Thank you for the excellent explanation. I apprecitate you taking the time to write all of this down.
There’s one significant question that I have about DMVPN in general and that is… where should the summarization be performed?
I mean, there appear to be various ways to perform it. We could create a single big summary route on the hub, which would summarize the networks advertised by the spokes, we could create a separate summary route on each spoke and have them advertised to the hub plus not to mention how different it would be with each protocol (EIGRP, OSPF, BGP).
You’re right that there are multiple ways to perform summarization in a DMVPN network and it can indeed vary based on the routing protocol in use.
In most cases, summarization is performed at the hub. This is primarily because the hub is the central point of the network and has full visibility of all the routes from the spokes. Summarizing at the hub can help to reduce the size of the routing table on the hub router and also limit the propagation of unnecessary routing information to the spokes.
However, there are situations where summarization might be performed at the spokes. For instance, if a spoke is connected to multiple networks and only wants to advertise a summary of these networks to the hub, it could perform summarization. This can help to reduce the size of the routing table on the hub and other spokes.
Regarding the routing protocol, each has its own characteristics and methods for summarization:
EIGRP allows for summarization at any point in the network, which provides more flexibility. * * * OSPF allows summarization only at ABRs and ASBRs.
BGP typically performs summarization at the edge of the network, which can help to limit the propagation of routing information.
In the end, the choice of where to perform summarization will depend on the specific requirements of your network, including the routing protocol in use, the size and complexity of the network, and the desired level of control over routing information.
