This document provides an overview of a presentation on Linux networking. The agenda includes topics like ARP, interface manipulation, network troubleshooting, routing, network bonding, network namespaces, kernel network parameters, and interview questions. It notes that the presentation will demonstrate over 30 commands related to networking and that there are often multiple ways to solve exercises. It encourages asking questions to aid learning.
Getting started with setting up embedded platform requires audience to understand some of the key aspects of Linux. This presentation deals with basics of Linux as an OS, Linux commands, vi editor, Shell features like redirection, pipes and shell scripting
LinuxCon 2015 Linux Kernel Networking WalkthroughThomas Graf
This presentation features a walk through the Linux kernel networking stack for users and developers. It will cover insights into both, existing essential networking features and recent developments and will show how to use them properly. Our starting point is the network card driver as it feeds a packet into the stack. We will follow the packet as it traverses through various subsystems such as packet filtering, routing, protocol stacks, and the socket layer. We will pause here and there to look into concepts such as networking namespaces, segmentation offloading, TCP small queues, and low latency polling and will discuss how to configure them.
Linux Tutorial For Beginners | Linux Administration Tutorial | Linux Commands...Edureka!
This Linux Tutorial will help you get started with Linux Administration. This Linux tutorial will also give you an introduction to the basic Linux commands so that you can start using the Linux CLI. Do watch the video till the very end to see all the demonstration. Below are the topics covered in this tutorial:
1) Why go for Linux?
2) Various distributions of Linux
3) Basic Linux commands: ls, cd, pwd, clear commands
4) Working with files & directories: cat, vi, gedit, mkdir, rmdir, rm commands
5) Managing file Permissions: chmod, chgrp, chown commands
6) Updating software packages from Linux repository
7) Compressing & Decompressing files using TAR command
8) Environment variables and Regular expressions
9) Starting and killing processes
10) Managing users
11) SSH protocol for accessing remote hosts
Présentation aux Geeks Anonymes Liège par Cyril Soldani, le 13 décembre 2017.
Page des Geeks Anonymes : https://www.recherche.uliege.be/cms/c_9463913/fr/geeks-anonymes
Getting started with setting up embedded platform requires audience to understand some of the key aspects of Linux. This presentation deals with basics of Linux as an OS, Linux commands, vi editor, Shell features like redirection, pipes and shell scripting
LinuxCon 2015 Linux Kernel Networking WalkthroughThomas Graf
This presentation features a walk through the Linux kernel networking stack for users and developers. It will cover insights into both, existing essential networking features and recent developments and will show how to use them properly. Our starting point is the network card driver as it feeds a packet into the stack. We will follow the packet as it traverses through various subsystems such as packet filtering, routing, protocol stacks, and the socket layer. We will pause here and there to look into concepts such as networking namespaces, segmentation offloading, TCP small queues, and low latency polling and will discuss how to configure them.
Linux Tutorial For Beginners | Linux Administration Tutorial | Linux Commands...Edureka!
This Linux Tutorial will help you get started with Linux Administration. This Linux tutorial will also give you an introduction to the basic Linux commands so that you can start using the Linux CLI. Do watch the video till the very end to see all the demonstration. Below are the topics covered in this tutorial:
1) Why go for Linux?
2) Various distributions of Linux
3) Basic Linux commands: ls, cd, pwd, clear commands
4) Working with files & directories: cat, vi, gedit, mkdir, rmdir, rm commands
5) Managing file Permissions: chmod, chgrp, chown commands
6) Updating software packages from Linux repository
7) Compressing & Decompressing files using TAR command
8) Environment variables and Regular expressions
9) Starting and killing processes
10) Managing users
11) SSH protocol for accessing remote hosts
Présentation aux Geeks Anonymes Liège par Cyril Soldani, le 13 décembre 2017.
Page des Geeks Anonymes : https://www.recherche.uliege.be/cms/c_9463913/fr/geeks-anonymes
netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers.
iptables is a user-space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different netfilter modules) and the chains and rules it stores.
Many systems use iptables/netfilter, Linux's native packet filtering/mangling framework since Linux 2.4, be it home routers or sophisticated cloud network stacks.
In this session, we will talk about the netfilter framework and its facilities, explain how basic filtering and mangling use-cases are implemented using iptables, and introduce some less common but powerful extensions of iptables.
Shmulik Ladkani, Chief Architect at Nsof Networks.
Long time network veteran and kernel geek.
Shmulik started his career at Jungo (acquired by NDS/Cisco) implementing residential gateway software, focusing on embedded Linux, Linux kernel, networking and hardware/software integration.
Some billions of forwarded packets later, Shmulik left his position as Jungo's lead architect and joined Ravello Systems (acquired by Oracle) as tech lead, developing a virtual data center as a cloud-based service, focusing around virtualization systems, network virtualization and SDN.
Recently he co-founded Nsof Networks, where he's been busy architecting network infrastructure as a cloud-based service, gazing at internet routes in astonishment, and playing the chkuku.
Tutorial: Using GoBGP as an IXP connecting routerShu Sugimoto
- Show you how GoBGP can be used as a software router in conjunction with quagga
- (Tutorial) Walk through the setup of IXP connecting router using GoBGP
SOSCON 2019.10.17
What are the methods for packet processing on Linux? And how fast are each packet processing methods? In this presentation, we will learn how to handle packets on Linux (User space, socket filter, netfilter, tc), and compare performance with analysis of where each packet processing is done in the network stack (hook point). Also, we will discuss packet processing using XDP, an in-kernel fast-path recently added to the Linux kernel. eXpress Data Path (XDP) is a high-performance programmable network data-path within the Linux kernel. The XDP is located at the lowest level of access through SW in the network stack, the point at which driver receives the packet. By using the eBPF infrastructure at this hook point, the network stack can be expanded without modifying the kernel.
Daniel T. Lee (Hoyeon Lee)
@danieltimlee
Daniel T. Lee currently works as Software Engineer at Kosslab and contributing to Linux kernel BPF project. He has interest in cloud, Linux networking, and tracing technologies, and likes to analyze the kernel's internal using BPF technology.
