Technical Blog: September 2016

src: https://worldtechit.com/gtm-vs-ltm-difference-f5-global-local-traffic-manager/

GTM – Global Traffic Manager Overview

The Global Traffic Manager, aka GTM, is one of the cutting edge modules offered on F5 Networks BiG-IP platform. “GLobal” is the right word for this module because it has the ability to make load balancing decisions for systems all over the US and the World. You can think of the GTM as an intelligent DNS that is security minded. In other words its logic can make informed decisions on correlating a hostname to an IP address while keeping security in check.

Most things you do on the Internet or Private networks start with name resolution – so it makes sense if you’re going to load balance an application it would start at this layer – resolving names to IPs based on availability, Performance, and even Persistence. It’s important to note, traffic does not “route” through the GTM, the GTM simply tells you the best IP to route to based on metrics for the URL in question. That IP can be almost anything really, but usually it’s an actual server, or a virtual IP that fronts multiple servers. Like a traditional DNS architecture you usually have multiple GTMs in your architecture, this is for redundancy/availability.

The main configuration element in a GTM is called a Wide IP or WIP for short, or as my significant other likes to call it a “Wipey” ;). There are many configuration elements that work in concert with a WIP, but at the base of it all is the Wide IP. A WIP equates to the common URL you’re load balancing, for example www.yourcompany.com. A pool or pools are usually attached to a WIP which contain the IPs it’s intelligently resolving. Like your run of the mill DNS server, the GTM does not tell the requester any information about ports. Though, the monitors associated with the pool members can indeed monitor availability or performance on ports.

LTM – Local Traffic Manager Overview

The Local Traffic Manager, aka LTM, is the most popular module offered on F5 Networks BiG-IP platform. The real power of the LTM is it’s a Full Proxy, allowing you to augment client and server side connections. All while making informed load balancing decisions on availability, performance, and persistence. “Local” in the name is important, opposed to the GTM, traffic actually flows through the LTM to the servers it balances traffic to. Usually the servers it’s load balancing sit “locally” in the same data center as the LTM, though that is not a requirement. With SNAT configured on the VIP, if you can route to it you can load balance it – so it’s possible to have servers in different data centers be a part of the same pool in an LTM VIP.

The main configuration element on an LTM is the Virtual IP or VIP for short. There are a plethora of configuration elements that work with VIPs, but at the heart of the technology it’s a VIP they are all a part of. Like a WIP, VIPs equate to the URL you’re load balancing, but at its lowest level. Like a WIP it usually contains a pool with the servers it’s load balancing & monitor(s) to measure availability / performance.

Some of the Key differences of the GTM vs LTM

The biggest difference between the GTM and LTM, as mentioned earlier, 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 name for you.
Similar to a usual DNS server, the GTM does not provide any port information in its resolution.
The LTM doesn’t do any name resolution and assumes a DNS decision has already been made.
When traffic is directed to the LTM traffic flows directly through its’ full proxy architecture to the servers it’s load balancing.
Since the LTM is a full proxy it’s easy for it to listen on one port but direct traffic to multiple hosts listening on any port specified.

How do the GTM & LTM work together?

The GTM and LTM can work together or they can be totally independent. If your organization owns both modules it’s usually using them together, and that’s where the real power comes in.. They do this via a proprietary protocol called iQuery. iQuery, functioning on TCP port 4353, reports VIP availability / performance back to the GTMs. The GTMs can then dynamically resolve VIPs that live on an LTM(s).

When a GTM has LTMs as servers in its’ configuration there is no need to monitor the actual VIP(s) with application monitors, as the LTM is doing that & iQuery reports the information back to the GTM.

The Internet Protocol and other network addressing systems recognize five main addressing methodologies:

Anycast addressing uses a one-to-nearest association; datagrams are routed to a single member of a group of potential receivers that are all identified by the same destination address.
Broadcast addressing uses a one-to-many association; datagrams are routed from a single sender to multiple endpoints simultaneously in a single transmission. The network automatically replicates datagrams as needed for all network segments (links) that contain an eligible receiver.
Multicast addressing uses a one-to-unique many association; datagrams are routed from a single sender to multiple selected endpoints simultaneously in a single transmission.
Unicast addressing uses a one-to-one association between destination address and network endpoint: each destination address uniquely identifies a single receiver endpoint.
Geocast refers to the delivery of information to a group of destinations in a network identified by their geographical locations. It is a specialized form of Multicastaddressing used by some routing protocols for mobile ad hoc networks.