Subject: grow: what is most complex

From: Loa Andersson <[email-masked]>
Date: Mon, 22 Mar 2004 22:31:17 +0100

All,

I've have what might be a naive question and it might not be derived
from actual operational experience. But I've not seen it explicitly
addressed.

If we are looking at what drives complexity most in the operations
of a network, is that:

- adding more more and more information to be carried by existing
   protocols

or

- adding more and more protocols for singular purposes?

/Loa

-- 

Loa Andersson

mobile +46 739 81 21 64

_________________________________________________________________
web user interface: http://darkwing.uoregon.edu/~llynch/grow.html
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From: Jeffrey Haas <[email-masked]>
Date: Mon, 22 Mar 2004 16:56:31 -0500

My somewhat out of date operational opinion:

> - adding more and more protocols for singular purposes?

Getting whatever you need to Solve Your Problem.

How you do that depends on what tools are available and how much
pull you have over the tool makers.

There's also the problem of Leveraging Existing Clue.

If you know BGP and it looks like it would almost fit in there, you
want it in BGP.  (Never mind the minute you mumble the words
"inter-domain".)

-- 
Jeff Haas 
NextHop Technologies

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From: Pedro Roque Marques <[email-masked]>
Date: Mon, 22 Mar 2004 14:11:40 -0800 (PST)

Loa Andersson writes:

> All, I've have what might be a naive question and it might not be
> derived from actual operational experience. But I've not seen it
> explicitly addressed.

> - adding more and more protocols for singular purposes?

Loa,
Assuming that we are talking about problems w/ similar caracteristics
(i.e. that your algorithm to disseminate information is similar) your
complexity increases significantly each time you add a new
implementation of the same algorithm (both software and in terms of
operations).

Algorithms are ment to be independent of the purpose the data is used
for. Talking about the usage of the data is meaningless.

  Pedro.

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From: Jeffrey Haas <[email-masked]>
Date: Mon, 22 Mar 2004 20:13:21 -0500

As was pointed to me off list, I failed to note the word "operational".
That should teach me to respond to mails quickly while short on sleep. :-)

> - adding more more and more information to be carried by existing

Adding stuff onto an existing protocol potentially allows clue on
that protocol to scale into new features.

> - adding more and more protocols for singular purposes?

This creates clear separation and may simplify applications quite
a bit.  However, if the thing you're adding the protocol for already
has similar functionality elsewhere, then the layering approach may
work better protocol wise.

What are the consequences of each of these?  One example would be
2547 VPNs.

Configuring a plain IP forwarding autonomous system is reasonably
complex.  You need to setup an IGP, BGP in the appropriate places,
and relevant policy in order to just get yourself properly announced.

Add simple MPLS on this.  In at least one case (LDP), configuring
it is reasonably simple.  In another case (RSVP), you increase
the complexity by having another layer of full-mesh added.
If you actually have a need for MPLS style traffic engineering,
then this complexity is additionally messy.

Then add on 2547 VPNs which may require BGP speakers whose only
purpose is VPN access on the network.  The interactions as this
overlaps, or doesn't with your current BGP network adds complexity.
You'll also need to manage the cases where you want to leak routes
between the two.

In each of these cases, we leverage things that lie underneath.
The things done by each layer could be done as a completely different
protocol, but since common forwarding infrastructure is shared, you
don't want them to get out of synch.  This also seems to argue for
layering.

IMO, it's also unlikely that you could reduce the complexity in configuration
for many of these things.  Thus, regardless of the protocol, its
configuration complexity that governs many of the problems in an
operator's network.

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From: Pedro Roque Marques <[email-masked]>
Date: Mon, 22 Mar 2004 17:44:08 -0800 (PST)

> This creates clear separation and may simplify applications quite a
> bit.

Separation of what ? In terms of network operations what is the
separation that does matter ?

Note that different applications of the same protocol are implemented
using completly distinct tables... e.g. isis multi-topology or
multiple BGP RIBs.

How does it help operationally to use different code paths ? Does it
offer any meaninful separation to the operator.

A useful comparison is to take the example of ospfv3 vs isis IPv6
extensions. I believe there is a general consesus that ospfv3 was
substantially harder to deploy... does it give operators any added
value in terms of separation ? and if so is it worth the cost ?

  Pedro.