[c-nsp] Rant: ASR1000 MPLS (not) load-balancing

adamv0025 at netconsultings.com adamv0025 at netconsultings.com
Fri Jan 3 06:59:03 EST 2020

> From: Saku Ytti <saku at ytti.fi>
> Sent: Friday, January 3, 2020 8:24 AM
> On Thu, 2 Jan 2020 at 18:14, Robert Raszuk <robert at raszuk.net> wrote:
> >> There is no reason for IP to simpler or more complex in control-plane
> >> compared to MPLS.
> >
> >
> > Disagree.
> >
> > WIth flat MPLS transport labels must be present to reach all of your
> > 100s or 1000s of LSP endpoints in another IGP area or your other
> > global AS. Think VPN Option-C
> >
> > With IP transport all I need is a *single* IP summary route to my other area
> or AS.
> >
> > I hope control plane difference is clear now.
> It  is not, you are looking particular implementations, which have no implicit
> correlation to the actual bytes imposed, either could do either. Only thing
> which matters is what are the lookup keys and how many are there. What
> algorithmic solution do I need in HW to find rewrite information for those
> lookup keys.
Hey Robert, Happy new year!
On a theoretical fundamental level I have to agree with Saku here, 
Think SDN controller implementation of CP for instance, the control-plane complexity of Intra-AS vs Inter-AS LSP programming is exactly the same in this example. 

However on practical level, 
You're right in the complexity argument in a sense that we have to work with/support technology we currently have installed -which isn't pure SDN controlled Inter-AS setup, but more like ISIS + LDP/RSVP at the intra-AS layer and BGP-LU at the Inter-AS layer. And all the headaches (and elaborate hacks) around scaling in absence of summarization especially in setups with MPLS all the way to the access layer (e.g. cell-tower eNode B in RAN).


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