[j-nsp] FE Memory Upgrade

[Richard A Steenbergen]

On Tue, May 10, 2005 at 12:04:07PM -0400, Eric Van Tol wrote:
> I have no M7i experience, but I can tell you that an M20 with an SSB-E
> and 64MB DRAM/8MB SRAM could only handle about 500K routes in the Rib
> before it started to issue allocation errors.  768MB on the RE and 16MB
> SRAM on the CFEB will do you fine, as long as you're not going to use it
> to create 15 logical-routers, all with a copy of a full BGP table ;-)
> 
> I received a good explanation from Juniper about how the memory
> allocation in the SSB (or CFEB in your case) is handled (paraphrased
> from JTAC):

That would be your SRAM that ran out, not the SSB DRAM. The DRAM is used 
to hold the next-hop table, which can run out if you have a large amount 
of arp entries on an ethernet interface for example.

As it was described to me, the nhdb L2 descriptor size is hard coded as a 
percentage of your DRAM. On a 64MB DRAM model, this comes out to just over 
50k:


SFM2(xxx.xxx vty)# show nhdb zones
Chip  Start   Size   Rsvd   Used/Hi Water/Total  Size  Name
----  -----  -----  -----  --------------------  ----  ----
   0  20000  01000  00000               0/0/512     8  Multicast RTP
   0  21000  02400  00000              0/0/9216     1  Multicast Lists
   0  23400  04400  00006         176/180/17408     1  Next-Hop Entries
   0  27800  18800  0004b         856/885/50176     2  L2 Descriptors
                                  ^^^^^^^^^^^^^

If you have 50k arp entries on your system, it can exhaust the max L2 
descriptors. The Juniper answer is to buy a new switch board which has 
128MB of DRAM on it. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)