BIER is Bit Indexed Explicit Replication which is the newest proposal for IP Multicast.
Although I say IP Multicast, of course, it works on MPLS networks as well.
You can take our IP and MPLS Multicast Training for more detail.
BIER works by assigning every edge device a Bit Mask position.
Then, instead of sending Multicast packet to each destination IP address (Receiver IP address), basically, it sets the Bit positions and saves the amount of data plane state.
It uses Unicast transport as underlay reachability, and Bit Mask is advertised through the IGP control plane.
So, OSPF and IS-IS newly assigned TLVs to handle the BitMask to Edge device (BFER - Bit Forwarding Edge Router in BIER terminology) assignment and distribution.
It is in theory can be used not only for multicast but also for Unicast traffic as well.
When we use it, we don't need to have mLDP, RSVP P2MP LSPs, or PIM in the Core Network (Of course at the Edge, you can still have towards the customer in mVPN scenarios).
So basically, by removing those protocols from the network, in theory, the simpler network design you should have. I am saying in theory, because having less protocol doesn't always mean, having a simpler design.
Because we would be throwing the complexity to the protocol in this case. So carrying Bit mask positions in OSPF and IS-IS makes these protocols codes more complex. So, there is no free lunch in network design.
I recorded a very long, detailed video about BIER with the two guys who actively participated for the invention of this protocol. Tony P has been there since day 1 of this protocol and hopes you will find our video useful if you are reading this post.
In this video, Orhan Ergun, Dr. Tony Przygienda, and Jeff Tantsura discuss a pretty new Multicast Architecture - BIER. BIER is radically different than traditional Multicast.
BIER uses unicast transport to provide Multicast without Ingress Replication! - So Scalable. (It keeps state at the Edge too, not in the Core as traditional GRE, mLDP or RSVP solutions in the Core)
Scalability, Simplicity, Agility, are the pros of BIER, lack of large-scale deployments, hardware change/Silicon Support current disadvantages. But many Core networks are considering it and I want my followers to be aware of BIER!