Odd routing issue

[Tomasz Konefal]

hello, everyone.

   i've got a funny network layout (it's in transition) and am seeing 
behaviour from FreeBSD 5.2.1 that's different from an Alcatel 6600-24 
and a Nortel 1424T router.  that is, when i use FreeBSD to do my routing 
everything works, but when i use either of the other routers things 
don't work.  there's a VIVID router we're phasing out, see below.  i'll 
outline the network layout below and how things fail on the alcatel and 
the nortel.  when the vivid disappears from the picture our routing 
issues clear up immedeately, but my question is:  does the FreeBSD 
router work in the scenario below because of a bug or because of a feature?

                   +-----------+      +==========+
                   | firewall  |======| INTERNET |
                   | 10.0.1.5  |      +==========+
                   +-----------+
                              |
                              |
                              |            route: 10.0.3.0/24
                              |            next hop: 10.0.2.64
+-------------+   +---------------+     +------------------------+
| 10.0.1.0/24 |---| VIVID router  |-----| Alcatel/Nortel/FreeBSD |<=HERE
+-------------+   | 10.0.1.254    |     | 10.0.1.1     10.0.2.48 |
IP:10.0.1.x       +---------------+     +------------------------+
GW:10.0.1.254     route: default          route: default      |
                   next hop: 10.0.1.1      next hop: 10.0.1.5  |
                                                               |
                                                               |
                                          +----------------------+
                                          | metro network router |
                                          | 10.0.2.64            |
                                          +----------------------+
                                            |
                                          +===============+
                                          | metro network |
					 | 10.0.3.0/24   |
                                          +===============+

   so, the network looks like the diagram above.  putting aside the fact 
that this is a pretty dumb layout, i'm curious why the router point 
labeled "<=HERE" acts the way it does.  when FreeBSD 5.2.1 (haven't 
tried other releases) is doing the routing at that spot all the 
workstations in the 10.0.1.0/24 block can see the internet and the metro 
network and vice versa.  when the alcatel 6600-24 or the nortel 1424T is 
in that place all routing to the internet and to the metro network fails 
even though the routing tables are the same.  can someone shed some 
light on this for me?  is it possible than Spanning Tree Protocol is 
getting involved on the nortel and the alcatel or perhaps some other 
feature?  note, i'm not inquiring on how to fix my network layout, only 
why FreeBSD works in this scenario while other equipment fails.

thanks!
   Tomasz