Autoroute Announce Absolute Metric

Load mpls.te.autoroute.announce.metric.xr.init.cfg

#IOS-XE
config replace flash:mpls.te.base.config.with.isis.cfg

#IOS-XR
configure
load bootflash:mpls.te.base.config.with.isis.cfg
commit replace

Setup a dynamic TE tunnel from XR11 to CSR9. Configure autoroute annouce so that R8, R1, R4, and R9 are only reachable via the tunnel interface. But make sure that all destinations have the same exact IGP cost in the RIB.

Answer

The autoroute annouce absolute metric knob sets the static metric for the tunnel, and also uses this same metric for any destinations beyond the tunnel. Destinations beyond the tunnel do not increment in IGP cost.

#XRv11
int tunnel-te0
 autoroute announce metric absolute 19

Note that this metric change happens after SPF has fully run. So for example, if we set this to 21, then the tunnel will not be used to get to R1, R4, and R8, even though those routes have a total IGP cost of 30. Additionally, the tunnel will not be used to R9 since the tunnel cost (21) is higher than the IGP cost to R9 (20).

#XRv11
int tunnel-te0
 autoroute announce metric absolute 21

Interestingly, setting this to 20 also removes any ECMP paths. This is because the IGP paths have a higher cost than the TE paths once the metric absolute command adjusts the TE paths from 30 down to 20.

#XRv11
int tunnel-te0
 autoroute announce metric absolute 20

Compare this to simply using autoroute announce with the default metric of 20:

#XRv11
int tunnel-te0
 autoroute announce
  no metric absolute 20