP)

• New client sends Discover message within a UDP packet to port 67 at IP 255.255.255.255 via Link Layer to all nodes on subnet

• DHCP server responds with Offer message to the client with a DHCP offer message that is broadcast to all nodes on the subnet, using the IP broadcast address of 255.255.255.255

  • Message contains the transaction ID of the received discover message, the proposed IP address for the client, the network mask, and an IP address lease time

• New client responds with Request message confirming config para

• Server responds with a DHCP ACK message, confirming the requested parameters

Consider the three subnets in the diagram. What is the maximum # of interfaces in the 223.1.2/24 network? What is the maximum # of interfaces in the 223.1.3/29 network?

/24 → 32 - 24 network bits = 8 host bits

2⁸ = 256 interfaces

/29 → 32 - 29 network bits = 3 host bits

2³ = 8 interfaces

NAT (network address translation)

• all devices in local network share just one IPv4 address as far as outside world is concerned Network Layer: 4-55

• all devices in local network have 32-bit addresses in a “private” IP address space (10/8, 172.16/12, 192.168/16 prefixes) that can only
  be used in local network

• outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #)

  • remote clients/servers will respond using (NAT IP address, new port #) as destination address

• remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair

• incoming datagrams: replace (NAT IP address, new port #) in destination fields of every incoming datagram with corresponding
  (source IP address, port #) stored in NAT table

Identify how many hosts are available. What is the network address, broadcast, host min, and host max for the IP address, 172.19.0.22/26?

/26 → 32 - 26 network bits = 6 host bits

Available hosts = 2ⁿ - 2 = 2⁶ - 2 = 64 - 2 = 62

Cider to Netmask: subnet mask /26 in binary → 11111111.11111111.11111111.11000000 = 255.255.255.192

172.19.0.22 in binary → 10101100.00010011.00000000.00010110

Perform the AND operation between subnet mask and network address: 10101100.00010011.00000000.00000000 = 172.19.0.0

Network Address: 172.19.0.0/26

Broadcast: 172.19.0.63

Host Min: 172.19.0.1

Host Max: 172.19.0.62