Here, you can learn all information about Shell Script.
1. What is Shell Script?
2. Types of Shell Script.
3. Use of Shell Script.
4. Command line of Shell Script.
5. Example of Shell Script.
Linux offers an extensive selection of programmable and configurable networking components from traditional bridges, encryption, to container optimized layer 2/3 devices, link aggregation, tunneling, several classification and filtering languages all the way up to full SDN components. This talk will provide an overview of many Linux networking components covering the Linux bridge, IPVLAN, MACVLAN, MACVTAP, Bonding/Team, OVS, classification & queueing, tunnel types, hidden routing tricks, IPSec, VTI, VRF and many others.
Using eBPF for High-Performance Networking in CiliumScyllaDB
The Cilium project is a popular networking solution for Kubernetes, based on eBPF. This talk uses eBPF code and demos to explore the basics of how Cilium makes network connections, and manipulates packets so that they can avoid traversing the kernel's built-in networking stack. You'll see how eBPF enables high-performance networking as well as deep network observability and security.
This presentation is an introduction to Ansible, an IT automation tool which can configure systems, deploy software, and orchestrate more advanced IT tasks such as continuous deployments or zero downtime rolling updates.
Video: https://www.youtube.com/watch?v=JRFNIKUROPE . Talk for linux.conf.au 2017 (LCA2017) by Brendan Gregg, about Linux enhanced BPF (eBPF). Abstract:
A world of new capabilities is emerging for the Linux 4.x series, thanks to enhancements that have been included in Linux for to Berkeley Packet Filter (BPF): an in-kernel virtual machine that can execute user space-defined programs. It is finding uses for security auditing and enforcement, enhancing networking (including eXpress Data Path), and performance observability and troubleshooting. Many new open source tools that have been written in the past 12 months for performance analysis that use BPF. Tracing superpowers have finally arrived for Linux!
For its use with tracing, BPF provides the programmable capabilities to the existing tracing frameworks: kprobes, uprobes, and tracepoints. In particular, BPF allows timestamps to be recorded and compared from custom events, allowing latency to be studied in many new places: kernel and application internals. It also allows data to be efficiently summarized in-kernel, including as histograms. This has allowed dozens of new observability tools to be developed so far, including measuring latency distributions for file system I/O and run queue latency, printing details of storage device I/O and TCP retransmits, investigating blocked stack traces and memory leaks, and a whole lot more.
This talk will summarize BPF capabilities and use cases so far, and then focus on its use to enhance Linux tracing, especially with the open source bcc collection. bcc includes BPF versions of old classics, and many new tools, including execsnoop, opensnoop, funcccount, ext4slower, and more (many of which I developed). Perhaps you'd like to develop new tools, or use the existing tools to find performance wins large and small, especially when instrumenting areas that previously had zero visibility. I'll also summarize how we intend to use these new capabilities to enhance systems analysis at Netflix.
Accelerating Envoy and Istio with Cilium and the Linux KernelThomas Graf
This talk will provide an introduction to injection options of Envoy and then deep dive into ongoing Linux kernel work that enables injecting Envoy while introducing as little latency as possible.
The servicemesh and the sidecar proxy model are on a steep trajectory to redefine many networking and security use cases. This talk explains and demos a new socket redirect Linux kernel technology that allows running Envoy with similar performance as if the sidecar was linked to the application using a UNIX domain socket. The talk will also give an outlook on how Envoy can use the recently merged kernel TLS functionality to gain access to the clear text payload transparently for end to end encrypted applications without requiring to decrypt and re-encrypt any data to further reduce the overhead and latency.
In this workshop we will make a brief introduction to the basics of networking: IP addresses, MAC addresses, DNS, DHCP. Concepts as a router, gateway and firewall are explained. Then we will see in practice how to share files on a local network (NFS, Samba), establish a FTP connection, or log on to another (Linux) machine remotely (SSH, VNC, RDP). Finally, we review some useful networking tools like ping, netstat, lookup, port scan, traceroute, whois.
netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers.
iptables is a user-space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different netfilter modules) and the chains and rules it stores.
Many systems use iptables/netfilter, Linux's native packet filtering/mangling framework since Linux 2.4, be it home routers or sophisticated cloud network stacks.
In this session, we will talk about the netfilter framework and its facilities, explain how basic filtering and mangling use-cases are implemented using iptables, and introduce some less common but powerful extensions of iptables.
Shmulik Ladkani, Chief Architect at Nsof Networks.
Long time network veteran and kernel geek.
Shmulik started his career at Jungo (acquired by NDS/Cisco) implementing residential gateway software, focusing on embedded Linux, Linux kernel, networking and hardware/software integration.
Some billions of forwarded packets later, Shmulik left his position as Jungo's lead architect and joined Ravello Systems (acquired by Oracle) as tech lead, developing a virtual data center as a cloud-based service, focusing around virtualization systems, network virtualization and SDN.
Recently he co-founded Nsof Networks, where he's been busy architecting network infrastructure as a cloud-based service, gazing at internet routes in astonishment, and playing the chkuku.
Tutorial: Using GoBGP as an IXP connecting routerShu Sugimoto
- Show you how GoBGP can be used as a software router in conjunction with quagga
- (Tutorial) Walk through the setup of IXP connecting router using GoBGP
SOSCON 2019.10.17
What are the methods for packet processing on Linux? And how fast are each packet processing methods? In this presentation, we will learn how to handle packets on Linux (User space, socket filter, netfilter, tc), and compare performance with analysis of where each packet processing is done in the network stack (hook point). Also, we will discuss packet processing using XDP, an in-kernel fast-path recently added to the Linux kernel. eXpress Data Path (XDP) is a high-performance programmable network data-path within the Linux kernel. The XDP is located at the lowest level of access through SW in the network stack, the point at which driver receives the packet. By using the eBPF infrastructure at this hook point, the network stack can be expanded without modifying the kernel.
