Two Consoles, can't connect as Multi-Console setup... Yet another network config problem?

So I was having fierce trouble the other day getting two consoles to network together. I thought I had covered all the normal simple mistakes and oversights but couldn't get them to cooperate.

A friend brought in his ion (classic, but the newer non-XP variant) to program a show in a venue that has an old element 40/250

The idea was that during tech we could Master/Client these two together so that the op position in the box could be set up with the dmx out and midi i/o, and that he would be sitting out in the stalls programming on his ion.

We tried both with a router in the middle which is used as an AP for iRFR, and with just a straight connection between the two consoles. We tried switching which one we wanted to be the master. We tried both network ports on the ion. We tried giving them IPs and DHCP assigned IPs.

In all cases we could get both desks being able to ping each other, but never see each other when searching for master consoles.

Both consoles are on the same version and build

Ion ip

element ip

both subnet mask

both default gateway

Thanks for any helpful suggestions you can think of. I'm already bracing myself for the reply that asks if i checked that one really simple and obvious thing..