COMP3301/7308 Assignment 1 Generic Network Virtualization Encapsulation (Geneve) using Event Driven Programming solved

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1 Geneve: Generic Network Virtualization Encapsulation
This assignment asks you to write a simplified implementation of Geneve: Generic Network Virtualization
Encapsulation called gnveu. The implementation will support multiplexing multiple Ethernet tunnels over a
single UDP socket.
The purpose this assignment is to expose you to event driven programming, working against existing APIs
and libraries, and the use of the OpenBSD code style and tool chain.
This is an individual assignment. You should feel free to discuss aspects of C programming and the assignment
specification with fellow students. You should not actively help (or seek help from) other students with
the actual coding of your assignment solution. It is cheating to look at another student’s code and it is
cheating to allow your code to be seen or shared in printed or electronic form. You should note that all
submitted code will be subject to automated checks for plagiarism and collusion. If we detect plagiarism
or collusion, formal misconduct proceedings will be initiated against you. If you’re having trouble, seek
help from a member of the teaching staff. Don’t be tempted to copy another student’s code. You should
read and understand the statements on student misconduct in the course profile and on the school web-site:
2 Specifications
gnveu is used to tunnel multiple network connections over a single UDP connection. It supports tunnelling of
Ethernet (layer 2) packets inside the Geneve protocol.
Each network tunnel is connected to the kernel via the tap(4) device driver. Packets read from the kernel
are encapsulated in Geneve before being sent on the UDP socket. Geneve packets received from the socket
are decapsulated and written to the tap(4) device driver. The Geneve protocol will also be used to filter
Ethernet traffic.
2.1 Code Style
Your code is to be written according to OpenBSD’s style guide, as per the style(9) man page.
2.2 Compilation
Your code is to be built on an amd64 OpenBSD 6.5 system. It must compile as a result of running make(8) in
the root directory of your submitted assignment. Compilation must produce a binary called gnveu in either
the same directory, or in the obj directory if it exists.
Compilation of gnveu must succeed with -Wall passed as a flag to the compiler.
2.3 Invocation
When run with no arguments, or extra or unknown options, gnveu should print a usage message to stderr:
usage: gnveu [-46d] [-l address] [-p port] -t 120
-e /dev/tapX@vni
server [port]
and terminate with a non-zero exit code. Note VNI stands for Virtual Network Identifier.
gnveu takes the following command line arguments:
-4 Force gnveu to use IPv4 addresses only.
-6 Force gnveu to use IPv6 addresses only.
-d Do not daemonise. If this option is specified, gnveu will run in the foreground and log to stderr. By
default gnveu will daemonise.
-t idle_timeout (value specified in seconds) Close and exit after idle_timeout duration is exceeded. If
no traffic is received for a duration that exceeds the timeout, then the system is considered to be idle.
The duration must be a postive value specified in seconds. If no idle_timeout is given (or is invalid),
then an error message must be displayed. If a negative value is given, then no idle_timeout should
-l address (Optional and does not need to be used) Bind to the specified local address. By default
gnveu does not bind to a local address.
-p port (Optional and does not need to be used) Use the specified source port. By default gnveu
should use the destination port as the source port.
-e /dev/tapX@vni Tunnel enter/exit point for Ethernet (level 2) traffic for the specified tunnel device. The
@vni must be specified. Note VNI stands for Virtual Network Identifier per the draft-ietf-nvo3-geneve-16
specification. The VNI is used to filter the Ethernet traffic (depending on the payload type). When
either of the following VNI is specified, only ethernet packets containing the corresponding payload
type must be encapsulated and tunnelled. Other types of ethernet traffic should be filtered out and not
tunnelled. Hint: Version field in IPv4 and IPv6 packets.
VNI Traffic
4096 IPv4 only (filter out other types)
8192 IPv6 only (filter out other types)
Any not listed above Any Ethernet
server The address or host name of the remote tunnel endpoint.
port Use the specified port on the server as the remote tunnel endpoint. By default gnveu should use port
6081 as per the draft-ietf-nvo3-geneve-16 specification.
At least one tunnel must be configured.
If gnveu is unable to bind to the specified local address and port, connect to the remote server and port, or
open the specified tunnel interfaces, it should generate an appropriate error and terminate with a non-zero
exit status.
