This article discusses about RSVP unreserved bandwidth getting incorrectly set for ISIS LSPs and traffic engineering database.

The customer is setting reservable bandwidth as 94% or 95% and we can see that for some values, such as 95% we end up having greater reservable bandwidth in P0-P5 than the total reservable bandwidth. 

As per the customer, the Nokia support identified the problem as their implementation fails on the impossible situation where some RSVP priority bandwidth is great than total bandwidth.

This causes problems for some other vendor platforms such as IOX-XR/SROS, which will not be able to form 'least-fill' path through such interface.

As per the customer, they cannot see this problem on the Junos side, as the Junos renders bandwidth in Gbps, making priority and total appear to be same values. IOS-XR and SROS render in kbps, showing the problem.

[edit protocols rsvp interface ae0.0]
labroot@test-ptx10001# set subscription 94
==>
Global Pool BW Unreserved:
[0]: 93000000 kbits/sec [1]: 93000000 kbits/sec
[2]: 93000000 kbits/sec [3]: 93000000 kbits/sec
[4]: 93000000 kbits/sec [5]: 93000000 kbits/sec
[6]: 67874890 kbits/sec [7]: 67874898 kbits/sec
Reservable Global pool BW: 93000000 kbits/sec

[edit protocols rsvp interface ae0.0]
labroot@test-ptx10001# set subscription 95
==>
Global Pool BW Unreserved:
[0]: 95000003 kbits/sec [1]: 95000003 kbits/sec
[2]: 95000003 kbits/sec [3]: 95000003 kbits/sec
[4]: 95000003 kbits/sec [5]: 95000003 kbits/sec
[6]: 69874877 kbits/sec [7]: 69874877 kbits/sec
Reservable Global pool BW: 94999995 kbits/sec

Physical interface: ae0, Enabled, Physical link is Up
  Interface index: 1213, SNMP ifIndex: 516, Generation: 721554506879
  Description: BL: r15.labxtx03.us.bb be-2 - local wire
  Link-level type: Ethernet, MTU: 9188, Speed: 100Gbps, BPDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Enabled, Minimum links needed: 1, Minimum bandwidth needed: 1bps

The issue is not seen between two Juniper routers but can be seen when other vendor routers are involved.

In this case, the customer was unable to setup a 'least-fill' path when a non-Juniper router was in the path.

As per the engineering team, the Priority level bandwidth is rounded off but maximum reservable bandwidth is not rounded off in RSVP, which was causing this issue.