Daniel T. Lee (Hoyeon Lee)
@danieltimlee
Daniel T. Lee currently works as Software Engineer at Kosslab and contributing to Linux kernel BPF project. He has interest in cloud, Linux networking, and tracing technologies, and likes to analyze the kernel's internal using BPF technology.
Here, you can learn all information about Shell Script.
1. What is Shell Script?
2. Types of Shell Script.
3. Use of Shell Script.
4. Command line of Shell Script.
5. Example of Shell Script.
Linux offers an extensive selection of programmable and configurable networking components from traditional bridges, encryption, to container optimized layer 2/3 devices, link aggregation, tunneling, several classification and filtering languages all the way up to full SDN components. This talk will provide an overview of many Linux networking components covering the Linux bridge, IPVLAN, MACVLAN, MACVTAP, Bonding/Team, OVS, classification & queueing, tunnel types, hidden routing tricks, IPSec, VTI, VRF and many others.
Using eBPF for High-Performance Networking in CiliumScyllaDB
The Cilium project is a popular networking solution for Kubernetes, based on eBPF. This talk uses eBPF code and demos to explore the basics of how Cilium makes network connections, and manipulates packets so that they can avoid traversing the kernel's built-in networking stack. You'll see how eBPF enables high-performance networking as well as deep network observability and security.
This presentation is an introduction to Ansible, an IT automation tool which can configure systems, deploy software, and orchestrate more advanced IT tasks such as continuous deployments or zero downtime rolling updates.
Video: https://www.youtube.com/watch?v=JRFNIKUROPE . Talk for linux.conf.au 2017 (LCA2017) by Brendan Gregg, about Linux enhanced BPF (eBPF). Abstract:
A world of new capabilities is emerging for the Linux 4.x series, thanks to enhancements that have been included in Linux for to Berkeley Packet Filter (BPF): an in-kernel virtual machine that can execute user space-defined programs. It is finding uses for security auditing and enforcement, enhancing networking (including eXpress Data Path), and performance observability and troubleshooting. Many new open source tools that have been written in the past 12 months for performance analysis that use BPF. Tracing superpowers have finally arrived for Linux!
For its use with tracing, BPF provides the programmable capabilities to the existing tracing frameworks: kprobes, uprobes, and tracepoints. In particular, BPF allows timestamps to be recorded and compared from custom events, allowing latency to be studied in many new places: kernel and application internals. It also allows data to be efficiently summarized in-kernel, including as histograms. This has allowed dozens of new observability tools to be developed so far, including measuring latency distributions for file system I/O and run queue latency, printing details of storage device I/O and TCP retransmits, investigating blocked stack traces and memory leaks, and a whole lot more.
This talk will summarize BPF capabilities and use cases so far, and then focus on its use to enhance Linux tracing, especially with the open source bcc collection. bcc includes BPF versions of old classics, and many new tools, including execsnoop, opensnoop, funcccount, ext4slower, and more (many of which I developed). Perhaps you'd like to develop new tools, or use the existing tools to find performance wins large and small, especially when instrumenting areas that previously had zero visibility. I'll also summarize how we intend to use these new capabilities to enhance systems analysis at Netflix.
Accelerating Envoy and Istio with Cilium and the Linux KernelThomas Graf
This talk will provide an introduction to injection options of Envoy and then deep dive into ongoing Linux kernel work that enables injecting Envoy while introducing as little latency as possible.
The servicemesh and the sidecar proxy model are on a steep trajectory to redefine many networking and security use cases. This talk explains and demos a new socket redirect Linux kernel technology that allows running Envoy with similar performance as if the sidecar was linked to the application using a UNIX domain socket. The talk will also give an outlook on how Envoy can use the recently merged kernel TLS functionality to gain access to the clear text payload transparently for end to end encrypted applications without requiring to decrypt and re-encrypt any data to further reduce the overhead and latency.
In this workshop we will make a brief introduction to the basics of networking: IP addresses, MAC addresses, DNS, DHCP. Concepts as a router, gateway and firewall are explained. Then we will see in practice how to share files on a local network (NFS, Samba), establish a FTP connection, or log on to another (Linux) machine remotely (SSH, VNC, RDP). Finally, we review some useful networking tools like ping, netstat, lookup, port scan, traceroute, whois.
Presented at LISA18: https://www.usenix.org/conference/lisa18/presentation/babrou
This is a technical dive into how we used eBPF to solve real-world issues uncovered during an innocent OS upgrade. We'll see how we debugged 10x CPU increase in Kafka after Debian upgrade and what lessons we learned. We'll get from high-level effects like increased CPU to flamegraphs showing us where the problem lies to tracing timers and functions calls in the Linux kernel.
The focus is on tools what operational engineers can use to debug performance issues in production. This particular issue happened at Cloudflare on a Kafka cluster doing 100Gbps of ingress and many multiple of that egress.
XCon 2014 => http://xcon.xfocus.org/
In the past was quite common to exploit heap / pool manager vulnerabilities attacking its internal linked structures. However current memory management improve a lot and at current date it is quite ineffective to attack heap in this way. But still those techniques come into hand when we start to looking at linked structures widespread throughout kernel that are unfortunately not hardened enough.
In this presentation we will examine power of these vulnerabilities by famous example “CVE – 2013 - 3660”. Showing bypass on ‘lazy’ assertions of _LIST_ENTRY, present exploitation after party and teleport to kernel.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
3. Before we start...
▪ This presentation is not about learning networking concepts.
▪ We are going to see over 30 commands
▫ Many of them overlap so you don’t need to remember them all. Take
whatever works for you the best.
▪ There is more than one way to solve some of the exercises.
▪ Ask questions and start discussions as this is one of the best ways to learn.
5. ping - test the reachability of a host
[arie@fedora ~]$ ping 8.8.8.8
64 bytes from 8.8.8.8: icmp_seq=1 ttl=120 time=66.2 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=120 time=66.2 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=120 time=66.1 ms
[arie@
What protocol does the
‘ping’ command uses?
Do you know?
