how does my provider route to me

[carl_townshend]

Hi all my service provider has a router and pix on my site, the router connects to the internet via a serial, the pix and router are on the same network, would the router be using ip unnumbered on the serial interface ? and also we have been assigned ip addresses using a x.x.255.x network, how come we can use the 255 network ?

[gpulos]

it is unlikely that the ISP router at your site is using ip unnumbered.

(i've never seen this from an ISP providing CPE; but i have not seen it all in my 20 years of networking)

as far as 'how come we can use the 255 network' this would be because it is legal to do so.

since you have not provided the subnetMask, i cannot tell you exactly how it works out to be that it is a usable network.

please don't confuse a broadcast address of 172.16.255.255 /24 with a valid host address of 172.16.255.X /24.

255s are allowed to be used in subnet IDs as long as they aren't the broadcast address for the subnet ID in question.

(as in the example above)

please see the following link for IP Addressing & Subnetting:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml

[carl_townshend]

hi there

we have a cisco 1700 and pix from our provider, the router connects to the isp via serial, the ethernet connects straight to the back of the pix interface, yet the pix and router both have public ip's, we can ping both, would the routers serial have another address and they just forward that range to the serial address of the router ?

[mrmozaffari]

Hi

I think you want to know how your provider route subnet to you.

it seems you unnumbered you serial interface to your ethernet so the serial interface uses the ethernet ip address.

at the service provider they can define a loopback interface with another ip address out of your range and unnumbered their serial interface to it ,only thing that they need is an "ip route" the configuration at service provider should like this :

NOTE ALL THIS STATEMENTs NOT REAL AND It s ONLY AN EXAMPLE

interface loopback 0

ip add 200.1.1.1 255.255.255.255

interface serial 1

ip unnumbered loopback 0

//this the interface that connect directly to you//

ip route (your network address) (mask) serial 1

like :

ip route 20.1.1.0 255.255.255.0 serial 1

in this sample 20.1.1.0 is your network range.

so you can have all of 255 ip address by assigning the ip address to your ethernet or fast ethernet and then unnumbered your serial to them.

Thanks.

hope usefull.