[j-nsp] Very basic question about MPLS and RSVP's place in the design

Scott Granados scott at granados-llc.net
Wed Oct 26 18:38:22 EDT 2016

Hi Alex, thanks for these pointers.  I’m not sure I grasp all this yet but I think this will get me started.  As someone else mentioned I think I’ll start reading one of the fundamentals books and get my head around proper design.  Maybe this sort of thing isn’t something I should be doing or concerned with.

Thank you again

On Oct 26, 2016, at 2:06 AM, Alexander Arseniev <arseniev at btinternet.com<mailto:arseniev at btinternet.com>> wrote:


Some answers:

A. bandwidth reservation is per outgoing interface that RSVP LSP takes and it is not truly global meaning that of course ingress LSR knows all the link bandwiths in given IGP domain but if there is "no bandwidth" signaled by upstream nodes, then ingress LSR router takes it at face value and Your LSP setup will fail. In fact, there could be BW attained by "repacking of existing LSPs to outgoing interfaces" in a different way but JUNOS does not do repacking. To achieve a truly global view of available and reserved BW, You need a centralised controller called Northstar but I digress.

B. To map different VRFs to different LSPs You'd need forwarding-table policy with "install-lsp" knob


Only equal-cost LSPs are considered in this policy. If Your two parallel LSP have different cost (by default they shouldn't as the default LSP cost is the minimum IGP cost to destination loopback) then You'd need to play with "no-install-to" and "install" knobs coupled with VRF nexthop rewriting to map different VRFs to different LSPs




On 26/10/2016 01:34, Scott Granados wrote:

Hi, this is a very basic question at least I think it is, apologies for being so green in advance.

I’m trying to wrap my head around MPLS and have built a small lab.  I understand how provider routers label switch packets and how provider edges use VRF instances and their distinguishers and targets to address each other.  Per the Juniper examples I have LDP and RSVP enabled on all the transit interfaces along with MPLS and obviously the correct interface families (MPLS) attached to the same transit interfaces.

I then per the doc built a label switched path something like.

set protocol MPLS label-switched-path r1-r4 to
;destination loopback of R4 which is acting as a PE
I have an equal return to 1 built as well
I also have a bandwidth reservation defined
set protocol MPLS label-switched-path R1-R4 bandwidth 10M
and a reverse reservation as well

As I understand you build these relationships between the loopbacks.  My question is how does this relate to the VPN VRF entries on the provider edges?  Is this a global value that reserves 10 megabits between R1 and R4?  What if you want to reserve 10 megabits and 5 megabits between R1-R4-VRF1 <> R4-r1-vrf1  and r1-r4-vrf2 <> r4-r1-vrf2 where you have two matching sets of VRFs on the same PE pairs.  Is this possible or do I have the function of RSVP confused?

Again sorry for the n00by question I’m just trying to figure out how all the pieces fit together.  If anyone has any reference pointers that might be  a good start that explains this I would be interested as well.  The Juniper documentation is quite good but I can’t figure this out via searching so far.  Any pointers would be most appreciated.

Thank you


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