Point to point WAN addressing (IP's) ????????????

[pbxphoneman]

I have a t1 between two buildings and want to use it just for joining a single stand alone computer to the main network.I own the routers and the cable...no wan provider.
question...
each router has it's own Ethernet address, but routers are asking me for either numbered (static) or unnumbered WAN addressing scheme .I have no need for RIP with this setup. I'm guessing that if I was using this setup through a WAN provider,they would tell me these static numbers..correct? should I be using unumbered WAN scheme..if not..what kind of IP addresses can I put in there
for my WAN?
thanks for any hints

 

[svermill]

Yes, your service provider would likely provide you with IPs on a public network. Since you own the connectivity, use any address scheme you like. Typically a /30 networks are used on WANs these days. This equates to a 4-address network. The first IP is the network address, the last is the broadcast address, and the middle two are the serial p-t-p interface IPs. I understand that Cisco is now supporting /31 addresses, but I haven't read up on it in any detail.

As a matter of good practice, you should map out your IP scheme carfully. Growth eventually comes whether or not you expect it. Too many options out there to discuss it all here.

Finally, IP unnumbered just borrows your ethernet IP and reuses it on the serial side. I don't like it, but it works just fine for lots of folks.

 

[pbxphoneman]

the WAN IP addressing numbering is the problem I'm having.Can I use any old number or is there a desirable range of IP's that I should be using for my static WAN route?Some one told me also that I have to have 3 defined networks in order for the router to work...LAN A, WAN link & LAN B.

thanks

 

[svermill]

What you were told was true unless you use IP unnumbered. You can read all about the actual mechanics of IP unnumbered at

http://www.cisco.com.

I personally would choose to use actual IPs on the WAN.

One example would be to choose the private IP network of 192.168.100.0/24 for all of your WAN links. Subnet this subnet into /30 networks. Here are a few examples:

192.168.100.0/30: Network address
192.168.100.1/30: IP address of one side of a serial link
192.168.100.2/30: IP of the other side of a serial link
192.168.100.3/30: Broadcast address

192.168.100.5/30: Network address
192.168.100.6/30: IP address of one side of a serial link
192.168.100.7/30: IP of the other side of a serial link
192.168.100.8/30: Broadcast address

/30 by the way is 255.255.255.252

Of course, it's important that you choose a range of IPs that won't overlap with anything else in your network. Am I answering your question or am I still missing the point?

 

[pbxphoneman]

I am new to the /30 subnet mask. Is it used to break it down into smaller networks? 255.255.255.0 (class C) seems to be the default on alot of my router masks when I input some of these IP (ether & WAN) addresses.I'm hitting the books on this stuff as I try to get this thing flying..and learning on the fly...thank you for all your input!

 

[svermill]

Yes, it's used to break down larger networks - not just class C, but any network. The further to the right you move that mask, the smaller the number of usable IPs and the greater the number of subnets. No sense in wasting 252 usable IPs on a serial point-to-point connection.

I guess Cisco and possibly some other vendors are building some new intelligence into their boxes. I'm told that a /31 mask is now possible. The router must assume that a p-t-p network is present when configured with a /31 mask. There are only two IPs in a /31, so the router must know not to bother with broadcast or network IPs. What good would either of those do in a p-t-p environment anyway? Makes good sense.

 

[pbxphoneman]

I think my main trouble right now is getting to know the software for the router (Intel er8220) where to input the values.
At this momment I'm able to telnet into the end routers WAN IP address but not the Ethernet address of it..ping doesn't work either,I suppose it won't either.reply from my router eth IP =(destination net not reachable) but the WAN ip of the end router is good.
I have a feeling I'm leaving out so kind of static route for this on my end,just hard finding where to do this,lol.
thanks for all the info!!!

 

[svermill]

Yes, the router that you are telnetting from need a route to the ethernet network. It doesn't need a route for the WAN IP because it has its own interface attached to that networks. So it knows where that is. I'm not familiar with your router though, so I can't be of much help in that regard...