[c-nsp] 1841 suitable for BGP?

[Gert Doering]

Hi,

On Fri, Sep 01, 2006 at 06:28:45PM -0300, Everton da Silva Marques wrote:
> > What you describe is true for process switching, but if
> > you *are* doing process switching, you have much worse
> > problems than the BGP scanner.
> 
> I used to assume that the 1841 router was deprived of
> any ASIC-assisted forwarding mechanism (think TCAM-like),
> and thus packet switching would be fully performed by
> software in the main CPU; 

This is correct for *all* Cisco devices up to a 7200.

The 7304 has PXF, the 7600 has TCAM based forwarding.

> the performance distinction
> between process switching and CEF switching would lie
> entirely in the software path triggered by the incoming
> packet. That is, only the low priority of processes
> like BGP scanner would prevent those processes from
> routinely disrupting the CEF switching performance.

The whole point of CEF is that it's happening in the incoming-packet-
interrupt.

So there is nothing a process can do to interrupt CEF forwarding.

> I suppose you are saying that either:
> 1. 1841 does have some kind of specialized hardware for
>    packet forwarding, presumably programmed from CEF FIB

No.

> 2. the CEF path somehow executes at a higher priority
>    than processes like BGP and process-switching
>    (huh, is process-switching an actual process?);
>    hence CEF-switching performance would be less
>    affected by ordinary processes (compared to
>    process-swiching)
> ?

Yes.  CEF happens when the incoming interface signals an interrupt
"hey, a packet has arrived!".

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de