Thanks for an useful information, Richard.
Well, a DPC has a 1G ram inside and if each PFE has a complete copy of the
routing table (even the best route) and you are receiving a full feed of
internet and a thousands of your own routes, then all the 4 PFEs should occupy
the 1G RAM (I assume all 4 PFEs are using/sharing the DPC 1G ram to store
routing table) ...
not sure how to connect to a PFE individually, all I can do is 'start shell pfe
network fpc0' which connects you to a DPC and not the PFEs sitting somewhere on
the DPC :)
Regards,Andrew
> Date: Wed, 3 Nov 2010 12:20:06 -0500
> From: r...@e-gerbil.net
> To: go...@live.com
> CC: juniper-nsp@puck.nether.net
> Subject: Re: [j-nsp] routing updates between PFEs and Kernal
>
> On Wed, Nov 03, 2010 at 02:00:11PM +0500, Good One wrote:
> >
> > We started using MX-480 and I came to know that each DPC has four
> > PFEs. Now a question comes to mind that how the chemistry of routing
> > updates in between PFEs and RE(kernel) is being done. If kernel routes
> > are being exported to PFEs, does it means that each PFE contains a
> > full routing table? So if you have five DPCs than you have 20 PFEs and
> > you are exporting kernel routes to all 20 PFEs and each PFEs is having
> > a best route in the forwarding table.
>
> Yes each PFE has a complete copy of the routing table and makes the
> routing decision for ingress packets, this is how distributed forwarding
> works. I suspect what actually happens is the kernel sends it's routing
> table (krt) to the CPU on the DPC, which then programs the individual
> PFEs on the card (4 per DPC), but I don't work for Juniper or anything
> so I have no special knowledge about their implementation.
>
> There is also a fair amount of work that goes into locking and
> verification of the routes, to ensure that every PFE has a consistent
> view. Otherwise, you risk creating micro forwarding loops with every
> route update, or worse macro forwarding loops aka Cisco Customer
> Enragement Feature. :)
>
> --
> Richard A Steenbergen <r...@e-gerbil.net> http://www.e-gerbil.net/ras
> GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
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