2.4 Functionality
• gnveu should use a single UDP socket to connect to the address specified by the command line arguments
for exchange of Geneve UDP packets
– it must support both IPv4 and IPv6 sockets
– addresses may be numeric IP addresses or host names URL
– ports may be numeric or a name listed in /etc/services
• Repeated specification of command line options may overwrite previously set values
• gnveu is only required to implemented a simplified version of draft-ietf-nvo3-geneve-16:
– it only has to create a single UDP connection to the server
– it can expect to receive replies to the local port it transmits from
– encoding entropy by using multiple source ports is not required
– it will act as a client talking to a server
• It only needs to support Geneve encapsulation of Ethernet (Geneve type: 0x6558) packets.
• Tunnels are uniquely identified by their Virtual Network Identifier (VNI)
– The VNI is used to specify the type of traffic to encapsulate.
2.5 Required Dependencies
gnveu must only use the following libraries and the APIs they provide to implement the above functionality.
2.5.1 libc
libc refers to the ISO or POSIX standard C library provided by UNIX and UNIX like operating systems. A
libc contains the APIs required by gnveu for such tasks as resolving host and service names to IP addresses
and ports, creating network sockets and connections, and opening and reading files.
2.5.2 libevent
According to, libevent:
. . . provides a mechanism to execute a callback function when a specific event occurs on a file
descriptor or after a timeout has been reached. Furthermore, libevent also support callbacks due
to signals or regular timeouts.
OpenBSD ships with libevent 1.4 with local patches. It is this version of libevent in the base system what
you are required to write gnveu against.
2.5.3 tap(4)
According to the tap(4) manual page:
The tap driver provides an Ethernet interface pseudo-device. Packets sent to this interface can be
read by a userland process and processed as desired. Packets written by the userland process are
injected back into the kernel networking subsystem.
2.6 Logging API
gnveu may use the log.c and log.h file supplied by the course, rather than implementing this functionality
The API and documentation is provided at If used, the code should copied
into the submitted assignment.
2.7 Restrictions
• gnveu must operate as a single process/thread, therefore it may not fork (after daemonising) or create
2.8 Recommendations
The focus of this assignment is event driven programming, not on creating new implementations of common
functionality. It is strongly recommended that the following APIs are used as part of your program:
• getopt(3) – get option character from command line argument list
• err(3), warn(3), etc – formatted error messages
• getaddrinfo(3) – host and service name to socket address structure
• gai_strerror(3) – get error message string from EAI_xxx error code
• strtonum(3) – reliably convert string value to an integer
• daemon(3) – run in the background
• ioctl(2) – control device, used to configure non-blocking file descriptor operation
3 Submission
Submission must be made electronically by committing to your Subversion repository on
In order to mark your assignment the markers will check out a1 from your repository. Code checked in to any
other part of your repository will not be marked.
As per the usage guidelines, you should only commit source code and Makefiles
4 Testing
4.1 Ethernet
A server is running on the IPv4 address of on port 3301 that implements a
Geneve UDP server. This server implements a virtual Ethernet switch, allowing Geneve UDP tunnels to
communicate, but has no support for IPv4 and IPv6 tunnels. The server has the following VNIs and IPv4
subnets configured:
• VNI 0:
IPv4 addresses can be requested via DHCP on all four networks. The server should support communication
between tunnels connected to the same networks.
4.2 Packet Inspection
Several tools are available that are capture and disect network packets for inspection. These may be used to
verify that the packets on the wire conform to the expected format. tcpdump(8) is available in the OpenBSD
base system, and supports disection of Geneve inside UDP.
4.3 tcpdump Update Required
You must update tcpdump by doing the following:
1) Make sure your code is backed up in your SVN folder before continuing.
2) Login into your openBSD VM as a normal user.
3) cd /usr
4) cvs -Qd co -P src/sys
5) cvs -Qd co -P src/lib
6) cvs -Qd co -P src/sbin
7) cvs -Qd co -P src/usr.sbin
8) cd src/usr.sbin/tcpdump
9) make obj
10) make
11) sudo make install
12) sudo reboot
13) To check that tcpdump is installed – run “man tcpdump” and you should see under the “-T” option,
4.4 tcpdump Command Example.
An example of it’s usage:
# tcpdump -v -e -i em0 -Tgeneve host and port 3301
tcpdump: listening on em0, link-type EN10MB
10:57:34.583486 bc:2c:55:36:7f:fb 74:88:2a:d4:b2:00 ip 88:
.3301 > [udp sum ok] gre [] 6558 fe:e1:ba:dd:8c
:f9 fe:e1:ba:da:ab:9c ip 42: > icmp: echo request (id:00
00 seq:0) [icmp cksum ok] (ttl 64, id 1, len 28) (ttl 64, id 1, len 74)