● Used to check whether a given host is reachable
● By default, it will not stop until sending an interrupt
[arie@fedora ~]$ ping 8.8.8.8
64 bytes from 8.8.8.8: icmp_seq=1 ttl=120 time=66.1 ms
--- 8.8.8.8 ping statistics ---
^C
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 66.130/66.130/66.130/0.000 ms
6. ping - more examples
[arie@fedora ~]$ ping -s 250 8.8.8.8
258 bytes from 8.8.8.8: icmp_seq=1 ttl=120 time=66.2 ms
● Control packet size
[arie@
Will a packet size of
2000 will work?
Do you know?
[arie@fedora ~]$ ping -c 2 8.8.8.8
64 bytes from 8.8.8.8: icmp_seq=1 ttl=120 time=66.2 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=120 time=66.2 ms
● Control number of packets
● Try ‘ping -a 8.8.8.8’
○ What it does?
7. List network interfaces
[arie@fedora ~]$ ip link show # you can also use ‘ip l’
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
state UP mode DEFAULT group default qlen 1000
link/ether 8c:16:45:32:99:d7 brd ff:ff:ff:ff:ff:ff
● Do not use ‘ifconfig’. It’s deprecated!
● Why do we need the loopback device?
● There is a separate manual for ‘ip link’ (man ip-link)
● List devices and show their attributes
○ You can learn a lot of from the output: MTU, MAC, state
8. List network interfaces with their addresses
[arie@fedora ~]$ ip addr # You can also use ‘ip a’
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s25f5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
state UP group default qlen 1000
link/ether 2b:12:63:62:55:d4 brd ff:ff:ff:ff:ff:ff
inet 190.40.2.126/24 brd 190.40.2.255 scope global dynamic noprefixroute enp0s31f6
valid_lft 83174sec preferred_lft 83174sec
● Show network interfaces but this time with their IP addresses
9. ethtool - query and manipulate driver and hardware settings
[arie@fedora ~]$ sudo ethtool my_interface
Settings for my_interface:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
...
Current message level: 0x00000007 (7)
drv probe link
Link detected: yes
10. ethtool - The Cool Features
[arie@fedora ~]$ sudo ethtool -p interface_name
● Don’t know which physical port a specific interface is using? Make the
interface led blinking!
[arie@fedora ~]$ sudo ethtool -t interface_name
● Run tests to check your network interface
[arie@fedora ~]$ sudo ethtool -S interface_name
● Tons of statistics!
● We’ll see more of ethtool later on
11. lshw - the hardware perspective
● You can use lshw to get the hardware information on your network devices
[arie@fedora ~]$ lshw -class network
*-network
description: Ethernet interface
product: Ethernet Connection (2) I219-LM
vendor: Intel Corporation
physical id: 1f.6
logical name: enp0s31f6
serial: 2b:12:55:17:25:c2
size: 1Gbit/s
capacity: 1Gbit/s
capabilities: bus_master cap_list ethernet physical tp 10bt 10bt-fd
configuration: autonegotiation=on driver=e1000e driverversion=3.2.6-k duplex=full
● You can obtain interesting information like:
○ Type of the card (product + vendor)
○ Configuration and capabilities (duplex, driver, …)
12. lspci - the hardware perspective 2
● You can also use lspci
[arie@fedora ~]$ lspci | grep -E -i 'network|ethernet'
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (2) I219-LM (rev 31)
04:00.0 Network controller: Intel Corporation Wireless 8260 (rev 3a)
● As you can see, ‘lshw’ might be a better choice :)
13. Network Interfaces - The Proc Way
● You can see network interfaces list by looking at ‘/proc/net/dev’
[arie@fedora ~]$ cat /proc/net/dev
Inter-| Receive | Transmit
face |bytes packets errs drop fifo frame compressed multicast|bytes
enp0s31f6: 686290777 697340 0 0 0 0 0 0
virbr0: 0 0 0 0 0 0 0 0 0 0
● It provides basic statistics like how many packets sent and received
15. Display ARP cache
● ARP is used for converting an IP address to a physical address
● ARP cache is where such coversion entries are stored
● Use ‘ip neigh’ to display the ARP cache
○ It replaced the ‘arp’ command
[arie@fedora ~]$ ip neigh
190.41.2.25 dev enp0s31f6 lladdr 15:b1:52:5c:25:17 STALE
10.52.21.52 dev wlp4s0 lladdr 12:3a:45:b2:ab:55 STALE
● You can also use ‘dev <device_name>’ to see ARP entries related to a specific
device
● Now try reading ‘/proc/net/arp’
○ Does it contains a different data?
16. Add ARP entry
● ip neigh can be used to insert a permanent ARP cache
[arie@fedora ~]$ ip neigh add 2.2.2.2 lladdr 00:b1:6a:6a:11:c2 dev eth0 nud permanent
● You can change an ARP entry after it was added
[arie@fedora ~]$ ip neigh change 2.2.2.2 lladdr 00:c1:6a:6a:11:c3 dev eth0
17. Remove ARP Entry
● You can remove a specific ARP entry by specifying the IP address and device
[arie@fedora ~]$ ip neigh del 2.2.2.2 dev eth0
● You can also flush all the learned (not permanent) entries
[arie@fedora ~]$ ip neigh flush dev eth0
19. The Basics - Exercise
ping
ip a
ip l
lshw
lspci
ip neigh
Commands mentioned in this section
● List the network interfaces on your host
● Choose one IP address from the list and ping it with 3 packets of size 100
● Check if the MAC address of the interface you chose is in the ARP table
○ No? Yes? Why? :)
● Add the following entry in your ARP cache:
○ IP address 3.3.3.3
○ MAC: 00:b1:6b:6b:11:c6
● Verify it’s there. Once verified, remove it.
