[j-nsp] FE Memory Upgrade

[Eric Van Tol]

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):

~~~~~~~~~~~~~~
o The command "show route summary" does not reflect the correct amount
of memory associated with each route. It just reflects the s/w
datastruct size (~72 bytes) does not include the allocation overhead of
24 bytes. 

So, each prefix in the RIB takes up approximately 96 bytes (~72 + 24).
This does not include the amount of DRAM taken up if you are doing
things on the router such as firewall filtering and uRPF.  In addition,
underlying functions such as the radix tree take up memory.
~~~~~~~~~~~~~~

In short, as another poster put it, you should be fine with the 768MB on
the RE and 16MB on the CFEB.  As a comparison, we have an M5 with 493K
routes in it that's only about 55% utilized with regard to memory.  CPU
is around 5%.

-eric

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Sabri Berisha
Sent: Tuesday, May 10, 2005 11:26 AM
To: info at beprojects.com
Cc: juniper-nsp at puck.nether.net
Subject: Re: [j-nsp] FE Memory Upgrade

On Tue, May 10, 2005 at 09:05:22AM -0500, info at beprojects.com wrote:
> We just purchased an M7i that we are going to use as a BGP router.  It

> came with 256M on the RE, which we are upgrading to 768M.  It has 128M

> on the CFEB and I was wondering if that needs to be upgraded as well.
I 
> know the RE memory is directly related to the number of routes you 
> receive, but what about the CFEB memory?  Is there a guideline as to
how 
> much memory you need for various applications?  Is it related to
routing 
> table size at all?  Or is it related to bandwidth?  Or?  Thanks.

AFAIK, the CFEB uses those 128M to store its OS, which does not
participate in the packet forwarding. For packet forwarding, there are
an additional 16MB of SSRAM available in which approx 900000 forwarding
entries fit.*

-- 
Sabri Berisha,
Juniper Certified - JNCIA #747	| Cisco Certified - CCNA
email: sabri at cluecentral.net	| cell: +31 6 19890416
http://www.cluecentral.net/	| http://www.virt-ix.net/

* assumption made based on the descripion of the FEB in my JNCIA books
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