[c-nsp] Sup720 vs RSP720 - Difference?

[Phil Mayers]

Rick Ernst wrote:
> Thanks to everyone for the feedback so far.
> 
> For my situation, the two biggest items that stand out are:
>  - 4GB vs 1GB RAM
>  - 7600 chassis only, not 6500 (planning on a 7600 chassis, though)
> 
> I'm a bit surprised that you are seeing ~60%  memory used by BGP. My
> border routers (4 routers, 1 full feed each) and core (route-reflectors)
> are both only showing about 25% memory used, total.

I guess the poster is taking more than one full feed (see below) which 
consumes more ram.

> 
> Since the Sup720 (spec-wise, at least) capacity is roughly 2 orders of
> magnitude higher than I'm currently pushing through the core, it looks

By "spec-wise" I assume you mean forwarding rates? The 6500/7600 
platforms are indeed very fast.

> like it should serve for several years.  The RSP720 becomes an upgrade
> option if 1GB is no longer big enough for full tables (plus IPv6
> roll-out?).
> 
> On the subject of memory and DFCs... do the DFCs also support 4GB for the
> FIB, or is this an apples vs oranges comparison?

It doesn't work that way. FIB is held in TCAM, not RAM.

PFC/DFCs some in two forms - XL and non-XL.

XL can hold ~1M FIB entries, with some commands to divide this up 
between v4, v6 and so on. Notably, this is more than sufficient to hold 
a full table.

non-XL can hold 256k entries, which is not sufficient for a full table.

So, for full-table applications, ensure you get a sup with XL PFC and 
that *all* your linecards have XL DFCs.

Also be aware, as discussed recently - holding >1 full feed on a 
6500/7600 does not consume more FIB entries - it just uses sup RAM, 
since only one FIB entry is installed per prefix.

I see in your original post you mentioned netflow - you will probably 
want to have a look through the archives for the (many, long) threads 
where people document their problems with netflow on this platform. 
Specifically, like the FIB, the DFCs have limited TCAM slots for netflow 
entries (256k/1M on non-XL/XL) and you can over-run this TCAM if you 
have a lot of traffic.

If the netflow is important to you, and you're likely to have >1M flows 
at any given time, you might want to consider alternatives.