Many-to-many [Synology to Synology] network (offsite) backup

[brickere]

I'm wondering how to manage a situation where there are multiple Synology NAS boxes (varying sizes) that need to backup to other offsite Synology boxes. The sources are in different locations, the destinations are multiple Synology boxes but on the same network (the reason being that one isn't big enough).

I can't figure out how to, for example, use port x for NAS 1,2 and port y for NAS 3 and 4. It seems like Network Backup won't let you modify the port it uses?

Is this a situation where rsync is better/more applicable?

EDIT

Perhaps asked somewhat differently:

Let's say I have two RS3412xs servers (each with their own expansions, so maxed out), and I need to backup multiple offsite Synology boxes of varying sizes to these two RS servers. The issue I have is really one of server architecture. Would I need multiple IP's (one for each of the two RS3412's), or is there some type of internal handling (e.g. a router, etc) that can handle this and point each box to the appropriate RS?

Is there a better place for me to ask these types of questions?

[gabi_cavaller]

Did you every get a reply to this?

[Steph]

I believe this is not possible with Synology products.

I have imagined only one possible solution : have as many public IP address for each Synology NAS. This is what I'm going to do ...

[gabi_cavaller]

I believe this is not possible with Synology products.

I have imagined only one possible solution : have as many public IP address for each Synology NAS. This is what I'm going to do ...

Sorry, don't understand. What is the benefit of providing it with an external IP address in this instance?

[Steph]

Let A1 & A2 be two NASs at your destination site.

Let B and C be two off-sites NAS to backup, at two different sites.

What I planned to do is to have two public ip address at site A. On NAS B, I will specify the first IP address, and on NAS C the 2nd. My router then on site A will know on what NAS he has to redirect the backup depending from what remote IP address the backup comes from.

A bit more clear :-/ ??