[c-nsp] forced path MPLS tunnel question

[Mark Tinka]

On Wednesday, January 18, 2012 12:01:27 AM Gert Doering 
wrote:
 
> For the "verbatim!" paths, having the point-to-point
> next-hops listed (and having "mpls traffic-eng tunnels"
> on the interface) seems to be sufficient - it's now
> working for a somewhat smaller-than-planned test rig,
> but it *is* working :-)  (and I have learned something).

Gert, just so you know, when you're doing explicit routing 
in MPLS-TE and your IGP (OSPF or IS-IS, if you do choose to 
run them in the future) domains are multi-area (OSPF) or 
multi-level (IS-IS), then you need to deploy Inter-Area 
MPLS-TE.

Inter-Area MPLS-TE calls for a so-called Expanded Loose Hops 
configuration, where nodes in an LSP path are defined 
"loosely" as opposed to "strictly" ("loosely" means that 
routers along the path will need to determine the best path 
through which to signal the LSP, while "strictly" means the 
LSP is signaled specifically on the defined path, whether it 
is the best or not).

Now, the reason I'm writing this is to warn you of the 
differences in deploying Inter-Area MPLS-TE between IOS/IOS 
XE and IOS XR.

In IOS and IOS XE, defining the physical interface IP 
addresses in your ERO (Explicit Route Object), just like 
you're doing now, will work. But in IOS XR, the only 
supported addressing in the ERO are the Router ID's, i.e., 
the Loopback interfaces.

If you try to define the ERO in IOS XR with the physical 
interface address, the LSP won't be signaled.

PS: in case you're wondering, strict ERO's are not supported
    for Inter-Area MPLS-TE.

PS: for us, some of the MPLS services we run do not like
    Inter-Area MPLS-TE, so we maintain a flat Level-2 IS-IS
    domain (or in the OSFP case, this would be a flat Area 0
    across the entire backbone).


Hope this helps.

Cheers,

Mark.
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