The MPLS-OPS Archive

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

Mathew, would you go into a bit more detail on what you mean by
"off-line traffic engineering"? If you reference has me
stumped, I'll bet there are others out there with the same 
question.

Thanks much.

Roger Williams

At 06:25 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.
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.
3) You can support LSP constraints that are non-additive in nature -- since shortest path works by adding hop metrics.

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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