=Paper=
{{Paper
|id=Vol-2522/paper11
|storemode=property
|title=Simulating of Fault-Tolerant Gateway Based on VRRP Protocol in OMNeT++ Environment
|pdfUrl=https://ceur-ws.org/Vol-2522/paper11.pdf
|volume=Vol-2522
|authors=Ilya I. Noskov,Vladimir A. Bogatyrev
}}
==Simulating of Fault-Tolerant Gateway Based on VRRP Protocol in OMNeT++ Environment==
https://ceur-ws.org/Vol-2522/paper11.pdf
111
Simulating of Fault-Tolerant Gateway Based on VRRP
Protocol in OMNeT++ Environment*
Ilya I. Noskov1[0000-0002-5489-4092] and Vladimir A. Bogatyrev1[0000-0003-0213-0223]
1 Saint-Petersburg National Research University of Information Technologies, Mechanics and
Optics, Kronverksky prospect, 49, Saint Petersburg, 197101, Russian Federation
noskovii@mail.ru
Abstract. Ways of improving the fault-tolerance of local computer network
gateways using the Virtual Router Redundancy Protocol (VRRP) are considered.
VRRP protocol is analyzed in the OMNeT++ simulation environment that has
models of real communication channels and TCP/IP network protocols. The
method of constructing computer network models with a fault-tolerant gateway
based on the VRRP protocol in the OMNeT++ environment is proposed in the
paper. The paper provides a description of all the main stages of creating and
carrying out experiments with a computer network model. All windows of the
simulation environment in which the model is parameterized and settings are
considered in detail. The paper also describes the internal language of the OM-
NeT++ environment for the development of computer network models - NED.
The process of creating scripts that allow simulating various events in the simu-
lation process, such as the break of the communication channel between devices
or the failure of the device is considered in detail. ANSA-INET is the OMNeT++
framework, which contains many modules and implementations of network pro-
tocols, including the FHRP family of protocols. This framework is used as the
main framework for developing models in this paper. Capabilities of this frame-
work are shown while simulating the VRRP protocol for creating a fault-tolerant
gateway in the local area network.
Keywords: Simulating, Fault-Tolerant Gateway, Computer Networks, VRRP,
OMNeT++.
1 Introduction
At present, the number of real-time systems with high requirements for functional and
structural reliability has significantly increased in conditions of destructive impacts on
the channel or active network equipment [1-4]. That is why reliability and fault-toler-
ance researching of information and communication systems and networks is carrying
out nowadays [5-6]. The choice of design solutions for the construction of information
and communication systems is based on analytical or simulation modeling [7-10].
* Copyright 2019 for this paper by its authors. Use permitted under Creative Commons License
Attribution 4.0 International (CC BY 4.0).
112
Gateway is an important element for traffic forwarding in local area computer net-
works because it links this network with others. Failure of this element can lead to the
inoperability of the entire subnet and the loss of large amounts of data. To ensure gate-
way reliability in local computer networks, it is necessary to use device redundancy and
using specialized gateway protocols for developing a cluster of routers.
For effective interaction of computer nodes of distributed systems, it is necessary to
build networks with a redundancy of elements of active network equipment, with the
support of multipath routing [11-14] with the possibility of choosing an alternative
route to the destination node for balancing traffic. The transport coding allows reducing
the average delays of messages in the network with the multipath coupling of nodes
[15–16]; the effect is achieved due to the coding that it is possible to recover the entire
message without repeating transmissions. In redundant real-time information and com-
munication systems, increasing the likelihood of timeliness and reducing the average
latency of servicing requests allows for redundant maintenance, which creates copies
of requests made by different nodes of the system or by different sequences of nodes
[17-19]. Redundant query service can be effectively applied in cluster architecture sys-
tems and in multipath data transmission systems that are sensitive to delays.
The aim of this work is building reliable fault-tolerant network solutions based on
the development of simulation models in the OMNeT++ environment, which allow us-
ing real communication tools and network protocols to ensure the fault-tolerant of gate-
ways [20-24].
