MPLS Traffic Engineering, Ospf Opaque lsa

[sivam siva]

Hi 

Can anyone explain what is the different meaning of TE-class 0-7 and how these values are used in Opaque LSA.

please see my below packet capture photo of Opaque LSA,

Interface bandwidth: 100 Mbps

RSVP reserved bandwidth: 1 Mbps

Bandwidth used by the tunnel: 500 kbps

Thanks 

Siva

[Giuseppe Larosa]

Hello Siva,

I think what we see is related to some properties of MPLS TE tunnels that are called setup priority and the priority of an already established tunnel.

In this priority scale the highest value is the worst.

The output indicates that the only configured TE tunnel has likely a setup priority and established priority in the range 5 to 7 as a result of this only the bandwidth for this lower priority pools are used and reduced to 500K of unused BW over a max of 1 Mbps.

You should be able to verify the current settings of the tunnel with

show mpls traffic-eng tunnel tunnelX

The default values for these priorities are not the most powerful ones.

The bandwidth parameter is only a nominal value. IF there is competition for TE resources the setup priority of the new tunnel is compared with the "established " priority of existing tunnels and it can pre-empt / take over causing reroute of a tunnel already in place.

The setup priority value can be equal or worse= higher of the "established" value to avoid instability.

Your tunnel might have a setup priority of 7 the worst and an establised priority of 5.

As a result of this the 500K value is subtracted only from priority 5 to 7.

Hope to help

Giuseppe

[sivam siva]

Hi @Giuseppe Larosa 

Thank you for the reply

I can understand the use of setup and hold priority, but couldn't understand how these priority values impact the unreserved bandwidth field of OSPF Opaque lsa, 

can you explain the below output which I have taken in router R3?

path taken by tunnel 6= R6-R4-R3-R2-R1

path taken by tunnel 7= R6-R5-R3-R2-R1

Thanks

Siva

[Giuseppe Larosa · Accepted solution]

Hello Siva,

in the output the values inside the TLV are expressed in bytes/s instead of bps, as a result of this everything is divided by 8.

Priority classes 0 to 3 are left untouched to 2500000 bytes / s = 20 Mbps .

The tunnel 7 having setup priority and hold priority 4 reduced the unrserved bandwidth for pool Pri 4 and all the lower values by a 12500 bytes/ s = 100 Kbps.

Tunnel 6 does the same but from traffic class priority 5 to 7 and with a stated bandwdith of 500 kbps = 62500 bytes /s of reduction.

The end result is that traffic classes 5 to 7 have an unused bandwidth of 2500000 -12500 -62500 = 2425000 bytes /sec.

Why a tunnel with priority 4 impacts on traffic classes 4 to 7: because a new tunnel with setup priority 4 to 7 cannot take its place over the link. This is the reason why the unused bandwidth is reduced in multiple classes the Constrained SPF must take in account that the resource is not available for those levels of priorities.

Your lab test clearly show this one tunnels impacts on traffic classes from 4 to 7 and the other one from 5 to 7 and this also shows that the hierarchy is the lowest priority is the best.

For a new tunnel with setup priority 3 and bandwidth 20 Mbps is configured it will be able to setup using R3 : gi3/0 and will cause the tunnel 6 and tunnel 7 to be rerouted.

Hope to help

Giuseppe

[sivam siva]

That's awesome explanation @Giuseppe Larosa