[c-nsp] Sharing router uplinks?

[Mark Tinka]

On Wednesday, August 01, 2012 05:46:30 PM Saku Ytti wrote:

> It is doable but not optimal. It is questionable if any
> benefits can be extracted in well designed network this
> way.

I've had discussions with other operators in the past, who 
have been used to have a direct interconnect between routers 
in the PoP, and optionally, links to an Ethernet switch to 
aggregate downstream devices.

I've tended to re-use the switched capacity and ignore the 
point-to-point link between the routers, at all bandwidth 
levels. Been doing that for the last several years, and no 
major drama - especially if you're not fully utilizing the 
ports on a point-to-point link.

Certain topologies will require traffic mapping between 
routers more consistently, but those would be few and far 
between at the scale points affecting this decision, 
depending on the operation, e.g., MPLS-TE, IGP-based load 
sharing from upstream/downstream of the core network, e.t.c.

> - You can possibly save port counts,...

Which is not an unreasonable goal, particularly if ports 
cost additional money, space or power that one might not 
have.

> but you lose
> hardware liveliness detection, as you have switch
> between core devices. Which means high convergence time
> (lower quality) and possibly increased complexity (BFD).

I've been running such topologies for several years, and IS-
IS + BFD have not inconvenienced me once, whether in drills 
or real failure scenarios.

Cheers,

Mark.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part.
URL: <https://puck.nether.net/pipermail/cisco-nsp/attachments/20121001/8570b03c/attachment.sig>