Cisco 2900

so I am a total hack on cisco IOS and need to change a fringe router ISP to different IP/SNM/GTW. Below are my givens and my assumed commands. please let me know if I am correct:
Network:       108.188.yx.128
Gateway:       108.188.yx.129
Useable:       108.188.yx.130 thru 108.188.yx.158
Broadcast:       108.188.yx.159
Size:       /27


config t

interface gigabitethernet 0/0
! THE FOLLOWING IS MY BIG ASSUMPTION Doesn't work - get Bad Mask (where do I get this value?)
ip address 108.188.yx.128
no shutdown

interface gigabitethernet 0/1
ip address 108.188.yx.130
no shutdown

#default route
ip route 108.188.yx.129


then I need to write to running/ or boot config correct?

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A subnet mask of gives you 32 addresses per subnet.  The bottom and top addresses are unusable.  That's why you're getting an error.  x.x.x.128 is not a valid interface address when your subnet is

Also, you'll get an error with trying to put two interfaces in the same subnet.  Pick one interface (g0/1 looks like from your example).
It looks like you are wanting to use your G0/0 as the WAN interface, change the ip address to 108.188.yx.130  Make sure this ethernet cable goes to your ISP.

The G0/1 interface could be your internal LAN, and should have the gateway IP your DHCP etc is providing for your internal LAN.  Make sure this cable is going to your internal LAN network.

This will let you statically map IP addresses from your internal LAN to the IP addresses 108.188.yx.131 to 108.188.yx.158 for all of your hosted content/exchange/websites/etc (static NAT).  You will have to also make sure the outside interface G0/0 to your WAN has "ip nat outside", and the internal interface G0/1 has "ip nat inside" for your personal network address translations to work and your LAN clients have access to the internet.

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And then for your last question, yes you need to do a "copy run start" to make sure the commands are persistent through a reboot.
Benjamin Van DitmarsSr Network EngineerCommented:
can you give us youre complete running config. because what does youre router do. is it only nat from external to internal. or is it working as gateway / shaper for youre connection.

what we normaly see. is a small network on the outside interface /30 and a bigger subnet on the local internet side.

if you share youre config we can help you much better
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