Well, to give a little more info on what the article below said,
If they are Point-to-Point, you have to create a sub-interface for each PVC,
so you are limited to the number of IDBs you can have in a router. I think
the numbers in that article might be a bit low, but it might be correct for
most models. Our Cisco rep recently told us that a 7200VXR routers were
limited to 3,000 IDBs, although I think the VXR chassis is one of those geek
things it was talking about :)
If they are Multipoint PVCs, the numbers below look pretty good to me, but a
bit conservative for a max value. We have a bunch of Cisco 4700s with 16M
DRAM, and each of them has 4 T1s on them with 200 PVCs per T1, for a total
of about 800 per router.
Hope that helps.
Mike
>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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