Understanding Network Topology and Routing Protocols

This article explains the basics of network topology, ARP table mapping, and routing protocols. It also covers the stop and wait protocol for data transmission. The content is relevant to SIT202: Computer Networks Trimester 2, 2018.

SIT202: COMPUTER NETWORKS TRISEMISTER 2, 2018
Name:
Subject:
Course Unit

QUESTION 1:
On this sample topology there are 6 hosts each having a unique ip address, 2 switches and a
router that connects to the internet then to the remote server. To demonstrate how both switches
and routers cross this network will look at the table which they maintain. ARP Table mapping of
ip address to Mac address, Mac Address Table which maps switches to the mac address. As
traffic goes through the switch, devices that are connected to each port by Mac Address are
identified and are recorded by the Mac Address table. Routing Table maps the ip network to
interfaces.
PC-1 has the data that needs to be conveyed across the network and to the destination that is the
remote server. It also has the ip address of the remote server so PC-1 creates an L3 header that
basically consists a few pieces of information (Doeppner, 2010). Mainly, Source ip address
(SRC) and Destination ip address that is 192.168.10.8/24 and destination ip address (DST) which
in this case is the remote server. PC-1 then compares the destination ip address on its own
network to determine that it’s a full network. PC-1 will then create a layer 2 to take the packet to
the router and since it doesn’t have the mac address it will need to use the ARP to discover its
default gateway’s Mac address. The host then sends the ARP request 192.168.10.0/24 to the
router. ARP request is a frame that literally asks if the ip address is there then sends to the mac
address. First of all the switch will basically learn the address and broadcast the ARP request to
the entire network and both the router and the Human Resource pc will receive the request and
since the Human Resource Machine doesn’t have the response to the request it will discard it.
The router on the other hand generates the response. The switch receives the response and
automatically learns the mac address of the respondent which was received on one of the port
that was connected to the router then forward the response to the host which in this case is PC-1
(Jimmei, 2008). This entire time the data is held by the host while waiting for the address
resolution to be processed to complete.
Since PC-1 has the Mac Address it can finally sends data to the remote server. The host creates
an L2 header that sends the packet. L2 is made up of the source and destination address of the
router. L3 contains Source ip address and the destination ip address of the remote server. L3’s
main work is to send data from the sender to the receiver while L2 basically gets the data from

hop to hop within the network. The frame arrives on the switch which already has the entry Mac
address table on that port. The switch then forwards the frame to the Ethernet connected to the
router. On the other end the router receives the frame then withdraws the L2. The frame consist
of the data, L3 and L2 and since L2 basically consists of hops from the PC-1 to the router, it’s
withdrawn. The router then looks at the destination which in this case is the remote server that is
connected to the internet (Kerman, 2014).
In this part the router then determines the dynamic routing protocol that is going to use to convey
the frame. Routing protocol determines the best path to each network, which is then added to the
routing table which is one of the primary table. This trade enables switches to consequently find
out about new systems and furthermore to discover interchange ways if there is interface
inability to the present system. Contrasted with static steering, dynamic directing requires less
managerial overhead. For this situation there two kinds of dynamic steering convention that is,
Distance Vector Routing protocol and Link State Routing Protocol. Distance Vector Routing
Protocol routes are advertised as vectors of distance and direction. It is determined by the
number of hop counts and direction to the next hop router and exit interface. It basically uses a
signpost to the next router. Link-State Routing Protocol on the other hand creates a complete
view of the network by gathering information from all other routers. In contrast to distance
vector, this determines the connectivity of the network and does not utilize intermittent updates
of their routing information data to the neighbors. Since the frame needs to reach to the
destination and we basically don’t know which geographical area the server is located. The
router will be promoted to use the link state routing protocol which is determined by the strength
of the connectivity of the network.
Router will send an ARP response which will be broadcasted to request for the mac address of
the remote server (Ooka, 2013). On the other end, the request is received through the entire
network and since it is the stitch, it is connected to the remote server then it generates a response.
The router then attains the mac address and since it already has the ip address of the remote
server then the frame is received and before the withdrawal of the data, L3 is first eliminated
since it has confirmed the destination ip address. And now since it has received the data the
server has to respond to pc-1 that the data sent has been received. The whole process then is done
for the response.