Note: whenever you forget what argument you need to use, try using ‘man’
20. The Basics - Exercise Solution
[arie@fedora ~]$ ip a
[arie@fedora ~]$ ping -c 3 -s 100 x.x.x.x
[arie@fedora ~]$ arp | grep <MAC>
[arie@fedora ~]$ ip neigh add 3.3.3.3 lladdr 00:b1:6b:6b:11:c6 dev eth0 nud permanent
22. Network Manager
● The default manager for networking service in RHEL 7
● In older releases you might need to install the package ‘NetworkManager’
● You can also install a similar version on Ubuntu
● NM provides you the following tools
○ nmcli (terminal)
○ nmtui (tui, if not installed you can install ‘NetworkManager-tui’ to get it)
○ nm-connection-editor (GUI)
● The network manager daemon is called ‘NetworkManager’
[arie@ubuntu ~]$ sudo apt-get install network-manager
[arie@fedora ~]$ sudo systemctl status NetworkManager
● NetworkManager.service - Network Manager
Loaded: loaded (/usr/lib/systemd/system/NetworkManager.servi…)
Active: active (running) since Tue 2005-09-04 09:15:08 IDT; 34min ago
23. Network Configuration Files
● You can change network configuration by editing network configuration files
instead of using the tui or gui tools
● Red Hat based operating systems
○ /etc/sysconfig/network-scripts/ifcfg-<interface_name>
● Ubuntu
○ /etc/network/interfaces
○ etc/network/interfaces.d/*
● Once you added/modified an interface
[arie@fedora ~]$ sudo ip link set <interface> down
[arie@fedora ~]$ sudo ip link set <interface> up
● Where NM is used, you can also do the following
[arie@fedora ~]$ sudo nmcli connection reload # for all interfaces
[arie@fedora ~]$ sudo nmcli con load <interface_configuration_file> # for a specific interfacce
24. Network Configuration Files - Example
NAME="eth0"
DEVICE="eth0”
ONBOOT="yes"
BOOTPROTO="dhcp"
TYPE="Ethernet"
iface eth0 inet static
address 192.168.1.1
netmask 255.255.255.0
iface eth0 inet dhcp
DEVICE="eth0"
BOOTPROTO="static"
ONBOOT="yes"
TYPE="Ethernet"
IPADDR=10.0.0.42
NETMASK=255.255.255.0
BROADCAST=10.0.0.255
GATEWAY=10.0.0.1
Red Hat Based OS Ubuntu
25. Add a dummy interface
[arie@fedora ~]$ sudo ip link add dumdum type dummy
● Add a dummy interface
[arie@fedora ~]$ sudo ip link set dumdum up
● Bring up the dummy interface
● Is it up? How to check?
26. Assign an IP address
[arie@fedora ~]$ sudo ip addr add 192.168.0.50/24 dev dumdum
● Assign an IP address to our dummy interface
[arie@fedora ~]$ sudo ip addr add 192.168.0.50/255.255.255.0 dev dumdum
● Is the following command different from the previous one?
● Verify it has an IP address and ping it
[arie@fedora ~]$ ip a show dumdum && ping -c 1192.168.0.50
dumdum: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
qlen 1000
link/ether 06:f1:a6:1b:c9:f5 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.50/24 scope global dumdum
valid_lft forever preferred_lft forever
27. Set broadcast address
[arie@fedora ~]$ sudo ip addr add broadcast 192.168.0.255 dev dumdum
● Set broadcast address
● You can also do it while assigning an IP address
[arie@fedora ~]$ sudo ip addr add 192.168.0.50/24 broadcast 192.168.0.255 dev dumdum
28. Change MTU size
[arie@fedora ~]$ sudo ip link set dumdum mtu 1800
● Verify it’s the new MTU size
● Will it survive a reboot?
● Set it permanently for Red Hat based OSs
NAME="enp0s31f6"
MTU=”1800”
BOOTPROTO="static" # IMPORTANT
● Set it permanently for interface in Ubuntu
iface eth0 inet static
address 192.168.0.1
...
netmask 255.255.255.0
mtu 1800
29. Change speed
[arie@fedora ~]$ sudo ethtool -s eth0 speed 100
● Set it permanently for Red Hat based OSs
NAME="enp0s31f6"
MTU=”1800”
BOOTPROTO="static"
ETHTOOL_OPTS="speed 100”
● Set it permanently for interface in Ubuntu
pre-up /usr/sbin/ethtool -s eth0 100
30. Remove an interface
[arie@fedora ~]$ sudo ip link set dumdum down
● Bring down the dummy interface we created
[arie@fedora ~]$ sudo ip link del dumdum
● Delete the dummy interface
32. Interfaces Manipulation - Exercise
ip link del/add
ip link set
ethtool -s eth0 speed <number>
nmcli connection reload
nmcli connection load <path>
Commands mentioned in this section
● Add a dummy interface called “pita”
● Assign it whatever IP you would like
● Ping the IP address you assigned with four packets of size 140
● Set the MTU to 1900
● Remove the dummy interface you created
33. Interfaces Manipulation - Exercise Solution
[arie@fedora ~]$ sudo ip link add pita type dummy
[arie@fedora ~]$ sudo ip addr add 192.168.1.4/24 dev pita
[arie@fedora ~]$ ping -c 4 -s 140 192.168.1.4
[arie@fedora ~]$ sudo ip link set pita mtu 1900
[arie@fedora ~]$ sudo ip link set pita down
[arie@fedora ~]$ sudo ip link del pita
35. Recap
● Some of the tools we have seen so far can be used to obtain some information
on what is going on in our system from networking perspective. Let’s recall what
we saw
● Ethtool statistics
[arie@fedora ~]$ sudo ethtool -S <interface_name>
● ethtool interface testing
[arie@fedora ~]$ sudo ethtool -t <interface_name>
● Looking at /proc/net/dev
● Time to move to the next level
36. netstat - network connections
● Display information about the networking subsystem
○ By default it displays a list of open sockets
[arie@fedora ~]$ netstat
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 mario-p8-kvm-03-gue:39240 api.ohsnap.io:https ESTABLISHED
tcp 0 0 luigi-p8-kvm-03-gue:42310 tumtum.shlipshlop.:http TIME_WAIT
● Common arguments
○ -n to use IP addresses instead of hostname
○ -t to show only tcp connections
○ -p to show the pid of the program
○ -l to show only listening sockets
● Try it yourself: ‘netstat -tnlp’
37. netstat - statistics and routing
● Netstat is also able to show you information on routing tables
[arie@fedora ~]$ netstat -r
Destination Gateway Genmask Flags MSS Window irtt Iface
default Box.Home 0.0.0.0 UG 0 0 0 wlp4s0
192.168.14.0 0.0.0.0 255.255.255.0 U 0 0 0 wlp4s0
● And a LOT of statistics
[arie@fedora ~]$ netstat -s
38. lsof
● Lists open files
○ Isn’t it a storage tool? Perhaps, but everything in Linux is a file and
that includes a network socket
[arie@fedora ~]$ lsof -i
chrome 9827 abregman 133u IPv4 170 0t0 TCP localhost:57654->ec2-54om:https (ESTABLISHED)
chrome 9827 abregman 179u IPv4 02 0t0 TCP localhost:51928->ec2s.com:https (ESTABLISHED)
● You can make it more specific by specifying hostname, port or a service
[arie@fedora ~]$ lsof -i :openflow
[arie@fedora ~]$ lsof -i :smtp
[arie@fedora ~]$ lsof -i :2312
[arie@fedora ~]$ lsof -i @google.com
39. lsof - continue
● Side question: How to know which network services exists and what are their ports?