2 Fault-tolerance of gateways
The fault-tolerance of computer networks at the network level is ensured by the reser-
vation of active network equipment and/or communication channels, as well as the use
of specialized protocols. There are a whole family of First Hop Redundancy Protocols
(FHRP) protocols that allow building fault-tolerant computer networks with redundant
switching nodes. This is achieved by combining several routers into one virtual router
that responds to ARP requests and distributes traffic to currently active router from the
entire cluster. If the active router fails, another router from the group assumes its role,
and the traffic actually continues through the other router. Thus, in a computer network,
reliability, and probability of delivery of packages to the destination node increase.
3 Virtual Router Redundancy Protocol
VRRP is a network protocol from the FHRP family designed to increase the availability
of routers acting as a default gateway. This is achieved by combining a group of routers
into one virtual router and assigning them a common IP address, which will be used as
the default gateway for computers on the network.
At any time, only one of the physical routers performs traffic routing, that is, it be-
comes the main VRRP router, the rest of the routers in the group become redundant. If
the main router becomes unavailable, then one of the backup ones assumes its role - the
one with the highest priority.
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The basic concepts of the VRRP protocol are:
VRRP Router — a router with running VRRP protocol. It can participate
in one or more virtual routers.
Virtual Router (VR) — is an abstract object managed by VRRP protocol.
Performs the role of the default router for computers in the network. A vir-
tual router is a group of router interfaces that are on the same network and
share a Virtual Router Identifier (VRID) and a virtual IP address.
IP Address Owner — VRRP router that uses the IP address assigned to the
virtual router as the real IP address assigned to the interface.
ADVERTISEMENT — messages that are sent by the Master-router.
Virtual IP address — is the IP address assigned to the interface of one of
the routers that make up the Virtual Router. Also known as Primary IP Ad-
dress. VRRP adverts always use the virtual IP address as the sender's ad-
dress.
VRRP Master router — is VRRP router that is responsible for sending
packets sent to an IP address that is associated with a virtual router and for
responding to ARP requests sent to this address. If the owner of the IP ad-
dress is available, then it always becomes the Master.
VRRP Backup router — is a group of routers that are in standby mode and
are ready to take on the role of the VRRP Master router as soon as the cur-
rent VRRP Master router becomes unavailable.
Virtual MAC address — is 0000: 5E00: 01xx, where xx is the number of
the VRRP group.
VRRP is designed to increase the availability of routers that use as a default gateway
in the local area network.
For a group of routers, they are configured to belong to a virtual router. In fact, a
virtual router is a group of router interfaces that are on the same network and share a
Virtual Router Identifier (VRID) and virtual IP address.
A VRRP router can be in multiple virtual routers, each with a unique VRID/IP ad-
dress combination. The correspondences between the VRID and the IP address must be
the same on all routers on the same network.
At any given time, only one of the physical routers performs traffic routing, that is,
it becomes a VRRP Master router, the rest of the routers in the group become a VRRP
Backup router. If the current VRRP Master router becomes unavailable, then one of the
VRRP Backup routers - the one with the highest priority - assumes its role. Setting
priority allows you to define more priority routers administratively.
The backup router will not attempt to intercept the role of the master router unless it
has a higher priority than the current master router. VRRP allows administrative block-
ing of the master-router role. The only exception to this rule is that the VRRP router
will always become the Master if it owns the IP address that is assigned to the virtual
router.
In each virtual router, only the master sends periodic VRRP messages to the reserved
group address 224.0.0.18. At the data link layer, the virtual MAC address is used as the
MAC address of the sender of VRRP announcements.
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For researching of this protocol, it is necessary to develop models for the simulation-
modeling environment, which will allow a detailed review of the operation of the pro-
tocol on various network configurations and topologies.
4 Develop a simulation model and carry out experiments
The specialized environment for computer network simulating OMNeT++ was chosen
for creating and researching simulation models of computer networks with fault-toler-
ant gateway because it is cross-platform, contains a large library of network compo-
nents and models of network protocols in different network layers, has a convenient
graphical interface and detailed English-language documentation.
