Error on restarting networking :SIOCSIFFLAGS

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http://askubuntu.com – I have a sever with 2 network cards, an internal IP on one card (eth0) and external IPs (aliased) on the other card (eth1). I lost connection the public network and I tried to restart networking with /etc/init.d/networking restart and got the error "SIOCSIFFLAGS: cannot assing requested IP and Failed to bring up eth1". I even added the IPs in the interfaces file but still got an error on restarting. I could not ping my default gateway. A work around was to add ifconfig eth 0 x.x.x.x route -add default gw x.x.x.z I could then connect to the public network. What could be the issue here? (HowTos)