Assistance with Cisco 1721 and Point-to-Point T1 2

[batocaster]

I have two Cisco 1721’s with WIC 1DSU-T1 V2 modules that will be connecting a leased, point-to-point T1 between two buildings on the same campus. The networks are both NAT with very generous subnets. Both 1721 routers are behind our main router which connects us to the Internet and both 1721’s will be used only to connect the remote building to the main location. They will not connect directly to the Internet. The routers and T1 are replacing a bridged wireless solution which currnetly connects the offices.

I am a newby when it comes to routing and would greatly appreciate any assistance on my as of yet untested configuration. Cisco manuals indicate that directly connected routers do not need static or dynamic routing enabled. Are the 1721’s considered directly connected when they are seperated only by the T1 circuit? If routing is required, am I best to use a static route? Also, do the T1 WICs require clocking to be set on the serial interface? Some sources indicate it to be handled automatically and some indicate that you need to set one end to “clock source internal” and the other to “clock source line” as in the configuration. Any help and any additional comments on my configuration are appreciated. I am new to this and think I might be close to my solution but am a little lost. Thanks in advance!

Router A:
ip subnet-zero
!
interface FastEthernet0
ip address 10.147.0.254 255.255.0.0
speed auto
full-duplex
!
interface Serial0
ip unnumbered FastEthernet0
no fair-queue
service-module t1 clock source internal
!
ip classless
no ip http server


Router B:
ip subnet-zero
!
interface FastEthernet0
ip address 10.101.0.254 255.255.0.0
speed auto
full-duplex
!
interface Serial0
ip unnumbered FastEthernet0
no fair-queue
service-module t1 clock source line
!
ip classless
no ip http server

 

[idontread]

Hope i am not screwing this one up

batocaster>

IF the p-2-p T1 is provided by the ILEC /Telco company, then try to default setting of the csu/wic (clock line) on both routers. if its just two routers, using static route should be fine. on the serail interfaces, connect them via another ip network like router A 172.16.31.1 mask 255.255.255.252 and router B 172.16.31.2 mask 255.255.252 and that should creat a p2p ip network. since these routers are talking only to each other, so as said before, just setup a default static route (like on router A, ip route 0.0.0.0 0.0.0.0 s0)

I cant think of anything else right now so give that a try and see if works.

 

[batocaster]

idontread,

Thank you for the response. I will set the IP on each of the serial interfaces and add the static routes. I am curious…when using a default static route (ip route 0.0.0.0 0.0.0.0 s0) are specific IP addresses required on the serial interface? The “ip unnumbered” command sets the interface to use the fast ethernet interface IP. Since the default static route would point to the s0 interface and not a specific IP address, would it be acceptable to use the “ip unnumbered” command?

Another reason I’m using “ip unnumbered” is because I don’t have a specific IP range assigned to the T1 by the telco. Hopefully this doesn’t sound completely stupid but if I do address the serial port of each router connecting to the T1, can I simply “make up” IP addresses using NAT? For example 10.10.10.1 and 10.10.10.2 or the 172.16 #'s that you suggested? Are there implications with doing this? Do I need to stay in the same context as the rest of my network or do I simply need any old IP addresses for the serial ports?

Thanks for any additional assistance!

 

[IllegalOperation]

I never use IP unnumbered. If that lone IP address goes down, then you have no way of accessing the router remotely to troubleshoot. You can use IP unnumbered in your scenario, but why not just throw a /30 on each serial interface instead?

For point to point circuits, you do not get assigned a registered IP block from your provider. You can "make up" your own address scheme. Another words, assign the serial interfaces a private address range (10.x.x.x, 172.16.x.x will work for example).

You do not need to stay in the same context with your network when assigning addresses to your serial interfaces. As a matter of fact, I think it is easier to administratively manage your addresses if they utilize different subnets. Especially when you grow into a larger network, that requires multiple point to point links. You can assign the interfaces on those links the 192.168.1.x range, for example. Just make sure your routing tables are correct. Always plan for the future.

Hope that helps....

 

[batocaster]

Thank you both very much for the assistance. My questions have been answered and it is much appreciated!