what does ar serial int and cr serial int stand for in a ppp connection

I was wondering what the "AR serial int" and "CR serial int" stand for in the setup directions for a ppp T1 connection. I realize that they are the IP addresses of the serial interfaces on the router at the client site and ISP site, but I am wondering what they stand for.

What do these abbreviations stand for?

Also I was wondering about the IP addresses that I was assinged. I was given a 255.255.255.252 mask. I have .248 for the WAN link IP,  .249 for the AR serial int ip, and .250 for the CR serial int ip. With this subnet mask, how is it that the .248 can be used as an IP, shouldnt it be the subnet ID? And is .251 used as the broadcast address?
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ryan80Asked:
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NetEngineerFoxConnect With a Mentor Commented:
nnnnnnnn.nnnnnnnn.nnnnnnnn.nnnnnnhh
IP      Mask      Notes ...
192.168.254.248      255.255.255.252      Subnet Address
192.168.254.249      255.255.255.252      
192.168.254.250      255.255.255.252      
192.168.254.251      255.255.255.252      Broadcast Address

If you have a 252, then what you say is correct. (used 192.168.254.X as an example)

AR is usually "Access router, or edge router"
CR is usually "customer router"

Though I am not 100% on how it applies in the command AR/CR serial int.
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ryan80Author Commented:
WAN Link IP Address:**.***.***.248
AR Serial INT IP Address:**.***.***.249
CR Serial INT IP Address:**.***.***.250
WAN Link Subnet Mask:255.255.255.252

This is what we were given for our T1 connection. I thought that since it was a .252 mask that only .249 and .250 were usable. Or am I incorrect and .248 is usable as well?

 I think there is a command that makes the subnet and broadcast address usable? Is this what has to be done?
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NetEngineerFoxCommented:
What you are thinking of is "ip subnet zero" (which is now default on most network devices).

What they gave you is valid.  The "WAN link IP address" just identifies the subnet or network you have to work with.
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Don JohnstonInstructorCommented:
.248 is the address of the network.

While I can't for the life of me remember what AR and CR stand for, I do know that CR is the customer side of the link (Customer Router?). So the serial interface of that device would get the .249 address.

AR would be the provider or other end of the link and would get the .250 address.

 
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ryan80Author Commented:
I think that I was thinking of the command "no ip directed-broadcast" for a point to point link.

So in this case, is the CR IP address the one that I will be NATing, the .248 is the subnet address, and the AR IP address is the other end at the ISP?
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Don JohnstonConnect With a Mentor InstructorCommented:
Unless you're running pre 12.0 code, "no ip directed-broadcast" is default.

>So in this case, is the CR IP address the one that I will be NATing, the  .248 is the subnet address, and the AR IP address is the other end at  the ISP?

NATing? If you are going to be doing NAT and this link goes to an ISP, then yes.
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ryan80Author Commented:
Thanks for the help.

So you could use a /31 prefix for a point to point link then with any version after 12.0?
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