If you are replacing one technology with the other, these questions you should be asking. This may not be the complete list and one is maybe more important than the other for your network , but definitely keep in mind or come back to this post and check before you replace one technology with another one !
Is this change really needed ? Is there a valid business case ?
First and most important question, because we are deciding whether this change is absolutely necessary. If the technology which you will migrate won't bring any business benefit (OPEX, CAPEX , New Revenue Stream etc.) then existing technology should stay. This is true for the new software release on the routers as well.
If there is no new feature which you need to use with the new software release and if there is no known bug that effects the stability of the network, having a longer software lifecycle is better than upgrading the software frequently.
What is the potential impact to overall network ?
New technology might require extra resource usage on the network. Can your network devices accommodate this resource usage growth ? Opposite is true as well. New technology might reduce the resource usage but at what cost ? In general , reducing the state in the network (Routing table , MAC address table , MPLS Label table etc.) creates suboptimal routing and black holing depends on the network topology.
For example, if you replace your full mesh IBGP design to IBGP Route Reflector design, it reduces the overall resource usage on the network (Reduces the state on the routers) but creates suboptimal routing (Depends on the topology)
What will be the migration steps ?
In network design lifecycle , deployment steps are prepared by the designers. These steps are covered in Network Migration Plan document , if separate migration document is not asked by the customer , then in the Low Level Design document (LLD) , these steps are highlighted clearly.
If migration steps is not executed in an order, you have longer network down time which cost money to the organization. Or migration operation completely might fail. In any migration document , rollback plan should be included too. So , if the migration can not be executed in a planned time, escape plan , rollback plan should be started as planned earlier.
Is there a budget constraint ?
Budget is always a real concern. Almost in any business. Why budget is important in technology migration ? Because new technology may not be known by the network engineers , and learning process might be necessary. Free learning resources are good but how much you can trust ?
So, I always recommend people to take training in a structured way from a known network designers who follow the most recent updates in the industry , designed many networks from any scale (not just couple large scale) , recommended by the people who you trust in the industry. ( I spend time to write, let me do a little marketing ? ) Budget is a concern when you try to design large scale network , adding a new technology to the existing (brown field) network , merging and acquisition design , securing the network etc.
When you migrate , ask yourself , do my network engineers in the company know/handle the new technology ? Do you need to buy additional hardware to accommodate the new technology ? I can expand this list. Let me know your comment in the comment box below. Did you recently migrate any technology in your network ? Would this post be helpful ?