Not able to assign correct mask on outside interface for Cisco PIX-515E firewall

We recently changed our ISP and were given a public address with a /29 mask to use.
When I put in the  address and try to assign as the mask I immediately get an error Bad mask. I can, however, use the next ip adddress (part of the 6 useable ones) with that mask. The version of PIX is 7.2(2)
Thanks in advance for your help!
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Pete LongConnect With a Mentor Technical ConsultantCommented:
with a .248 mask you only get 6 usable IP addresses
Pete LongTechnical ConsultantCommented:
What IP address are you using? is it the broadcast or network address for your new subnet?
dcosentiAuthor Commented:
We're trying to use the network address for the interface. We originally had a Juniper netscreen that got hit with some power surge and we lost the power supply. A new one is on order. For now we're trying to use the original PIX in it's place. Maybe Juniper is more forgiving when it comes to assiging ip addresses to interfaces. We've asked our ISP to change their route to this other address instead of the one we were using. Hopefully this will work.  Thanks again
Pete LongTechnical ConsultantCommented:
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