MPLS TE Admission control

[Mehdidz]

Hi Folks,

I'm pretty new to the MPLS TE topic, and I've a question for which I can't find an answer on my readings

 

let's  assume that we have the topology in the attached diagram

IS-IS is used as the IGP; with MP-BGP for VPN traffic, PE to CE is eBGP

Every link is a 10 Mbps link of which 6 Mbps are used by TE,

every node has a master tunnel which has   a default tunnel and an LLQ tunnel

the TE metric has been left by the default (equal to the IGP metric)

every single  node has tunnel to all other nodes (full mesh tunnels)

all tunnel interfaces have the config bellow 

interface Tunnel10

 description Tu RX (Master)

 bandwidth 10000

 ip unnumbered Loopback0

 tunnel mode mpls traffic-eng

 tunnel destination 169.254.1.2

 tunnel mpls traffic-eng autoroute announce

 tunnel mpls traffic-eng exp-bundle master

 tunnel mpls traffic-eng exp-bundle member Tunnel11

 tunnel mpls traffic-eng exp-bundle member Tunnel12

!

interface Tunnel11

 description Tu Rx (Default)

 bandwidth 6000

 ip unnumbered Loopback0

 load-interval 60

 tunnel mode mpls traffic-eng

 tunnel destination 169.254.1.2

 tunnel mpls traffic-eng autoroute announce

 tunnel mpls traffic-eng priority 7 7

 tunnel mpls traffic-eng bandwidth 4000

 tunnel mpls traffic-eng path-option 10 dynamic

 tunnel mpls traffic-eng record-route

 tunnel mpls traffic-eng fast-reroute

 tunnel mpls traffic-eng auto-bw frequency 300 adjustment-threshold 5 max-bw 4000 min-bw 1000

 tunnel mpls traffic-eng exp default

!

interface Tunnel12

 description Tu RX (LLQ)

 bandwidth 4000

 ip unnumbered Loopback0

 tunnel mode mpls traffic-eng

 tunnel destination 169.254.1.2

 tunnel mpls traffic-eng autoroute announce

 tunnel mpls traffic-eng priority 7 7

 tunnel mpls traffic-eng bandwidth sub-pool 2000

 tunnel mpls traffic-eng path-option 10 dynamic

 tunnel mpls traffic-eng record-route

 tunnel mpls traffic-eng fast-reroute

 tunnel mpls traffic-eng exp 5

My Questions are

1-     Having the default  MPLS TE metric equal to the IGP metric , and assuming that the path going to R9 through R8 is always the best path from an IGP point of view

the LSP being used to get from R1 to R9 is R1-R8-R9 and  all reservable bandwidth has been used (6 Mbps) , so we have 4 Mbps left on R8-R9

R2-R8-R9 is the best path (best Metric IGP/TE)

When RSVP signals the LSP to go to from R2 to R9 is the LSP going to be built using a less preferred path in terms of metric or will this result in and admission control failure?

2-     Is the sub-pool bandwidth dedicated from  the master tunnel interface or the Tunnel 12 ?

Many thanks in advance for your help

Kind regards

Mehdi

[mcusine · Accepted solution]

Hi Mehdi,

I am not sure if I undestood your question. But when you use MPLS TE with RSVP you can choice but path will follow to create the LSP, static or dynamic in you example you choice dynamic (follow the IGP metric path).

Now when the LSP try to make it the path followed goes trought the igp path, now RSPV will try to stablish the LSP with the bandwidth that you define.

Figure 1. RSVP Operation.

If the path have enought bandwidth the LSP will stablish and tunnel go up, but remember that is only admi reservation if you reserve 4MB and send 10MB of traffic the traffic will pass this is not a bandwidth guarantee.

I attach some interested links, one for concept and configuration :

http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-3/mpls/configuration/guide/b_mpls_cg43xasr9k/b_mpls_cg43asr9k_chapter_010.html#con_1130655

And another from the support community.

https://supportforums.cisco.com/discussion/9784116/mpls-te-tunnel-bandwidth-and-ip-rsvp-bandwidth

I don't know this help you but I tried.

Regards,

Mauricio

[Mehdidz]

Hi Mauricio,

When using dynamic path, thanks for your reply; let me try to rephrase my question pls:

If the best IGP path (R8-R9 on my diagram))has no more bandwidth left as per RSVP, when R2 wants to bring an LSP to R9 will this results in a creation of a new LSP (path over a sub-optimal path from an IGP point of view(like R2-R3-R4-R9) or will this result on an admission control failure and the new tunnel wont be up

Many thanks

Regards

Mehdi

[mcusine · Accepted solution]

Hi Mehdi,

I think yes, because when RSVP send the path message he send over all posible paths, in this case the best path not enought bandwidth and suboptimal path yes, the LSP will créate over the suboptimal path.

King regards,

[jngokgwe · Accepted solution]

Hi Mehdi,

MPLS TE using RSVP-TE builds a topology including the SPF paths and non-SPF ones. Based on additional constraints such bandwidth, priority, affinity, etc,,, MPLS TE relies on Constraint-SPF to setup LSPs filling the ingress needs.

In your scenario RSVP-TE will setup a new LSP on the paths meeting the ingress traffic flows requirements regardless of the cost of the links in the tree.  

I hope this helps