""Howard C. Berkowitz"" <[EMAIL PROTECTED]> wrote in message
news:p05001905b6d4554abd7f@[63.216.127.100]...
> Depending on the design of the core, the routers at the edge of the
> core will use full routes to set up MPLS LSPs from one side of the
> core to the other, but routers internal to the core may not need it
> if they are under LDP or RSVP-TE control from the edge routers.
>
> If you think of the core as interconnecting the POP/access and server
> sites inside an ISP or an enterprise, there's a good deal of interest
> in subsecond reconvergence times. This probably is achievable with
> link state IGPs, using millisecond or microsecond hellos (or relying
> on hardware failure detection on optical links), and more advanced
> algorithms than the 40-year-old Dijkstra.
>
> In the short to moderate term, there is no foreseeable way to get
> convergence times this fast with exterior routing. Actually,
> superfast convergence in the global Internet may be a Really Bad Idea
> with respect to Internet stability.
I don't think I've seen POP/access or server sites that are implementing
subsecond reconvergence (especially on the collocation side) with even
IGPs at this point. Combining this with some of the other concepts you
brought up is very key. To add another one into the mix, try to solve the
problem of stateful failover using "n to many" clustering/high-availability
for servers in these environments. Bringing this to the network layers
becomes difficult when considering multiple paths and convergence,
be it long-haul, metro, or even across logical local areas (VLANs)
at the lower network layers, or external or internal routing at the higher
network layers (IGP, MPLS-TE, Content routing, Content switching, etc).
> This is a huge discussion right here. I agree that a very high
> density of logical interfaces is the requirement for an ISP "edge"
> rather than "core" router. The aggregation to these interface may
> very well be in what variously is called the access or collection
> tier.
>
> While there's no industry consensus on terminology for the hierarchy
> associated with ISPs, Cisco has been getting away from
> core/distribution/access in some of its carrier-oriented
> presentation. The newer usages seem to be:
<snipped redefinition of network hierarchy>
> I will be co-organizing a session this June at the Internet Society
> meeting in Stockholm, along with Lyman Chapin of Verizon/GTE/BBN
> (chair) and Sue Hares of NextHop. One of our goals is to present
> multivendor views of what constitutes the edge. There's certainly no
> consensus, and I haven't begun to discuss content routing here.
Howard, thank you for defining some new terminology. I always feel
that certain words can help me understand something better ;>
In terms of understanding this big picture, I have been coming to terms
with new designs for edge networks and trying to fit all these concepts
together. Content networking is the big one that seems to break a lot
of the mold of networking (as I know it, at least) that we've come to
rely on over the years. So I deeply understand the need for consensus.
Sounds like Stockholm will be ground-shaking ;>
> Absolute agreement that we need a term. Some people call these core
> routers "because they are part of the Internet core," but it's really
> stretching it to say that the Internet has a distinct core.
>
> Can you get along with the idea that an ISP core router has lots of
> bandwidth, perhaps lots of MPLS paths, perhaps a big _forwarding_
> table (as distinct from routing table), but not much filtering or
> policy controls? Limited traffic conditioning? Also, all its
> interfaces tend to be the same general speed.
Core networks (as you describe them here) are definitely changing.
I am having a hard time with the idea of Carrier's Carrier networks,
and some of the other challenging concepts with core networking.
I always thought of the Core as where IBGP lives, not "passed over",
as in transport. It sounds like your concept of a core here is an IGP
carrying infrastructure addresses and maybe "a bunch of LSRs".
If this were ATM overlay and not MPLS, would it still be called the
same thing? What if it's Optical? What if it's MP(Lambda)S?
So, yes, "Internet core" as in carrying Internet (or ISP customer)
prefixes. But, no, not "Internet core" as in exchanging prefixes with
other AS's (although I'm sure IBGP mesh, route-reflection, and
confederations complicate the idea even further -- but at least these
terms are currently well understood and defined).
Hrmn... how about "BGP Core" and "Core Transmission"? These
are words taken from Cisco. BGP Core could define IBGP
carrying Internet/customer prefixes across/into/throughout the
ISP backbone. Core Transmission could define the MPLS-TE
and/or MPLS VPN architecture (LSRs and P-routers) and the
underlying transport (could be IP+ATM, could be Optical, etc).
> In contrast, an ISP edge router has lots of logical interfaces,
> extensive filtering, policy, and traffic shaping. It has the most
> extensive routing (I am including the "border" function here). It
> may be asymmetrical with respect to interfaces (e.g., 10/100/1000
> Ethernet toward the customer, OC-48 or better toward the core)
Extensive routing and extensive filtering. Sounds like the classic
Cisco distribution layer, which I guess is moving up in the world ;>
So why the term "edge" here instead of "distribution"?
There are so many different devices that provide "edge" services
that work on different layers and have totally different functionality,
this becomes very confusing. A carrier is going to have a totally
different perspective than a Hosting ISP. Some "edge" devices
offer some interface capabilities and not others. Some "edge"
devices offer certain [QoS|VPN/Security] policies and not others.
-dre
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