Loadbalancer – Network Interview QnA

What is iRule in F5 Load balancer

An iRule basically is a script that executes against network traffic passing through an F5 appliance. iRules can write simple, network-aware pieces of code that will manipulate network traffic in a variety of ways. Regardless of whether you’re looking to do some form of custom persistence, setting custom settings for the TCP/UDP protocols or rate-limiting [...]

F5 101 Application Delivery Fundamentals-Study Notes-OSI Layer

Explain, compare, and contrast the OSI layers http://www.tcpipguide.com/free/t_OSIReferenceModelLayers.htm 7 – Application Interacts with the user (FTP/HTTP/SMB/SSH/etc.) 6 – Presentation Converts information into data structures that are understandable by/useful to the system (XML/TLV/JSON) SSL/WEP/WPA 5 – Session Allows two endpoints to exchange data for a period of time. NetBIOS, TCP/IP Sockets, RPCs Not necessarily the length [...]

What is difference between LTM vs GTM

LTM load balances servers as well as does caching , compression, persistence, many more. GTM load-balances data centers. In a normal deployment, a customer will have two data centers, each with GTM and LTM devices. For GTM to work efficiently, customers delegate DNS resolution to GTM. So, a user might just type into their browser [...]

F5 LTM Troubleshooting- Things to check if Pool member is down

Check if the server is reachable from the F5 Load balancer [[email protected]:Active:Standalone] config # ping 172.16.20.10 PING 172.16.20.10 (172.16.20.10) 56(84) bytes of data. 64 bytes from 172.16.20.10: icmp_seq=1 ttl=255 time=3.83 ms 64 bytes from 172.16.20.10: icmp_seq=2 ttl=255 time=2.88 ms ———————————————————— If you want to ping from particular vlan you can specify vlan name after –I [...]

What are the daemons in the F5 LTM? What are there impact if they are not running?

To review logs using tmsh Log in to the BIG-IP command line. Change to the /var/log directory by typing the following command: cd /var/log or cd (go to respective directory of daemon) Use a Linux utility such as cat, or less, to review the desired log file. For example, to view the ltm log file, [...]

F5 troubleshooting using the tcpdump command

The tcpdump utility is a command line packet sniffer with many features and options. For a full description, refer to the tcpdump man pages by typing the following command: man tcpdump Running the tcpdump utility Following are examples of commands used to run the tcpdump utility: Selecting an Interface or VLAN The tcpdump utility’s interface [...]

What is Node and Pool in F5 Load balancer?

Node- A node is a logical object on the load balancer that identifies the IP address of a physical resource on the network.You can explicitly create a node, or you can instruct Local Traffic Manager to automatically create one when you add a pool member to a load balancing pool. You can find out the [...]

Important CLI commands for F5 LTM

TMOS commands run util bash -enable shell show sys self-ip -show self IP’s show ltm persistence persist-records -show persistence records list ltm node [node_address] -show node status modify ltm node [node_address] down -disable node modify ltm node [node_address] up -enable node modify net packet-filter all logging enabled -enable logging for all packet filters delete ltm [...]

BIG-IP F5 LTM Load balancing methods

BIG-IP LTM provides a variety of load balancing methods to choose from. There are two types of load balancing methods. statistic load balancing method / mode. dynamic load balancing mode. 1. statistic load balancing mode:- There are two static load balancing modes. 1.Round robin 2.Ratio 2..Dynamic load balancing mode:- 1.least connections 2.fastest 3.observed 4.predictive 5.dynamic [...]

What is the difference between the F5 LTM vs GTM?

The biggest difference between the GTM and LTM is traffic doesn’t actually flow through the GTM to your servers. The GTM is an intelligent name resolver, intelligently resolving names to IP addresses. Once the GTM provides you with an IP to route to you’re done with the GTM until you ask it to resolve another [...]