[j-nsp] Upgrade from M10i?

[Richard A Steenbergen]

On Wed, Feb 04, 2009 at 08:17:12AM -0800, ken lindahl wrote:
> p.s.: it's worth noting that adding "tunnel PIC capability" to an MX, in 
> order to have it act as an RP, uses a full slot in the chassis.

Not exactly... At worst you disable a full "pic" (1/4th of the DPC card) 
to create a tunnel, at best you don't have to disable anything at all 
(for a 1G tunnel).

If you look at the architecture of the MX, basically what Juniper did
was to use a large number of distributed 10G packet forwarding engines
(PFEs) functioning in parallel rather than a smaller number of faster
(but more expensive) PFEs, to create a platform that is optimized for
doing 1/10GE. Each DPC is actually 4 individual PFEs, each with its own
I-chip, controlling either one 10GE port or a group of 10x1GE ports. 
These appear as "PICs" within JUNOS (even though they aren't physically
remoevable), but unlike traditional pics which contain only interface
components (not routing components), each "PIC" functions as its own
PFE.

When you go to create a "tunnel pic" interface, what you're actually
doing is stealing some PFE capacity for use on your tunnel service. 
Since the MX doesn't use pluggable cards, there is no physical tunnel 
"PIC", it's just a softward controlled loopback. Remember that the 
tunnel "PIC" on other platforms doesn't actually do anything other than 
create a physical loopback and identify itself to the chassis (there is 
about $10 worth of electronics on one :P), what it's actually doing is 
taking some PFE capacity by blocking off those PIC slots.

On the MX you have the option of creating either a 1G or 10G tunnel, 
though currently you don't have a choice in the matter because you are 
restricted to using 1G or 10G based on the type of card ("PIC" PFE 
actually) inserted. If the PFE is controlling a 10GE port, you can only 
create a 10G tunnel port, which disables the physical 10GE port. If the 
PFE is controlling 10x1GE, you can only create a 1G tunnel port. Now the 
interesting thing is that each PFE is actually capable of doing 11Gbps, 
so when you create a 1G tunnel port on a 10x1GE PFE it doesn't actually 
disable any of the existing ports it just creates a "pic 10" interface. 
The rumor mill has it that the 10GE PICs are capable of doing this too, 
and at some point in the future the software will support creating a 1G 
tunnel on a 10GE PFE without disabling the physical interface.

The same rules apply to the newer mixed cards (2x10GE + 20xSFP) and 
limited cards (2x10GE only), each "PIC" is still either a 1x10GE or 
10x1GE, all they're doing is mixing and matching the types onto 
different cards to satisfy configuration requirements without needing to 
make the interfaces swappable.

-- 
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)