[arie@fedora ~]$ cat /etc/services
tcpmux 1/tcp # TCP port service multiplexer
tcpmux 1/udp # TCP port service multiplexer
rje 5/tcp # Remote Job Entry
rje 5/udp # Remote Job Entry
● You can see all the open files owned by a specific process
[arie@fedora ~]$ lsof -p <pid>
40. Packet Sniffers
● Probably the most powerful type of tools for network analyzing and
troubleshooting
● Also known as
○ Packet Analyzer
○ Network sniffer
○ Packet Capture
● Allows you to
○ Monitor network usage and status
○ Analyze network problems
○ Verify security modifications
○ And so much more...
● There are quite a lot of packet sniffers
○ tcpdump
○ Wireshark
○ Dhcpdump
○ httpry
41. Packet Sniffers - tcpdump
● Probably the most popular one
● Installed by default
● Easy start using:
[arie@fedora ~]$ sudo tcpdump
19:48:04.393650 IP 10.0.2.15.ssh > 10.0.2.2.34154: Flags [P.], seq 2880236:2880288, ack 5797, win
36192, length 52
19:48:04.393703 IP 10.0.2.15.ssh > 10.0.2.2.34154: Flags [P.], seq 2880288:2880340, ack 5797, win
36192, length 52
● Overwhelmed already? :)
42. Packet Sniffers - tcpdump
● Capture packets from all interfaces
[arie@fedora ~]$ sudo tcpdump -i any
● Capture packets from a specific interface
[arie@fedora ~]$ sudo tcpdump -i eth0
● Track only SSH traffic
[arie@fedora ~]$ sudo tcpdump port 22
● Port range
[arie@fedora ~]$ sudo tcpdump port 22-50
43. Packet Sniffers - tcpdump - more examples
● Looking for pings?
[arie@fedora ~]$ sudo tcpdump icmp
● Traffic related to host x.x.x.x
[arie@fedora ~]$ sudo tcpdump host x.x.x.x
● Traffic related to host x.x.x.x (when it’s the source)
[arie@fedora ~]$ sudo tcpdump src x.x.x.x
● Traffic related to host x.x.x.x (when it’s the destination)
[arie@fedora ~]$ sudo tcpdump dst x.x.x.x
44. Packet Sniffers - wireshark
● Similar to tcpdump by concept
● Known for its GUI
● Both wireshark and tcpdump use libpcap for capturing packets
[arie@fedora ~]$ sudo wireshark # for launching GUI
[arie@fedora ~]$ sudo tshark # for using CLI
1 0.000000000 10.0.2.2 → 10.0.2.15 SSH 90 Client: Encrypted packet (len=36)
2 0.000271278 10.0.2.15 → 10.0.2.2 SSH 90 Server: Encrypted packet (len=36)
3 0.000724602 10.0.2.2 → 10.0.2.15 TCP 60 34154 → 22 [ACK] Seq=37 Ack=37 Win=65535
4 0.216305358 10.0.2.2 → 10.0.2.15 SSH 90 Client: Encrypted packet (len=36)
5 0.216633149 10.0.2.15 → 10.0.2.2 SSH 90 Server: Encrypted packet (len=36)
6 0.217004223 10.0.2.2 → 10.0.2.15 TCP 60 34154 → 22 [ACK] Seq=73 Ack=73 Win=65535
7 0.399682715 10.0.2.2 → 10.0.2.15 SSH 90 Client: Encrypted packet (len=36)
45. Packet Sniffers - wireshark
● Capture packet from all interfaces
[arie@fedora ~]$ sudo tshark -i any
● Capture packets from a specific interface
[arie@fedora ~]$ sudo tshark -i eth0 -w output.pcap
● Track only SSH traffic
[arie@fedora ~]$ sudo tshark port 22
● All packets related to host x.x.x.x
[arie@fedora ~]$ sudo tshark host x.x.x.x
47. Network Troubleshooting - Exercise
lsof -i
netstat -tnlp
netstat -r
netstat -s
tshark
wireshark
tcpdump
Commands mentioned in this section
● Count how many active connections there are
● Sniffing (you can stop it after 1-2 seconds)
○ Save to a file all the traffic related to DNS
○ Save to a file all the UDP traffic
○ Save to a file all the traffic sent to through your default gateway
50. Display Routing Table
[arie@fedora ~]$ ip route # You can also use ‘ip r’
default via 10.55.125.254 dev wlp4s0 proto dhcp metric 600
10.31.6.0/21 dev enp0s31f6 proto kernel scope link src 10.31.6.126 metric 100
10.22.66.0/24 dev wlp4s0 proto kernel scope link src 10.22.66.177 metric 600
192.168.1.0/24 dev virbr0 proto kernel scope link src 192.168.1.1 linkdown
● Ip can be used also for displaying the routing table
● First field - destination. Where the packet is sent.
