The MPLS-OPS Archive

[Roger Clark Williams <rogerw@nordlink.com>]

It may be you are using the words differently. Traffic engineering, as a
design process, is done by people, perhaps using software to help make
the decisions. Those human routing decisions are then implemented on a
network using  the Layer 2/3 capabilities in place. "Traffic
engineering" as a phrase often used in MPLS conversation is the
process by which MPLS handles specified traffic and puts that traffic
over specified routes. The human decisions are implied but not stated.
When I say "an MPLS traffic engineered tunnel" the work of that
choice of routes is implied and we go on to talk about how RSVP works,
explicit vs. dynamic, failovers/fallbacks, etc.

Just a thought...

Roger Williams

At 12:22 PM 7/9/2002, you wrote:

Matthew, I don't understand what you're saying here. We may  be talking at cross purposes.

Traffic engineering (to me at least) is about controlling how traffic flows on your network. OSPF and IS-IS extensions allow those protocols to communicate resource reservations made on a router. MPLS is one means of instantiating paths through a network for selected traffic.

I thought off-line TE referred to looking at traffic flows and altering the way you setup TE in terms of how it directs traffic, how that TE is implemented is another question. Some other observations in-line

At 08:25 PM 7/8/2002, you wrote:

At 08:25 AM 7/5/2002 -0500, Christopher Lewis wrote:

Plain MPLS or MPLS VPN will work fine with distance vector protocols like EIGRP, but as mentioned a link state routing protocol is needed for MPLS traffic engineering, as each node needs the topology information those protocols provide and OSPF and IS-IS have the opaque LSA extensions necessary for traffic engineering.

To add to Chris' comments, note that this is for online "on the router" traffic engineering only. If you're doing off-line traffic engineering, any routing protocol that allows the control plane to operate will do.

Three benefits that offline TE offers vs. OSPF/IS-IS TE:
1) You can implement a routing algorithm that does a lot better than Dijkstra shortest path. For example, you can minimize overall network utilization and avoid bottlenecks.

MPLS TE using OSPF or IS-IS to communicate reserved resources does not rely on the Dijkstra algorthim to compute a path.

2) You can pre-calculate and install backup LSPs and ensure that there are no single points of failure, thereby dramatically improving LSP restoration time and guaranteeing resiliency.

As you can with MPLS TE and have fast re-route handle swap overs in less than 50 ms without operator intervention.

3) You can support LSP constraints that are non-additive in nature -- since shortest path works by adding hop metrics.

As you can with MPLS TE using OSPF or IS-IS extensions, things like affinity allow you to have the path include or exclude specified types of links in the path selection process for example.

Chris

Cheers,

Mathew

At 08:03 AM 7/4/2002, Roger Clark Williams wrote:

Zeevik has it right, but to add emphasis, OSPF and IS-IS are the only IGPs that support MPLS TE tunnels. Keep in mind, however, that Cisco IOS to my understanding supports only 32 routing processes per router, and OSPF must start a separate process each time it is used (unlike RIP and BGP). I am not sure right now whether IS-IS supports the use of address families within a single routing process (anyone?), but OSPF does not. Therefore, OSPF is good as an IGP in an MPLS cloud but has some limitations when used on a PE as both an IGP and a VPN routing protocol.

Roger Williams

At 02:07 PM 7/4/2002, you wrote:

Note that both IS-IS and OSPF have TE extensions to support Traffic Engineering. Thus means that the IGP also holds the amount of reserved and unreserved bandwidth on each link, affinity of links, etc. so protocols like RSVP-TE can find a path with the appropriate attributes of the tunnel.

-----Original Message-----

From: Gowda, Sidde [mailto:sidde.gowda@intel.com]

Sent: Thursday, July 04, 2002 07:43

To: 'amos'; mpls-ops@mplsrc.com

Subject: RE: [MPLS-OPS]: IGP

Hi

 

Not necessarily,

Any Link state protocols are OK for TE

But currently we have two ie OSPF and IS-IS.

So MPLS network uses them.

 

Siddu

-----Original Message-----

From: amos [mailto:slick@inter.net.il]

Sent: Friday, April 19, 2002 9:24 PM

To: mpls-ops@mplsrc.com

Subject: [MPLS-OPS]: IGP

Hi

 

from all the examples i saw, the interior gateway routing protocol for an mpls network is alwayes

ospf or is-is. is there any particular reason for that ?

i have a production network runing eigrp as the igp, we are now starting to employ mpls in the network,

and i would like to avoid migrating into a different igp at the moment.

 

10x

 

Amos

 

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