It can be challenging to obtain optimal bin packing without significant network disruption and/or bandwidth over-booking when RSVP-TE LSPs are reserving bandwidth in a network in a PCE controlled network. A complex and involved process of make-before-break(MBB) LSP creation and LSP preemption is needed to optimize an existing network. Using Northstar's Zero-Bandwidth mode enables a PCE to route LSPs without considering the reservation style of the network or that a LSP set-up maybe rejected due to BW overbooking when a MBB operation is performed. This allows the PCE to optimize resource utilization more effectively and more aggressively thereby achieving greater network efficiency.
But we still need to go deeper down into final details of certain end-to-end connectivity use cases. And based on these use cases, I can finally compare some aspects from both the 6PE model and this architecture. These aspects are covered in this second post.
I am pretty sure many readers will find some other advantages or caveats and I would much appreciate some other points of view on this topic. Please feel yourself invited to drop here your opinion and comments, take the attached Junosphere topology, and modify it and break it if possible!
Traffic-Engineering shortcuts is a feature that implements shortcut next hop attachments beyond an RSVP-TE LSP (Label Switched Path) egress point. It allows using RSVP-TE LSPs as best next hop to interconnect an ingress LSR (Label Switching Router) performing shortcut computation and destinations beyond the egress LSRs themselves.
Junos OS 9.3 major release introduced a per-family enhancement on top of the Traffic-Engineering shortcuts feature to apply such calculations for IPv6 destinations, among others, when the IGP is IS-IS. In this case, computed IPv6 prefixes that turn reachable through RSVP-TE LSPs are injected into inet6.3 and become eligible as IPv6 next hops.
At first, you may conceive the feature suitability to interconnect dual-stack routers with a single and common LSP. But actually, this is a more powerful tool! Because shortcuts are applicable to destinations further downstream than the LSP egress point, this feature does not only provide connectivity to IPv6-enabled systems but complete IPv6-enabled islands. It effectively allows a replacement option for the full 6PE model using native inet6 unicast BGP families for IPv6 prefix distribution, instead of inet6 labeled unicast.
With this post and its follow-up, I explore this feature including hands-on with a Junosphere topology as a feasible replacement for the 6PE model and provide a practical comparison of both implementations. You may notice it is the same physical topology previously used in my MPLS ipv6-tunneling for 6PE and 6VPE models post, so please feel free to play around as well with both topologies and share your opinion and comments about both architectures!