This was quite surprising and unpleasant surprise – IOS XR on ASR9k is not supporting GRE tunnels at the moment. It’s supporting IPSec and MPLS-TE but not GRE which is one of main and commonly used tunneling technique. You can define tunnel-ip interface but you can’t define source and destination handlers. GRE support is supposed to be in IOS XR 4.0 that might be released at the end of the year, but with Cisco you never know that.

This is what happens when you try to commit incomplete GRE tunnel configuration

RP/0/RSP0/CPU0:Aug 20 07:54:57.239 : tunl_gre_ma[426]: %FORWARDING-IP_TUNNEL-4-INIT : Tunnel-IP MA process failed to initialize platform tunnel IDs: 'Not supported' 
RP/0/RSP0/CPU0:Aug 20 07:54:57.913 : sysmgr[94]: tunl_gre_ma(1) (jid 426) (pid 430354) (fail_count 1) abnormally terminated, restart scheduled 
RP/0/RSP0/CPU0:Aug 20 07:54:57.913 : sysmgr[94]: %OS-SYSMGR-3-ERROR : tunl_gre_ma(1) (jid 426) exited, will be respawned with a delay (slow-restart)   
RP/0/RSP0/CPU0:Aug 20 07:54:57.915 : sysmgr[94]: %OS-SYSMGR-3-ERROR : tunl_gre_ma(426) (fail count 1) will be respawned in 10 seconds  
RP/0/RSP0/CPU0:Aug 20 07:54:57.915 : sysmgr[94]: %OS-SYSMGR-7-DEBUG : Feature:tunl_gre_ma tunl_gre_ma[426] (pid 430354) has not sent proc-ready within 90 seconds  
RP/0/RSP0/CPU0:Aug 20 07:54:58.021 : tunl_gre_ma[426]: %FORWARDING-IP_TUNNEL-4-INIT : Tunnel-IP MA process failed to initialize platform tunnel IDs: 'Not supported' 
RP/0/RSP0/CPU0:Aug 20 07:54:58.742 : sysmgr[94]: %OS-SYSMGR-3-ERROR : tunl_gre_ma(1) (jid 426) exited, will be respawned with a delay (slow-restart)   
RP/0/RSP0/CPU0:Aug 20 07:54:58.741 : sysmgr[94]: tunl_gre_ma(1) (jid 426) (pid 434450) (fail_count 1) abnormally terminated, restart scheduled 
RP/0/RSP0/CPU0:Aug 20 07:54:58.744 : sysmgr[94]: %OS-SYSMGR-3-ERROR : tunl_gre_ma(426) (fail count 1) will be respawned in 10 seconds  
RP/0/RSP0/CPU0:Aug 20 07:54:58.744 : sysmgr[94]: %OS-SYSMGR-7-DEBUG : Feature:tunl_gre_ma tunl_gre_ma[426] (pid 434450) has not sent proc-ready within 90 seconds  
RP/0/RSP0/CPU0:Aug 20 07:54:58.747 : sysdb_svr_local[408]: %SYSDB-SYSDB-7-STARTUP : Startup request for 'cfg/if/act/tunnel-ip666/v' from 'config' (jid 65808) failed for a process on a slow starting node 

% Failed to commit one or more configuration items during a pseudo-atomic operation. All changes made have been reverted. Please issue 'show configuration failed' from this session to view the errors