PIX IP address assignment problem version 6.3(4)

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Oct 16th, 2007
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From which PIX OS version is it possible to assign a /31 address mask to an interface? In version 6.3(4) if I try to assign an IP with subnet mask I get the error:

"Warning : IP and subnetmask form invalid pair indicating broadcast address"

I have seen a /31 mask assigned in PIX OS version 7.0 so I know it is possible. Anyone ever used one in version 6.XX ? I really need to use a /31 address because we have exhausted our company's public IPs.

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acomiskey Wed, 10/17/2007 - 06:28
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What address are you trying to enter?

g.yiannibas Thu, 10/18/2007 - 02:02
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My addressing is:

xxx.xxx.xxx.228 Router

xxx.xxx.xxx.229 PIX

I am aware of the IOS feature being available from version 12.2 onwards. I just could not find any documentation about PIX OS. There is an indirect reference to this limitation in Management Center for Firewalls ver 1.3.2 (part of the CiscoWorks VPN suite):


However the documentation of Management Center for Firewalls itself states that it supports PIX OS versions up to 6.3.3:


So there is no definite answer about versions 6.3.4 and 6.3.5. I already verified that in version 6.3.4 /31 netmasks are not supported so my guess is that most probably they are not supported also in version 6.3.5

Thank you for your help, anyway.


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