● dev - through which device they will be sent
● proto - who or what added the route entry
● src - the IP source address
● Scope - an indicator to the distance to the destination address
○ Link - LAN
○ Default is global
[arie@
Can you have more
than one default entry?
Do you know?
51. Add Routes
[arie@fedora ~]$ sudo ip route add 190.40.5.1 via 10.0.2.15
● Add a static route to a host IP address
[arie@fedora ~]$ sudo ip route add 190.40.5.0/24 via 10.0.2.15
● Add a static route to a network
[arie@fedora ~]$ vi /etc/sysconfig/network
190.20.1.0/24 via 192.168.2.1 eth0
● Permanently in a file (Red Hat):
52. Add Routes - continue
[arie@fedora ~]$ sudo vi /etc/network/interfaces
iface eth0 inet static
address 192.168.2.2
netmask 255.255.255.0
up route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.254
● Permanently in a file (Ubuntu):
[arie@fedora ~]$ sudo ip route add default via 192.168.1.254
● Add a default gateway
● How to verify a route is working?
53. traceroute
● Shows you the hops (travel stations) from your local machine to the one
you specify
● It is used for networking troubleshooting and is a great tool for checking
routing issues
● How it works?
○ Using TTL
○ First, it sends a packet with TTL=1. When the first router gets it, it
will exceed the TTL and so the router will drop the packet but will
reply to the sender with an exceed message
○ Then, the sender will increase TTL to 2 and send it again.
○ The process repeats until the packet arrived its destination
54. traceroute - usage
● The usage is quite straightforward
[arie@fedora ~]$ traceroute redhat.com
traceroute to redhat.com (10.1.2.3), 30 hops max, 60 byte packets
1 blabla.redhat.com (10.52.36.252) 2.042 ms 2.244 ms 2.468 ms
2 190.40.2.10 (190.40.2.10) 0.308 ms 0.300 ms 0.426 ms
3 180.50.5.1 (180.50.5.1) 202.564 ms 202.587 ms 202.596 ms
● First line in the output specifies the destination IP, number of maximal
hops and size of packets that will be used
● Rest of the lines describe: hop (name and IP) and packet round trip times
● If you three asterisks (* * *) it means hop is not reachable
○ Firewall
○ Network Congestion
55. mtr - the best of both
● mtr = ping + traceroute
[arie@fedora ~]$ mtr --report redhat.com
Start: 2018-09-05T15:45:32+0300
HOST: dblabla.ran.redhat.com Loss% Snt Last Avg Best Wrst StDev
1.|-- blabla.ran.redhat 0.0% 10 1.3 1.7 0.7 2.6 0.6
2.|-- 194.40.2.10 0.0% 10 22.8 37.6 12.1 94.5 36.0
3.|-- 190.55.2.1 0.0% 10 0.7 0.6 0.4 0.7 0.1
57. Network Bonding
[arie@fedora ~]$ sudo modprobe bonding
● Bind two or more network interfaces together into a one logical interface
● Why?
○ Increasing bandwidth
○ Redundancy
● Requirements
○ Kernel bonding module
● Terminology
○ Master - the logical new interface
○ Slaves - the existing interfaces used for the bonding
58. Network Bonding - Modes
● Balance round robin
○ Mode 0
○ Round Robin
○ Fault Tolerance
● Active Backup
○ Mode 1
○ Only one is active
○ Fault tolerance
● Balance XOR
○ Mode 2
○ Similar to mode 0 but based on MAC XOR’d with destination address
59. Network Bonding - Modes
● Broadcast
○ Mode 3
○ Data received by all interfaces
○ Fault Tolerance
● 802.3ad
○ Mode 4
○ Dynamic link aggregation
○ Slaves share the same properties
● Balance TLB (transmit load balancing)
○ Mode 5
○ Data received by the interface with the least current traffic load
● Balance ALB (adaptive load balancing)
○ Mode 6
○ Balance TLB + Load balancing using ARP negotiations
60. Network Bonding - RHEL/CentOS/Fedora
● Configure bond interface
○ vi /etc/sysconfig/network-scripts/ifcfg-bond
DEVICE=bond
TYPE=Bond
IPADDR…
● Configure slaves
○ vi /etc/sysconfig/network-scripts/ifcfg-eth0 (one of several slaves)
DEVICE=eth0
TYPE=Ethernet
SLAVE=yes
MASTER=bond
61. Network Bonding - How To in RHEL/CentOS/Fedora
● Define mode
○ vi /etc/modprobe.d/bonding.conf
alias bond bonding
Options bond mode=1
● Bring the new bond interface up
[arie@fedora ~]$ sudo ip link set bond up
62. Network Bonding - Ubuntu
● Configure bond interface and slaves
○ vi /etc/network/interface
auto eth0
iface eth0 inet manual
bond-master bond0
bond-primary eth0
auto eth1
iface eth1 inet manual
bond-master bond0
iface bond inet static
address 192.168.1.30
gateway 192.168.1.254
netmask 255.255.255.0
bond-mode active-backup
● Restart networking and bring up the bond interface
64. Network Namespaces
● By default, the network stack in your OS (interfaces, routing table, …) is shared
across the OS
● If one would like to have a separate stack with its own interfaces and routing
table, independent from any other stack, the network namespace is the way to
achieve that
● Network namespaces is used by many projects
○ OpenStack
○ Mininet
○ Docker
65. Network Namespaces - Usage
● Create your first network namespace
[arie@fedora ~]$ sudo ip netns add ns1
● List namespaces
[arie@fedora ~]$ sudo ip netns list
ns1
[arie@fedora ~]$ sudo ip netns del ns1
● Remove a network namespace
66. ● Once a network namespace was created a corresponding file is created at
/var/run/netns
● You can execute commands inside a network namespace with ‘ip nents exec’
[arie@fedora ~]$ sudo ip netns exec ns1 ip a
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
[arie@
Are network namespaces
persistent across system
reboots?
