about rule in FWSM

mylove142 · ‎10-16-2007

Hi all,

I confuse about configuring rule in FWSM,

I use Catalyst 6513 + FWSM, I configure one rule:

Source Dest Service

10.20.4.0/27 any IP

that means I have 32 address from 1 to 32 to connect to any with service IP. But when I test, I only configure from 1 to 31, IP 32 can't connnect to any. If you know why, please answer me early.

Thank you very much.

Regards,

Jon Marshall · ‎10-16-2007

Hi

This is because .32 is not part of your 10.20.4.0/27 subnet. Think of it like this.

/27 = 255.255.255.224

256 - 224 = 32 so your subnets go up in 32's eg.

Ist subnet = 10.20.4.0 255.255.255.224

2nd subnet = 10.20.4.32 255.255.255.224

3rd subnet = 10.20.4.64 255.255.255.224

etc...

So .32 is the network address of the next subnet.

Just for completeness you shouldn't really use .31 as an IP address of a host either as this is the broadcast address for the 10.20.4.0/27 subnet.

HTH

Jon