My eth1 is crazy

Hi all, i'm having an issue with my bridge. I have the following network:

ADSL router (192.168.0.1) ------ [eth0] Bridge (192.168.0.2) [eth1] ------- Workstation (192.168.0.3)

Bridge works, but after some minutes, my eth1 card (8139too driver) goes link down and link up, disabling access to the bridge IP for a while (bridge functionality for workstation works ok). This happens between several minutes all the day. I've readed that some NICs have problems working in promisc mode.

Is my realtek sucking or what's happening?
Thanks.