Day 67: Syncing between master and slave controllers Part 1

Few assumptions stated in my previous posts have been wrongly assumed.
The assumptions were:
  • The flows installed in the switches are periodically refreshed or re-installed
  • The flows in the switch are retained in the switch as long as it is connected to the controller
After experimenting with the switches, trying to analyze if any timeouts exist on the flows, if the switch configurations are set properly, I realized the following:
  • The flows once installed in the switch remain in it until the switch is turned off
  • The flows remain in the switch even when the controller port is not connected to any controller
So, why did I wrongly make the former assumptions?

It so happens that my Zodiac FX switches (not all of them, few of them) automatically switch off and back on sometimes. And out of these, only few times the switches retain all flows, few other times they lose out on few or all flows. This appears as an error on my controller

DPSET: Multiple connections from <switch-dpid>

This was the reason my flows were not active all the time and lead to my flase assumptions. I've tried to replace the USB cables and ethernet cables that might be responsible for this kind of behaviour. Although the frequency of the error has reduced, it still persists. When I checked online for more info, I must say I was a little relieved as this problem is faced by many people and there exists no definitive fix at this point of time. For now, I shall just treat it as a hardware anomaly and continue with my further experimentation by eliminating all false assumptions I had previously made.

Since my old assumptions do not hold, I need to address one thing:

I had previously decided not to have any syncing feature between controller assuming that whenever a controller takes over, it will install few flows of its own.

In the next post, I shall be addressing the same.

Refer to previous and next posts here.

Author: Shravanya
Co-author: Swati

Comments

Post a Comment

Popular posts from this blog

Day 12: Master Slave SDN Controller Architecture

In the previous post, I was struggling to figure out why all controllers can install flows in all switches irrespective of the code. Well, today the mystery is getting resolved. I found this book that explains beautifully the various roles that a controller can play. The three roles are: Equal : this happens by default all the equal controllers in a network that are connected to the switch can add and delete flows from it Slave: it has a read-only limitation to the switch openflow tables Master: very similar to the switch, but only 1 master can be connected to the switch at that point of time, and no other flows can intercept the communication between switch and master. I highly recommend you go through the above link to get a better picture. Since the default role of any controller is "Equal", we couldn't really differentiate between the three controller flows yesterday. But one good news from this is that we don't really need extensive coding to assi...
Read more

Day 50: Tcpreplay and tcpliveplay approach

Today we shall be exploring how to copy and redirect the OpenFlow packets to more than one controller from the load balancer. The load balancer is anyway sending the OpenFlow packets to one of the slave controllers - c1 or c2. The packets sent to these two controllers needs to be sent to master controller so the master controller can update the new flows added by c1 or c2 on the switches. This ensures synchronization between controllers. There are two implementation methods to achieve the same: Copy all packets generated from the load balancer to the controller side. Only the packets having destination IP address of c1 and c2 can be redirected to the master controller. Thus we can prevent the packets which already are reaching the master controller to be sent as duplicates Copy and redirect packets from the slave controllers - c1 and c2. We need not take care of duplicate packets reaching master controller. This will reduce the time taken to redirect packets. Since the second a...
Read more

Day 1: Understanding Ransomware and how to detect them?

Image
To start this journey, let’s begin at the basics and learn about what ransomwares are, what is the meaning of a ransomware attack, how have other people detected it so far? By learning the above, we will be in a position to analyze any ransomware attack and devise methods to detect, mitigate and prevent them. Definition: Ransomware is a type of malicious software from cryptovirology that threatens to publish the victim's data or perpetually block access to it unless a ransom is paid. To continue understanding and addressing the threats posed by ransomware, let us dig a little deeper. As the definition specifies, ransomware is a type of malicious software. Now, what is a malicious software? Definition: Malware (= Malicious + Software) is a software which is specifically designed to disrupt, damage, or gain authorized access to a computer system. These malwares (or simply dangerous content that can corrupt your system), can enter your system from various s...
Read more