[j-nsp] Optimizing the FIB on MX

[Adam Vitkovsky]

> Alexander Marhold [mailto:alexander.marhold at gmx.at]
> Sent: Thursday, February 18, 2016 6:50 PM
>
> Hi folks
>
> To make the discussion clearer and comming back to the Juniper MX 104
> implementation
>
> Here is a picture of 2 PEs on P  and 2 peers (ISP1 and IX1) let´s assume we
> want to prefer routes from IX1 over ISP1
> MX1 is EBGP (lpref 100) to  ISP1 and IBGP to MX2 and MX3
> MX2 is EBGP (lpref 110) to IX1 and IBGP to MX1 and MX3
>
>   ISP1                   IX1
>     | locpref         ^ locpref
>     |   100              |   110
>    MX1--------->-MX2
>     |                               |
>     |                               |
>     +------MX3--->--+
>
>
> In my opinion if you need also  the MX3 then  for this MX3 you need "PIC-
> CORE" to quickly switch between both paths
>
Yes that's right, "protect core" under routing-options of the Internet VRF.

However then I can ask what if MX2 fails or is severed from the core completely,
though with that I'd be opening a whole different and very interesting realm of convergence options.
First you'd need to tune your IGP so it propagates the unreachability of MX2's loopback towards MX3 as fast as possible.
Then I could argue that MX3 is in a different AS and it knows about MX2's loopback via BGP-LU -so you'd need to tune BGP-LU infrastructure(can't shave of much delay).
Then I could argue I want sub 50ms convergence in the above case and well then, then you'd have to rely on P routers to perform the local repair and swing from MX2 to MX1 If MX2 goes down.
And that brings me to Segment Routing and protecting a node segment upon the failure of its advertising node


> On MX1 you need "best-external" to advertise the external routes whereas
> the best is the internal route pointing to MX2
>
> On MX1 and MX2 you need "PIC-EDGE" to quickly switch when IX1 goes
> down
>
Well technically you need PIC-EDGE only on MX2 so it can do the local repair for traffic destined to IX1 and re-label it so that it gets to MX1.

> Do we all agree on that picture and the named mechanisms ( put in "") ?
>
>
> So now what versions of Junos is needed and what additional "unnecessary"
> methods like MPLS or LDP is now needed ?
>
Well I'm afraid you'd need to run MPLS L3VPNs for all this.


adam


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
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