[c-nsp] DWDM optics on 6500s

[Nick Hilliard]

On 05/10/2009 15:35, Jeff Bacon wrote:
> Admittedly, for the cost, I can buy an arista 1U for wave passthru and
> just tap multiple 1Gs over to the 6500.

Aristas use SFP+.  Good luck running colours over them. :-)

Actually, Optoway in Taiwan produce CWDM SFP+ transceivers.  I don't know 
anyone using them, but given the power constraints imposed by the SFP+ form 
factor, I wouldn't expect long reach or anything.

> Why "particularly with 6704 blades"? Is there something particularly
> wrong with them?

Depends on what you do with them.  They are a first generation blade, and 
are 6yo technology at this stage and, well, things have moved on since 
2003.  XENPAK is moribund as a transceiver type which means that any money 
you invest into buying transceivers will probably be written off when you 
retire the blade.

If you're concerned about storm control (which personally, I am), the 6704 
can only limit to 0.33% of port capacity, which means that if you get a 
broadcast / multicast storm on a 6704 port, it will bang out 33 megs of 
data before storm control even notices.  Most hosts will happily ignore the 
multicast traffic, but the broadcast traffic could cause serious trouble.

If you need to push wire-speed 10G on a 6704, there are conflicting reports 
as to whether this works well.  Some people say yes; others no - there's 
lots of discussion about this in the c-nsp archives.  It can help to use a 
DFC if you're banging out a lot of traffic, but that's extra €€€ on top of 
a product which already has a high cost per port.

The 6708 is lots better than the 6704 if you operate it in non- 
oversubscribe mode, apart from anything else, it has a built-in DFC, which 
means that you don't need to retrofit this for high traffic environments.

As I said, it depends on what you want to do.  If you're running just a 
couple of gigs and don't care about the broadcast traffic problem or, say, 
are using them for L3 traffic instead of L2, then they are great. 
Similarly, the C65k+sup720 platform makes a really nice high density, 
feature rich 1G platform.  But if you're planning to run lots of very high 
bandwidth stuff, it might be better to use a different platform.

Nick