What is last hop router and first hop router in Multicast?

What is last hop router and first hop router in Multicast? These are important  terms which are used in Multicast. In this post, I will explain the terms, differences and some detail about this term.

 

In fact, last hop router and the first hop router can be considered as the same thing. But I will suggest a common way of use in this post and will clarify the terms in a most clear explanation.

 

last hop router

Figure – Multicast Last Hop Router and First Hop Router

 

The router which is connected to the Multicast receiver is called Last Hop Router. Almost all Multicast resource will explain you in this way.

The router which is connected to the Multicast source is called First Hop Router. Again, almost all multicast resource would explain the term in this way.

If you are dealing with Local Area Network, you might be calling Last Hop Router (Commonly called as LHR), as First Hop Router and this wouldn’t be wrong. It is all about where you are looking from.

But, I would recommend you to use common definition, which is ‘Last Hop Router’ is the one which is connected to the Multicast Receiver.

Multicast Receiver is connected to Layer 2 switch and runs IGMP and/or MLD to communicate with the LHR, in turns if PIM is enabled in the network, LHR’s job is to generate PIM control plane messages to create a path for multicast traffic and build a multicast routing table among the routers in the network.

 

LHR has many functionality but this is not the scope of this post. In this post, I wanted to just highlight the term, for more Multicast posts, please click here, there are many on the website.

 

Note: Those routing geeks will remember the last mile and the first mile in Access networks. If you are a backbone engineer, connection between user and the operator network is considered last mile, if you are access network engineer, same connection is called first mile.

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