Hi A.Vanson
Some points I consider important:
- It is important you understand every feature configured on the old router and if possible test the funtionality of the same features in the SRX before performing the swap. Having the SRX working in a lab enviroment simulating the production enviroment will give you a very good idea of how the firewall will be working after the change.
- Always have a rollback plan, meaning that if you performed the swap and the SRX is not working as expected you could always replace it with the old router until further testing is done on the SRX.
- You can migrate the router configuration to the SRX, using the old public address, and take advantage of the "replace pattern" command on the SRX to replace the old public addresses with the new ones. Put special attention to NAT/Proxy-ARP configurations, if there are any, because they will be affected the most.
- I am assuming that when you say "split-view DNS" you mean that you host a public facing DNS server that will be contacted also by your internal hosts, always to its public address. Make sure you understand how the SRX needs to be configured in order to have this working. Maybe you need to implement some sort of hairpining NAT? https://kb.juniper.net/InfoCenter/index?page=content&id=KB24639