OMNeT++ simulating environment is a cross-platform specialized environment for
simulating computer networks for various purposes. This program is written in C++
language and allows modifying its modules in this language, as well as building models
using a graphical editor or a specialized model description language. The simulation
results are available to the user in the form of tracing events or data arrays, from which
you can automatically build informative graphs and charts. Since this environment is
an open-source environment, the user has access to many different libraries and mod-
ules written by various developers and researchers. It has a great number of different
implementations of the vast majority of network protocols from the OSI stack. In addi-
tion, it has components of the VRRP protocol based on router models that support this
protocol.
The ANSA-INET library contains models of routers with the implementation of the
VRRP protocol for simulating computer networks with a fault-tolerant gateway. Fig. 1
shows the computer network model that was developed in the OMNeT++ environment:
Fig. 1. Model of a computer network
The OMNeT++ simulation environment allows you to build computer network models
not only using a graphical user interface but also with using specialized NED language.
This language has a C-like language and allows us to create models without using a
graphical environment. This can be useful when we build large networks consisting of
115
a big amount of different nodes. Fig. 2 shows an example of a network configuration
that was built via this language.
Fig. 2. NED fragment of the computer network model in the OMNeT++ environment
In this model, H1 and H2 nodes are clients. Clients send network traffic to each other.
SW1 and SW2 - switches. These switches connect subnets of H1 and H2 clients. R1,
R2, and R3 routers are a group of routers that have VRRP protocol to provide fault-
tolerance to the H1 client's subnet gateway. For working with the VRRP protocol, the
ANSA-INET framework provides a special type of the ANSA_VRRP_Router router.
In the model of this router, we can configure this protocol. The configuration of a clus-
ter of routers with VRRP protocols provides via using a special configuration file,
which is provided by the ANSA-INET library. Fig. 3 shows a fragment of the router's
configuration.
116
Fig. 3. Fragment of routers configuration
The configuration is an XML file that contains the settings of each of the interfaces of
the router. In this configuration, we can set their system name, address, description, and
other service information. Also in this file, we specify the VRRP settings for the correct
operation of the protocol: the virtual IP address of the fault-tolerant router, its id, and
description.
The UDP traffic generator is configured for the H1 client node. This generator cre-
ates a load flow towards the H2 client node. The UDPSink application is configured at
the H2 node. This application receives the traffic flow with the specified address and
destination port. In Fig. 4, we can see a fragment of the configuration of client applica-
tions.
117
Fig. 4. Simulating parameters and settings of UDP-applications
Also in this file, we set different parameters of routers using the path to the XML con-
figuration file and id of routers.
OMNeT++ simulation environment allows you to write scripts that can influence the
model process and simulate various events in the system. A script has been developed
for researching fault-tolerance in our computer network. This script simulates the break
of the communication channel between the SW1 switch and the R3 router. In Fig. 5,
we can see a fragment of developed in the OMNeT++ environment script.
Fig. 5. Fragment of scripts, which simulate the break of the communication channel between
the switch and active router
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Fig. 6 shows the simulation process before the break of the communication channel.
Fig. 6. Simulation before the break of the communication channel
Fig. 6 shows that the traffic from the client H1 goes through the router R3. At each
moment only one of the three routers sending traffic - the rest are in standby mode. The
script simulates the break of the communication channel between the SW1 switch and
the active router R3. Fig. 7 shows the simulation process after the break of the commu-
nication link.
Fig. 7. Simulation after a break of the communication channel.
Traffic from the H1 node is going through an R2 router since the R3 router is unavail-
able for H1 client. The VRRP algorithm allows us to change active router and traffic
from H1 client is sent via the R2 router. Thus, the computer network has the fault-
119
tolerant gateway that allows sending traffic after break communication links and/or
network equipment.
5 Conclusion
A computer network model has been developed with a fault-tolerant gateway based on
the VRRP protocol. The process of creating and researching computer network models
in the OMNeT++ environment is described in the paper. This approach allows building
computer network models using real communication tools and computer network pro-
tocols of the TCP/IP stack. The algorithm of the VRRP protocol for implementing fault-
tolerant gateway in the local area network is described and modeled in detail. The re-
sults obtained in this article may be useful to network engineers and designers when
building computer networks with a fault-tolerant gateway.
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