PBTS on ASR 9k

[gogie]

I'm trying to implement Policy Based Tunnel Selection on ASR 9k. Official documentation is completely wrong about it, stating we should use "policy-class" command. Instead, I was told by TAC a while ago that we should be using "forward-class", which should be assigned by policy-map type pbr on inbound interface. I couldn't find any documentation about it.

TAC also mentioned that 

"Any traffic that does NOT match the configured policy definition, will be
associated with this default-class, and only TEs associated with
default-class will be used for forwarding. Similarly, if the traffic is
classified to forward-class X, but there is no TE associated with this
class (X), then, the traffic will use the
 default-class TEs. (Note that if there is no TE in the default-class,
then the packet will be DROPPED in this case)."

What I'm seeing on 9k with 5.1.3 is that in absence of "default tunnel" any traffic without explicitly configured tunnel for that class follows tunnel with smallest forwarding class, and in absence of any tunnel, just normal IGP path. Even in MPLS L3 VPN environment, when pbr is applied to interface in VRF and BGP next-hop of VPN prefix is routed over TE tunnel.

I wonder if I'm not looking at things correctly, or DROP behavior was changed in 5.1.3.

Any additional info on PBTS feature will be appreciated.

[xthuijs]

Aik, that's not good, apologies for this. Can you do me a favor please and submit feedback on that CCO documentation article and refer to our discussion here please?

I'll work with our documentation folks to rectify this and make it a bit better.

In the meantime I found one doc Ihad on the troubleshooting part that I posted here:

https://supportforums.cisco.com/document/12454066/asr9000xr-policy-based-tunnel-selection-troubleshooting-and-verification-guide

I didnt format it that nicely, yet, but will clean it up but wanted to get it out to you.

cheers

xander

[gogie]

Hello Xander,

Thanks for help. As always, Your posts are best info source on IOS XR.

As for official PBTS docs, right now i'm having SR 634087583 and they mentioned some 
CSCur97889 opened to correct the documentation. 
5.x.x documentation on PBTS is useless.
4.1.3 does have some information, but is wrong in configuration part,
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_0100.html#task_1313266
still mentions "policy-class". There is section on "forward-class" nearby, but still not very clear.

For thechnical issues around PBTS, I'll ask under Your "PBTS(Policy based tunnel selection) Feature Troubleshooting Guide" post.

Regards
George

[xthuijs]

hey george, thank you, nice to hear!!

I checked the ddts and spoke with the doc manager, it is in the works to be addressed and beefed up!

We can either use this discussion to hash out the issues you are seeing or we can do it under the doc post. This discussion here may be better, so that everyone sees the updates, which are not easy to track when they are posted under the doc...

But I am fine either way :)

cheers!

xander

[gogie]

My main concern is about what happens when traffic is assigned some non-default class by PBR and there is NO TUNNEL AT ALL (no class-specific, no default) for that destination.

4.3.1 doc says "All non-TE interfaces through the destination route was learned will be pushed down by routing protocol to the forwarding plane with forwarding class set to default-class." 

I understand it as "no matter what  forward-class is assigned by PBR, if there is no TE tunnel to given destination, traffic will follow normal IGP path". Is it correct?

In my scenario, I get traffic in VRF interface and do inbound QoS marking MPLS EXP imposition based on incoming DSCP. If I want PBTS on the same interface to classify based on newly imposed MPLS label stack EXP, I should use "service-policy apply-order qos pbr", right?

Any plans for supporting PBTS on BVI interfaces?