wildcard mask question

^ This means bits 3 & 4 are sat, e.g.

In theory this byte could then have the following values: 128 64 32 16 8 4 2 1 1 0 0 0 0 1 1 0 => 134 1 0 0 0 1 1 1 0 => 142 1 0 0 1 0 1 1 0 => 150 1 0 0 1 1 1 1 0 => 158 ^ ^

But with network devices such a construct seems to be illegal. To my knowledge you are not allowed to have variable bits somewhere in the middle.

I don't think so.

Regards, Christoph Gartmann

Non-continous netmasks are somewhat unusual, but legal in nearly every sense. They are especially useful in access-lists (unfortunly not available on PIX).

Ok, I tried to use them with several different devices and most of them didn't like/honor them.

Regards, Christoph Gartmann

I agree. The wildcard masks are not valid to determine the host range for the subnet.

Such netmasks are usually ignored by the device developers. Doesn't matter.

Yes, you can determine the valid host range. it just not straight forward as contigiuous subnet masks. Consider 10.11.120.221 0.0.0.120:

The net mask would be 255.255.255.135. If we ignore the first 3 octets, we have

host: 11011101 mask: 10000111 network: 10000101 --> 10.11.120.133 host 1 : 10001101 --> 10.11.120.141 ^^^^^ cycle the 4 zero bits in the mask through all posible values

host 14: 11110101 --> 10.11.120.245 broadcast: 11111101 --> 10.11.120.253

Convoluted but valid.