asterisk users - Jul 2007 - SIP peer unrechable when using an aliased interface

Hi,

I'm experiencing a strange behavior on one of my asterisk servers.

When I make a sip connection (sip.conf) between the 2 boxes using the
primary interface it works fine.

When however use an aliased interface (ethX:Y) it fails.

from sip show peers:
ast-rem-vpn       192.168.3.253            A  5060    UNREACHABLE

when I use the ethX interface directly, it works fine.

Did anyone experience such a strange behavior ?

Thanks

Laurent