Segment-routing TE bug? experienced on XR and XE

[Alan_4]

Whats up Cisco forum users,

So i am experiencing something weird, basically when i mention the explicit-path in the segmented routed Tunnel (with the command 'path-option 10 explicit name path1 segment-routing' , for example) the Tunnel does not work but show mpls traffic-eng tunnels would show the tunnel and path as up. I have experienced this with IOS-XR and IOS-XE (virtual, both of them). But whenever i remove the statement segment-routing from the command, the tunnel just works fine (so that would be 'path-option 10 explicit name path1')

Can anyone explain whether this is normal, docs show the segment-routing statement.

i am guessing it is just a virtual appliance bug? Is there any difference between using this statement or not?

startup cfg of an XR attached, note; it does not work neither with mentioning the nodes in the explicit path with their SID label-id or their loopback address

[Harold Ritter]

Hi Alan,

This should work. Try configuring the isis interfaces as point-to-point. Can you also provide the output from "show mpls traffic tunnels" and "show isis segment-routing label table".

Regards,

[Alan_4]

On XE it did suprisingly work after i mentioned the path with their labels, so in other words the segment-routing statement means that the explicit path should contain only SR labels (i guess).

But on XR it is just not cutting it, i also fixed the whole network as p2p isis links but still no success, i am pretty confident it is some sort of bug, just like other minor things i noticed such as traffic steering in mpls-te tunnels. (thats for another talk but basically when you do autoroute announce on a tunnel then the steering works, but if you were to do a static route for the tunnel end, a /32 pointing to the te-tunnel, then it just does not work, weirdly enough on IOS XE it is the vice-versa, because there if you mention autoroute announce it does not work, but a static route to steer the traffic over the TE tunnel does work)

I have attached a picture of show mpls traffic tunnels, output looks just right, so i doubt there really is a configuration mistake. after all ios xe with the same config does let me route the traffic over tunnels where the explicit path has the mentioned 'segment-routing' keyword.

but thanks anyway

[Harold Ritter · Accepted solution]

Hi Alan,

> On XE it did suprisingly work after i mentioned the path with their labels, so in other words the segment-routing statement means that

> the explicit path should contain only SR labels (i guess).

It should actually work regardless you specify an explicit path with labels or IP addresses.

> But on XR it is just not cutting it

The tunnel shows as UP/UP, right? Can you let us know how you have determine that the data plane doesn't work?

>  (thats for another talk but basically when you do autoroute announce on a tunnel then the steering works, but if you were to do a static > route for the tunnel end, a /32 pointing to the te-tunnel, then it just does not work

You should bear in mind that the entire SRTE semantic is changing on XR. The tunnel interface is considered legacy and will eventually disappear. XR now uses SR policies (under segment-routing traffic-engineering stanza), which allows you to perform automated steering (among other things).

Regards,

[Alan_4]

Hello Harold,

Yes, the tunnel is showing up as up/up. Because it is a virtual environment it is very easy for me to start a Wireshark in the middle of the path, and to no surprise it doesn't show any data being send along the path when i send a ping/traceroute from a client node located in a l3vpn site. (its a simple setup of is-is , sr , bgp,  l3vpn)

also, thanks for the headsup, i did not know that the focus is being shifted towards SR policies instead of TE tunnels

By the way when a client sends a ping over these non-functioning tunnels then he gets ICMP unreachables.

[Harold Ritter]

Hi Allen,

Can you provide the output of a "show cef 103.1.1.1 det". 

It would also be worth to try to convert the interface based configuration into the new policy based configuration.

Regards,

[Alan_4]

Hello Harold,

Apologies for the late reply, i guess your reply came in my spam mail folder hence i never got to see your message.

I however had great success with the policy based structure of configuring SR TE so once again thanks for the info.

The show cef output i sadly wont be able to provide since i don't have this lab setup anymore but who knows ill set this up again somewhere in the near future (for researching purposes)..