Do you know?
Network Namespaces - Usage
● You can work fluently inside a namespace by running a shell
[arie@fedora ~]$ sudo ip netns exec ns1 bash
[root@fedora ~]$
67. ● You can assign an interface from the default namespace to your newly created
namespace
[arie@fedora ~]$ sudo ip link set eth0 netns ns1
Network Namespaces - Usage
68. ● Special type that provides you a pair of two interfaces (you can’t have one
without the other)
● Perfect for namespace scenarios as it allows you to have one end in a network
namespace and the other in another network namespace or in the global
namespace
● You can add veth interfaces with the ip command
[arie@fedora ~]$ sudo ip link add v0 type veth peer name v1
Side topic: veth interfaces
70. Kernel Parameters
● You can modify over thousand of kernel runtime parameters that will allow you
to change drastically the behaviour of your OS
● Many of them are network related parameters
● Use the following command to see exactly how many parameters you can
change
[arie@fedora ~]$ sudo sysctl -a | wc -l
1684
● We’ll review some of the more common and interesting parameters you can change
○ For a full list (with an explanation) I recommend to visit the following site
71. Changing Kernel Parameters
[arie@fedora ~]$ sysctl net.ipv4.ip_forward
● Obtain the value of a specific kernel parameter
[arie@fedora ~]$ sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward=1
● Modify a kernel parameter
● We can also do it with writing to proc
[arie@fedora ~]$ echo 1 > /proc/sys/net/ipv4/ip_forward
● To change it permanently (reboot persistent) write to /etc/sysctl.conf
[arie@fedora ~]$ echo “net.ipv4.ip_forward=1” >> /etc/sysctl.conf
72. Forward Packets
● Some kernels will not forward automatically packets that meant for someone
else
● In order to turn our server into a kind of router, we need to enable packet
forwarding
[arie@fedora ~]$ sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward=1
● Note that this is not the only step required for turning our Linux server into a router
○ Modification of iptables rules is also needed but we’ll not cover it here
73. Ignore Broadcast Messages
● Broadcast messages can be bad for your (server’s) health
○ Smurf Attack
● One can ignore such messages by setting the following parameter to 1
[arie@fedora ~]$ echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
75. Final Exercise
ip netns exec <ns_name> <command>
ip netns del <ns_name>
ip netns add <ns_name>
Ip link set <interface> netns <ns_name>
Ip link add
Relevant commands
● Add two network namespaces (ns1 and ns2)
● In the default/global namespace add veth interface pair (called v1 and v2)
● Move v1 interface to namespace ns1
● Move v2 interface to namespace ns2
● Assign IP address to v1 (10.1.1.2) and to v2 (10.1.1.3)
● Bring them (v1 and v2) up
● Enable IPv4 forwarding
● Ping from ns1 to ns2
● Ping from ns2 to ns1
76. Final Exercise - Solution
[arie@fedora ~]$ sudo ip netns add ns1
[arie@fedora ~]$ sudo ip netns add ns2
[arie@fedora ~]$ sudo ip link add v1 type veth peer name v2
[root@fedora ~]$ sudo ip link set v1 netns ns1
[root@fedora ~]$ sudo ip link set v2 netns ns2
[root@fedora ~]$ sudo ip netns exec ns1 ip addr add 10.1.1.3/16 dev v1
[root@fedora ~]$ sudo ip netns exec ns2 ip addr add 10.1.1.4/16 dev v2
[root@fedora ~]$ sudo ip netns exec ns1 ip link set v1 up
[root@fedora ~]$ sudo ip netns exec ns2 ip link set v2 up
[root@fedora ~]$ sysctl -w net.ipv4.ip_forward=1 # this step is not required. Just
wanted you to practice setting kernel parameters :P
[root@fedora ~]$ sudo ip netns exec ns1 ping 10.1.1.4
[root@fedora ~]$ sudo ip netns exec ns2 ping 10.1.1.3
78. Interview Questions - Theory
● What is the difference between TCP and UDP?
● How TCP works? What is the 3 way handshake protocol?
● What is a MAC address? Why do we need it?
● What is ARP?
● Why IPv6 was invented?
● Describe the following network devices: switch, router and a hub
● What is TTL (time-to-live)? What is the default value in Linux?
● What is NAT?
● DNS is using TCP or UDP?
● What is MTU?
● Explain what is a network namespace. Why would someone need to use
it?
● What is DHCP? How it works?
● What is a socket?
● What bonding modes there are?
79. Interview Questions - Commands
● What tools are you using for troubleshooting networking issues?
● How do you change the MTU of a specific interface?
● How to display the ARP cache?
● How to add an ARP entry in the ARP cache?
● How to add a new network namespace?
● How to move an interface from the default network stack to a specific
network namespace
● How traceroute works?
● How to set the speed of a given network interface?
● How to list open connections, sockets in use?
● How to trace all the traffic from a specific host?
● How to change an ARP entry? Is it dangerous?
● How to set a default gateway?
80. Interview Questions - Scenarios
● How to configure statically a newly added interface?
● Can you set MTU for interface configured to work with DHCP?
● How to link two separate namespace so it would be possible to ping an
interface on the second namespace from the first one?
● How to turn your Linux server into a router?
● I’m unable to open more than 1024 remote connections to my application.
Why?
● How to configure network bonding?
● How to troubleshoot why traffic is not reaching its destination? What can
be the possible causes?
82. Next steps in your networking journey
● DHCP
● DNS
● Deep Dive
○ Routing
○ Packet Sniffers
● Iptables
○ Traditionally considered a security subject but has strong
connecting to networking
● Ethical Hacking
○ ARP spoofing
○ Route poisoning
● Open Source Networking Projects
○ Open vSwitch
○ OpenFlow
○ Mininet
○ OpenStack Neutron
85. CREDITS
Special thanks to all the people who made and
released these awesome resources for free:
▪ Presentation template by SlidesCarnival
▪ Photographs by Unsplash
