[c-nsp] IOS XR object tracking route reachability

[Aivars]

  I am trying to achieve conditional default route injection in VRF on
  ASR9k running 4.3.4. Similar configuration works on 7600 perfectly.
  I configured default static to null and attached track to it. When I
  started to configure tracks on 9k, I noticed that all of them are
  down. By the customer request I am tracking some classfull routes
  like 4.0.0.0/8 and 8.0.0.0/8. The configuration seemed to be pretty
  straight forward at first:

track 100
 type route reachability
  vrf x
  route ipv4 4.0.0.0/8
!
track 101
 type route reachability
  vrf x
  route ipv4 8.0.0.0/8

  As I mentioned, both are down, however I see the corresponding
  routes in the routing table:

  Routing entry for 4.0.0.0/8
    Known via "bgp xxxx", distance 200, metric 0
    Tag xxxx, type internal
    Installed Jun  2 08:03:36.518 for 07:17:30
    Routing Descriptor Blocks
      x.x.x.x, from x.x.x.x
        Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
        Route metric is 0
    No advertising protos.

Routing entry for 8.0.0.0/8
  Known via "bgp xxxx", distance 200, metric 0
  Tag xxxx, type internal
  Installed Jun  2 13:58:48.932 for 01:23:29
  Routing Descriptor Blocks
    x.x.x.x, from x.x.x.x
      Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
      Route metric is 0
  No advertising protos.

  Then I copied the configuration on one track to another 9k and got
  the same result - down. When playing around I changed the tracked
  prefix mask to /9 and got state UP. This is really confusing. I have
  both 8.0.0.0/8 and 8.0.0.0/9 in the routing table towards the same
  next hop and same metrics:

Routing entry for 8.0.0.0/8
  Known via "bgp xxxxx", distance 20, metric 0
  Tag xxxx, type external
  Installed Jun  2 02:03:09.123 for 19:49:09
  Routing Descriptor Blocks
   x.x.250.145, from x.x.250.145, BGP external
      Route metric is 0
      Label: None
      Tunnel ID: None
      Extended communities count: 0
  Route version is 0xab (171)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Route Priority: RIB_PRIORITY_RECURSIVE (8) SVD Type RIB_SVD_TYPE_LOCAL
 Download Priority 3, Download Version 1129312968
  No advertising protos. 
RP/0/RSP0/CPU0:BIP-P3#sh route vrf INET 8.0.0.0/9 detail 
Mon Jun  2 21:52:43.134 EEST

Routing entry for 8.0.0.0/9
  Known via "bgp xxxxx", distance 20, metric 0
  Tag 3356, type external
  Installed Jun  2 02:03:09.123 for 19:49:34
  Routing Descriptor Blocks
    x.x.250.145, from x.x.250.145, BGP external
      Route metric is 0
      Label: None
      Tunnel ID: None
      Extended communities count: 0
  Route version is 0xab (171)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Route Priority: RIB_PRIORITY_RECURSIVE (8) SVD Type RIB_SVD_TYPE_LOCAL
 Download Priority 3, Download Version 1129312956
  No advertising protos.

  Can someone please tell me where is the catch?