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8 computers & security 110 (2021) 102423
trol over the complete network. The centralized controller
maintains the complete picture of the network so it can exam-
ine the network trafc in a better way as compared to tradi-
tional network ( Salman et al., 2016 ). Some of the popular SDN
controllers ( Shalimov et al., 2013 ) include NOX ( Gude et al.,
2008 ), POX ( Kaur et al., 2014 ), Ryu ( Shalimov et al., 2013 ), Bea-
con ( Erickson, 2013 ), Opendaylight ( Khattak et al., 2014 ), Flood-
light ( Bholebawa and Dalal, 2018 ), ONIX ( Koponen et al., 2010 ),
ONOS ( Berde et al., 2014a ).
3.1.3. Application plane
In the SDN Architecture, application plane comprises multi-
ple applications like load balancer, rewall, trafc monitoring,
and others that are running on the controller. These applica-
tions dene the functionality of the forwarding device. In this
way, the SDN utilizes the network infrastructure in a better
way than the traditional network. In SDN, the same device can
perform different functionalities, but in the conventional net-
work, each device performs dedicated functionality due to its
rigid architecture.
3.1.4. Southbound API
SDN separates the control functionality from the forwarding
hardware and the southbound interface is needed to provide
communication between these two planes. There are various
southbound APIs available like ForCES ( Haleplidis et al., 2015 ),
OpenFlow ( McKeown et al., 2008 ), Netconf ( Denazis et al.,
2015 ). The OpenFlow is the standard southbound interface de-
ned by the Open Network Foundation (ONF). For secure com-
munication through the southbound interface, transport layer
security is implemented on OpenFlow protocol, but this is
not mandatory as recommended by the ONF ( Agborubere and
Sanchez-Velazquez, 2018 ).
3.1.5. Northbound API
Applications in the management plane interact with the con-
troller through the northbound API. There are various types
of northbound APIs such as REST API ( Zhou et al., 2014 ), Fren-
tic ( Foster et al., 2010 ), Pyretic ( Reich et al., 2013 ), Procera
( Voellmy et al., 2012 ), Netcore ( He et al., 2017 ). The standard-
ization of the northbound interface is still a topic of discussion
due to its dynamic nature.
3.2. Vulnerable points in the SDN architecture
The SDN makes the management of networks easier by con-
trolling the network behavior from a single point. The overall
expenses of the network are reduced by using vendor agnos-
tic network operating system instead of using vendor-specic
tightly coupled hardware devices. In spite of the advantages
of the SDN, it comes up with some limitations. The security
of SDN has become a signicant concern among the research
community and industry ( Chica et al., 2020; Tus h ar Ubale,
2019 ). The various target points of attacks in SDN architecture
are shown in Fig. 5 ( ROCHAK SWAMI, MAYANK DAVE, 2019 ).
Moreover, the authors identied vulnerabilities at all the tar-
get points as depicted in Fig. 5 ; these weaknesses are exploited
by the attacker to launch various kinds of attacks on SDN ar-
chitecture. Table 5 shows the various security threats associ-
ated with different SDN layers.
(i) Data plane switches : Data plane consists of dumb Open-
Flow enabled switches that make it vulnerable to sev-
eral security threats like ow table modication, topol-
ogy spoong, and DDoS attack ( Gao et al., 2018b ). In the
ow table modication attack, a malicious node inserts
or modies the ow table rules to sniff ongoing com-
munication happening in a network or to perform Man-
in-the-middle Attack (MITM), resulting in loss of data
integrity. The purpose of topology spoong attack is to
create a fake network view for the controller to redi-
rect the trafc to the attackers machine. Moreover, the
limited memory and processing constraints in the SDN
switches make it vulnerable to ow table overloading
and buffer saturation attack ( Durner et al., 2017 ).
(ii) Southbound interface : The Openow is a popular south-
bound protocol. However, it does not impose the se-
cure connection between OpenFlow switch and con-
troller because TLS level security is recommended but
not mandatory. The lack of TLS security will open the
door for attackers because when the controller inserts
rules into the OpenFlow switch through the south-
bound interface, these rules can be easily intercepted by
the attacker ( Agborubere and Sanchez-Velazquez, 2018 ).
Therefore, an attacker can modify existing ow rules or
add malicious ow entries to misdirect packets, which
can have devastating effects on the entire network.
Moreover, the limited bandwidth capacity of communi-
cation channel makes it vulnerable to bandwidth satu-
ration attack. To exhaust the bandwidth of communi-
cation channel, a malicious node crafts the values of
packet header elds so that these packets are not able to
match with the existing ow rules and switch is forced
to send these packets to the controller, resulting in con-
gestion on the communication channel.
(iii) SDN controller : It becomes the main target of attack-
ers as it controls the whole network. If the attacker
impersonates the controller or modies its function-
ality in some way, then it can destroy the entire net-
work. A hijacked controller can perform various attacks
such as blackhole, fake ow rule insertion, and DDoS
attack. A malicious controller can insert fake ow rules
to change the route of the packets, resulting in losing
data integrity and condentially of sensitive informa-
tion. In the SDN architecture, a switch sends every new
packet of a ow to the controller. An attacker exploits
this property of SDN to exhaust the computational and
network resources of the control plane by generating
a huge amount of fake new packets ( Han et al., 2019;
Wang et al., 2017 ).
(iv) Northbound interface : The applications use the north-
bound interface to collect the network statistics or to
give instructions to the controller for managing the net-
work. Due to the lack of standardization, this interface
is susceptible to multiple security threats such as tam-
pering, DoS, and eavesdropping ( Laan, 2015 ).
(v) Applications plane : In the SDN framework, forwarding de-
vices are dumb devices and behave according to the pro-
gram running on the controller. Due to the lack of au-
thentication and access control mechanism, this plane
is susceptible to multiple security threats like malicious