BGP | avoid loops with redundant gateway

[omz]

Hi all

I have a requirement..  "any prefix that originated in any of site will not advertise back to the same site via a redundant gateway"

The sites are multihomed same BGP AS across 4 sites .. 2 CEs connected to 2 PEs .. and there is iBGP between the CEs.. 

The PEs do as-override .. do the PE's need to do SoO as well? Or as-override is enough?

If the PEs didn't do as-override .. CE's will need allowas-in .. correct?

How to check there are no loops i.e CE routes are not advertised back to the other CE in the same site?

What show commands or debugs can I use to check this?

Thank you

[shaps]

You can use allow as in or as overide, on the CE or PE respectively.

If I understand your query about the loop within the site with the two CEs then this shouldnt be an issue as ibgp vs ebgp with regards to routing should overcome this;

You want both CEs to be able to have visibilty of the customer subnets via each other.