We actually are using a 3640 with a T1 controller. We currently have about
30 sub-interfaces and everything seems to be working fine. I am trying to
find the limitations of my routers. Even if we get multiple T1 controllers,
if there is a limit of 60 DLCIs (or 80, or whatever) per router, that is
something I need to know about for my spending projections.
The problem I am trying to solve is "To add another 100 to 200 remote
offices to our FR WAN, what additional hardware will need to be purchased?"
It makes sense to me to learn the limitations of the routers (memory, CPU,
interface speed), and see how things can be done as cheaply as possible.
>From there, more money can be spent to solve issues or limit risk as
necessary. There is no problem that more money cannot be thrown at, but for
the money to be effective in this case I have to know the inherent
limitations of the router.
Why would the 2500 die with 60 sub-int into one interface? What would cause
it to die? Is the limitation the shared memory space? How can I get better
planning numbers?
Thanks,
Dave
-----Original Message-----
From: Andy Harding [mailto:[EMAIL PROTECTED]]
Sent: Thursday, June 08, 2000 7:02 PM
To: David Smith; Study group (E-mail)
Subject: Re: Frame Relay limitations question
Dave,
To quote HCB yet again "WPAYTTS?" (What problem are you trying to solve?)
This should be considered in context - don't ever think about running 60
sub-int into a 2500, it would just die before your eyes. If you work for
that large a company that you need 1000s of DLCIs to converge on one
location, do you really want them to all to terminate on one port, on one
router, on one single point of failure? If you are serious about
resilience, which I assume you are (I hope at least), then spread stuff
around a little. 2500s are Access routers - ie one per remote site with
maybe a couple of PVCs at most. At a pinch I would terminate maybe half a
dozen PVCs on one at a concentrator site, but I would much prefer a couple
of 2600s, or a 3600, or bigger kit as the situation dictates.
bear in mind what you are paying for the circuits - WAN bandwidth ain't
cheap (if it is for you and you're in the UK then mail me back now!). It's
worth balancing the cost of your circuits, router hardware, and the cost of
downtime to arrive at a suitable compromise.
HTH
Andy
----- Original Message -----
From: David Smith <[EMAIL PROTECTED]>
To: Study group (E-mail) <[EMAIL PROTECTED]>
Sent: Thursday, June 08, 2000 3:48 PM
Subject: Frame Relay limitations question
> Hi all,
>
> I am doing some projections for growth in our companies FR cloud. I was
> checking the limitations of routers when I came across this article. The
> link is below.
>
> http://www.cisco.com/warp/public/125/26.html
>
> The following is directly from the article. The last part is what I have
a
> question about. Does anybody know where the limitations per router
platform
> come from? The article seems to be missing some information about why the
> 2500 can only support 60 DLCIs, the 4000 can support 120, etc.
>
> Thanks in advance,
> Dave
>
> DLCI Limitations
> Subinterfaces count toward the practical upper limit of 230 Interface
> Descriptor Blocks (IDBs). In other words, Cisco IOS currently doesn't
> support more then 230 interfaces on the router (real or virtual) unless
you
> have an ISP Geeks Image which has 1024 IDBs. How many DLCIs can one
> configure per physical interface? How many DLCIs can one configure in a
> specific router? These two questions are frequently asked.
Disappointingly,
> the answer is, "it depends."
> DLCI address space: Approximately 1000 DLCIs can be configured on a single
> physical link, given a 10-bit address. Because certain DLCIs are reserved
> (vendor-implementation-dependent), the maximum is about 1000. The range
for
> "cisco" LMI is 16-1007. The stated range for ANSI/ITU is 16-992. These are
> the DLCIs carrying user-data.
> LMI status update: The LMI protocol requires that all permanent virtual
> circuit (PVC) status reports fit into a single packet and generally limits
> the number of DLCIs to less than 800, depending on the maximum
transmission
> unit (MTU) size.
> MTU= 4000 bytes Max DLCIs app= (MTU bytes - 20 bytes)/ (5 bytes/DLCI)
> (4000-20)/5 = 796
> Default MTU on serial interfaces is 1500 bytes, yielding a maximum of 296
> DLCIs per interface. Please note that these numbers vary slightly,
depending
> on the LMI type. The maximum DLCIs per router (not interface) platform
> guideline, based on extrapolation from empirical data established on a
Cisco
> 7000 router platform, are listed below:
> * Cisco 2500: 1 X T1/E1 link @ 60 DLCIs per interface = 60 total
> * Cisco 4000: 1 X T1/E1 link @ 120 DLCIs per interface = 120 total
> * Cisco 4500: 3 X T1/E1 links @ 120 DLCIs per interface = 360 total
> * Cisco 4700: 4 X T1/E1 links @ 120 DLCIs per interface = 480 total
> * Cisco 7000: 4 X T1/E1/T3/E3 links @ 120 DLCIs per interface = 480
> total
> * Cisco 7200: 5 X T1/E1/T3/E3 links @ 120 DLCIs per interface = 600
> total
> * Cisco 7500: 6 X T1/E1/T3/E3 links @ 120 DLCIs per interface = 720
> total
> Note: These numbers are guidelines only, and assume that all traffic is
> fast-switched.
>
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