Network
destination
Net mask Gateway Interface Metric
192.168.10.7 255.255.255.0 192.168.10.1 209.165.200.226 10
Source address: 192.168.10.7/24
Destination address: 209.165.200.226/27

QUESTION 2:
Ip Routing or frame forwarding is based on the protocol used to determine the best path in which
the packet can follow in order to be transmitted across multiple network from its source to
destination. In this case the PC-A which is regarded as the host mainly generates a frame that
consists of layers one and two and the data itself .
Since PC-B is directly connected to a software utility known as ping then it does not differs the
transport protocol to exchange data between the networks. It is well known as the message
protocol used for the ping command. PC-B ping command sends an ICMP echo request to the
largest host that is PC-A. PC-A then replies with an echo request to the target PC-B. In both
movement it consists of three ip headers. Upper layer to which the payload is delivered i.e.
ICMP, UDP, TCP, Source IP address, and destination ip address.
PC-A puts destination address in the packet header and then releases it to the router. The router
looks up for the destination in the routing table then sends the packet to the next hop towards the
destination. Upon addressing of the network to determine whether the host is a local or remote
destination the ICMP uses the host router to communicate network level information such as
error reporting: unreachable hos, network, port, and protocol, Echo requesting/ reply (used by
ping).PC-A sends a series of UDP packets to PC-B . The first three of the packets have TTL set
to 1, 3 secs apart and 3 packets have TLL set to 2. Then the packets are sent to unused port
number. When packet expires, the router eventually discard the packet and send to source an
error ICMP message (type 1, code 0). When ICMP error message arrives back to the host, PC-A.
PC-A calculates the round trip time. UDP eventually arrives to the correct intended host.
Destination returns at ICMP destination port echo reply (ping) then the packet is sent
QUESTION 3:
1.
 Distance Vector Routing Protocol.
 Link-state Routing Protocol

2.
 Distance Vector Routing Protocol
3.
 Distance Vector Routing Protocol routes are advertised as vectors of distance and
direction. It is determined by the number of hopes counts and direction to the next hop
router and exit interface. It basically uses as a signpost to the next router .
 Link-State Routing Protocol on the other hand creates a complete view of the network by
gathering information from all other routers. In contrast to distance vector, this
determines on the connectivity of the network and does not use periodic updates of their
routing information to the neighbors.
 Distance Vectors will not work because the type of network being used here is a WAN
and both router are in different geographical area which makes them hard to
communicate due to the distance and the direction (Abolhasan, 2014).
4.
 172.16.10.1/24
QUESTION 4:
The flowchart basically explains how both the sender and the receiver of the application layer
use the stop and wait protocol to send data. Frame consists of Layer 2 and layer 3. Layer 2
consist of the number of hops that the frame will take on reaching the router and layer 3 consist
of Source ip address including destination ip address. But in this the communication is conveyed
across the same given layer.
To commence the process, first the sender requests the process of sending before starting,
generates and dispatches one data packet at a time. On the receiving end the receiver consumes
the packet flows the control and after the consumption it sends an acknowledgment to the sender.
The sender receives the acknowledgement the stops the entire process. In this step, the packet
was set to a given sequence number that was 010101 in that on the sending of the packet it
emulated as 0. And upon the consumption it changed to 1 and gave back the response as 1.

The sender then request the process then transmit. In this the data is lost. Then the receiver takes
time out. At every given time out, retransmission of data resolve to loss of data problems.
Loss data loss data loss data
Stop (and) wait + Time out + sequence (Data) + sequence (ACK)
No
Yes
Start
Generate
Frame (Req)
Packet arrival and
ready for dispatch
If sender
start Req?
Receiver Generate
acknowledgement response
Stop
Packet is lost

d.
The sender the requests the process. On the sequence number it’s represented as 0. The request
starts then is received by the receiver it consumes the packet then sends the acknowledgement
but in this it is lost on the way. The senders tend to wait then resend the packet. The receiver
sends ACK instead of negative because of sequence number attached to sender packet. But this is
resolved by introducing sequence number of acknowledgment also (Ha, 2013).
In outline, the sender sends information casing or bundle with succession number of 0.
Beneficiary, in the wake of accepting information outline, sends affirmation with grouping
number 1 that is for the following expected information outline. There is just a single piece
succession number that suggests that both sender and recipient have buffer for one edge or parcel
as it were.

References
Abolhasan, M., Wysocki, T. and Dutkiewicz, E., 2014. A review of routing protocols for mobile
ad hoc networks. Ad hoc networks, 2(1), pp.1-22.
Doeppner, T.W., Klein, P.N. and Koyfman, A., 2010, November. Using router stamping to
identify the source of IP packets. In Proceedings of the 7th ACM conference on Computer and
communications security (pp. 184-189). ACM.
Ha, S., Han, S.W., Kim, T.E., Bharghavan, V., Madhow, U. and Ramchandran, K., Bytemobile
Inc, 2013. Data transport acceleration and management within a network communication
system. U.S. Patent 7,099,273.
Jimmei, T., Toshiba Corp, 2008. Communication system, router, method of communication,
method of routing, and computer program product. U.S. Patent 7,436,833.
Kermani, P. and Kleinrock, L., 2014. Virtual cut-through: A new computer communication
switching technique.
Ooka, A., Ata, S., Koide, T., Shimonishi, H. and Murata, M., 2013, July. OpenFlow-based
content-centric networking architecture and router implementation. In Future Network and
Mobile Summit (FutureNetworkSummit), 2013 (pp. 1-10). IEEE.