Modifying Network Packet Buffering in Network Layer

1. Modifying Network Packet Buffering in Network Layer CS518 Final Presentation and Instruction Guide Li Zhang

2. Contents • Notations • Very Brief Introduction • Hardware And Software Preparations • Modifying the Code • Experiments Design • Results and Conclusion • References

3. Background • Five Network Layers in Linux : • MAC and Logical-Link Layer • Network Layer • Transport Layer • Application Layer

4. Traffic Control in Linux and My Goal • In the Linux world, the term traffic control represents all the possibilities to influence incoming and outgoing network traffic in one way or another. • This project focus on modifying the queuing disciplines in network layer in order to create an bigger size buffer which will drop less packets because of time slots used up. • Two reasons to drop packets in network layer: • Buffer overflow. • Policing mechanism detected violation of a rule For example, packet format fault, firewall blocks.

5. Hardware and Software Preparation • Hardware: An x86 networked computer running Windows XP • Software: • VMware • CentOS 5.2 and its applications • linux kernel 2.6.26 • Two tools to monitor network flows: ntop and bing

6. Preparation 1: Create a virtual machine and install CentOS 5.2 • Download VMware Server 1.0.3 from http://www.vmware.com/download/server/ • Install VMware server and register it online. The registration is free. • Create a virtual machine under the guide of video ‘Create_Virtual_ Machine.avi’ • Download and install CentOS 5.2 in the virtual machine from http://img.cs.montana.edu/linux/centos/5.2/isos/i386/

7. Preparation 2: Recompile the Linux kernel • Start Linux and log in as ‘root’ • Download the kernel code and decompressed it into /usr/src $ cd /tmp $ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.26.tar.bz2 $ tar -xjvf linux-2.6.25.tar.bz2 -C /usr/src $ cd /usr/src/linux-2.6.26 • Install gcc, a C compiler $ yum install gcc • Configure the kernel, do not change anything, just select ‘exit’ $ make menuconfig • Make and install modules and kernel $ make $ make modules $ make modules_install $ make install

8. Preparation 2-continue • Create an initrd image which contains device drivers which needed to loaded $ cd /boot $ mkinitrd -o initrd.img-2.6.26 2.6.26 • Modify the grub file • Open /boot/grub/menu.lst with text editor • Modify the default booting kernel pointing to 2.6.26 • If there is a line like this ‘menu hidden’, delete the whole line • Restart Linux • Select the kernel 2.6.26 from the boot loader menu

9. Preparation 3: Install ntop and bing • Step 1：Download and install rpmforge-release $ wget http://dag.wieers.com/rpm/packages/rpmforge-release/rpmforge-release-0.3.6-1.el5.rf.i386.rpm $ rpm -Uvh rpmforge-release-0.3.6-1.el5.rf.i386.rpm • Step 2: Intsall ntop $yum install rrdtool $yum install ntop • Step 3: Install bing $yum install bing

10. Preparation 4: Duplicate Virtual Machine • A virtual machine can be duplicated very easily. • Duplicate the file folder you created in Preparation 1 and rename it as Linux-modify • Use VMware to open the .vmx file in the file folder Linux-modify. • Select ‘Edit virtual machine setting’ and rename the new machine as ‘Linux-modify’ • Only modify the kernel in the new machine.

11. Modify the code • First double the buffer size by editing the function tbf_change() in netsched/sch_tbf.c. The variable max_size is the max buffer size. • The watchdog() function is invoked when the timer for a packet expires. This function will be used in tbf_dequeue() to determine whether the process of transmitting a packet should be interrupted. Modify the condition to invoke the watchdog().

12. Recompile again • $ cd /usr/src/linux-2.6.26 • $ make menuconfig • Select ‘General setup---’ • Select ‘Local version-append to kernel release’ • Enter a name you want, press ‘OK’ • ‘Exit’ twice • Watch video ‘recompile_again_menuconfig.avi’ • Then follow the steps after ‘make menuconfig’ described in Preparation 2. Remember using the version name you created. • Restart and select the kernel 2.6.26_with_your_name from the boot loader menu

13. Experiments • Using bing which is a tool to identify the bandwidth currently available between two computers. • Get local host IP address: $ ifconfig • Use bing to test the bandwidth betwwen the local host and www.joyo.com $ bing –e 50 –i 1 –s 100 –S 1200 Your_Local_IP www.joyo.com • Using ntop to monitor the network in the long term • Start ntop and keep the terminal running ntop open $ ntop • Open a web browserr, for example Firefox Visit http://localhost:3000/ • Watch video ntop_and_bing.avi

14. Results

15. Results-continue

16. References • K. Wehrle, F. Pahlke, H. Ritter, D. Muller and M. Bechler, ‘The Linux Networking architecture’, Pearson Education Inc, 2005 • http://www.cndev.org/forum/msg.aspx?pid=22736 • https://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.2/pdf/Deployment_Guide/Deployment_Guide.pdf • http://gzmaster.blog.51cto.com/299556/77883 • http://www.cyberciti.biz/tips/compiling-linux-kernel-26.html

17. The End Thank you!