[c-nsp] Re: 7206VXR for DSL Termination

[Roger Weeks]

We provide DSL termination on our 7206VXR with an NPE300 (256M) and a  
PA-A3-T3 DS3 card.

Our setup is a little different in that we're not taking the ATM from  
a switch but directly from the Nortel ATM equipment that SBC  
provides, so I can't answer anything about the OC3 card setup.

We handle 500+ VCs on this unit with no problems at all, and will be  
adding around 300 more in the near future.  Previous replies on this  
list have indicated that a 7206VXR should be able to handle 3-4000 VCs.

You have a couple of options to set up static configs.  I don't use  
auto build pvcs because it doesn't really work with the way SBC  
provisions DSL lines.  If your LEC provides you with a range of VPI/ 
VCI upfront, then auto build pvcs work fine.  We don't know what VPI/ 
VCI SBC will give to any particular customer ahead of time, so  
frequently we get a mixed bag of non-contiguous numbers.

We started out by using PVC ranges and mostly DHCP addressing, so the  
interface config looked something like this:

	int atm2/0.434 point-to-point
	ip unnumbered Loopbackx
	ip helper-address x.x.x.x
  	no ip unreachables
  	ip flow ingress
  	no ip route-cache
  	no ip mroute-cache
  	atm route-bridged ip
	range pvc 4/34 4/55
		class-range classADSL

	vc-class atm classADSL
	  ubr 6216
   	  encapsulation aal5snap

You can specify different vc-classes with different settings, this  
one is obviously for 6mb DSL customers.

After a while, however, the ranges get broken up because we have  
static IP customers also, so the ranges get fragmented.  Just  
recently we converted to having a single configuration for each PVC,  
because the ranges are too difficult to manage with our number of  
circuits.

Either of these setups mirror your redback setup, route-bridged 1483  
with private ARPs, it's not a shared network between DSL users.

One thing you will run into eventually when you have enough circuits,  
especially if you use single configs for each PVC, is that the NVRAM  
on your 7206 is too small to hold your config.  You'll need to store  
the startup-config elsewhere:
		boot config disk0:startup-config
This writes a flag into nvram telling it to look on disk0: for the  
startup config.  After you run this command (and also put it in your  
startup config), a dir nvram: will show that your large startup  
config is in nvram, but it really gets loaded from the other location.

With regards to IOS version, I finally ended up on 12.3T.  Initially  
I went with 12.2.25S on the recommendation of another ISP, but I had  
two problems:
	1.  The range pvc command works in 12.2.25S, but it has
	bugs, and when I opened a trouble ticket for the bugs,
	I found that the feature was not "supported" in this IOS
	version.
	2.  The S train doesn't include the ability to do ATM OAM
	pings, which is a damn useful feature that allows you to
	verify that your LEC has actually provisioned the circuit:

#ping
Protocol [ip]: atm
ATM Interface: atm2/0.4034
VPI value [0]: 4
VCI value [1]: 34
Loopback - End(0), Segment(1) [0]:
Repeat Count [5]:
Timeout [2]:
Type escape sequence to abort.
Sending 5, 53-byte end-to-end OAM echoes, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/11/12 ms

Hope this helps.  I have had no stability issues with 12.3T at all.

I also recommend checking out the book "Cisco ISP Essentials" from  
Cisco Press for lots of details on securing and managing a Cisco  
router in a border/ISP environment.  There are a lot of things on by  
default in IOS that shouldn't be in an ISP.

--
Roger J. Weeks
Systems & Network Administrator
Mendocino Community Network

On Dec 2, 2005, at 8:10 AM, cisco-nsp-request at puck.nether.net wrote:


> Date: Fri, 02 Dec 2005 10:09:42 -0600
> From: J Springer <js at jspringer.net>
> Subject: [c-nsp] 7206VXR for DSL Termination
> To: cisco-nsp at puck.nether.net
>
> We would like to convert our DSL from a Redback to a 7206VXR NPE400,
> 512M memory unit.
>
> Some questions/concerns that came up were:
>
> 1) number of VCs that this box could realistically handle
> 2) preference of which OC3 ATM card in the 7206
> 3) feedback from anyone that has an OC3 card in a 7206 connected to an
> AFC Telliant switch
> 4) preference of config (i.e. auto build pvcs vs static config)  
> when the
> DHCP requests will be relayed to a DHCP server for IP address
> assignment.  There will be no authentication.  Current Redback  
> config is
> bridged-1483 with each PVC restricted to its own bridged space  
> (secure ARP).
> 5) preferred IOS?  any additional licensing costs?
> 6) anything else we've missed?
>