Put F5 in the network as inline router running OSPF and LB HTTP traffic toward cache machines

Hi JJ

This is very much possible, even if you place your F5 inline. Since you're on ISP backbone, I would suggest to carefully select high end F5 LTM platforms to handle huge traffic volumes. Such as the VIPRION platform. In order to use OSPF (or any dynamic protocol), you need to buy ARM license (Advanced Routing Module) from F5. Refer to this link:-

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos-ip-routing-administration-11-2-0/4.html

Now for the LTM part, you have to use two types of virtual servers. First, an IP forwarding virtual server (L3), so as to forward default traffic towards your upstream routers. Second is your http (port 80) virtual server, which will intercept all traffic to Internet on port 80 and re-direct this to your pool of caching servers, for load balancing. Also, your cache servers should again point back to the F5 and use L3 IP forwarding virtual server to reach the Internet.

https://support.f5.com/kb/en-us/solutions/public/7000/500/sol7595.html

It is somewhat similar to a PBR on the F5 LTM. See this below link:-

https://devcentral.f5.com/questions/how-to-config-pbr

Cheers

Sumanta.