LISP ETR periodically sends UDP based map registration message to map server. This results in control traffic and scalability problems. TCP based reliable map registration or LISP reliable map registration mechanism is developed as an enhancement and replacement to the UDP based map registration mechanism.

The LISP reliable map registration mechanism as shown in the figure is described below:

• ETR sends UDP based map registration message to map server.

• Map server processes map registration and sends map-notify to ETR. This message serves as acknowledgment.

• ETR initiates a TCP session with map-server using three-way handshake.

  Note	When TCP based map registration is not supported by map server then ETR uses UDP based map registration to establish a session with the map server.

• Once the TCP session is established, map-server sends a registration refresh message to the ETR.

• ETR sends map registrations to the map server through the TCP connection.

• Map server acknowledges for the map registrations.

Note	There are no configuration commands for this feature. This feature is turned on automatically.

Perform this task to verify the LISP Reliable Registration feature which is enabled automatically in the LISP network. In this example, a LISP site uses a single edge router that functions as both ITR and ETR (known as an xTR). Routing Locators (RLOCs) are in IPv4. EID prefixes are in both IPv4 and IPv6. The LISP site registers to two map server/map resolver (MSMR) devices in the network core. The topology used in verifying LISP Reliable Registration is as shown in the figure below.

The components as shown in the topology are described below:

In the following output, a ‘#’ sign in the ‘Up’ column indicates reliable map registration session.

Device# show lisp site

LISP Site Registration Information
* = Some locators are down or unreachable
# = Some registrations are sourced by reliable transport
 
Site Name     Last     				Up     	  Who Last         Inst    		 EID Prefix
              Register     					     Registered       ID      
A							      never    			 no       			  --                 			  0.0.0.0/0
              01:59:44 				yes#    	 203.0.113.11             		 10.10.10.0/24
              01:59:44 				yes#   		 203.0.113.11            			 10.20.20.0/24
              01:59:44				 yes#    		203.0.113.11             		 172.16.0.0/24
              01:59:44 				yes#    		203.0.113.11             		 2001:DB8::/32
B				         never    				no     					  --                      0.0.0.0/0
              never     			no     					  --                      10.0.0.0/8
              01:59:43 				yes#      198.51.100.21           			 10.30.30.0/24
              01:59:43 				yes#      198.51.100.21           		  10.40.40.0/24
              never     			no      	 				--                     	21.0.0.0/8
              01:59:43 				yes#      198.51.100.21           		  21.21.21.0/24
              01:59:43 				yes#      198.51.100.21            		 2001:DB8::/48

In the following output, no ‘#’ sign in the ‘Up’ column indicates that the Old MSMR does not support reliable map registration.

Device# show lisp site

LISP Site Registration Information
* = Some locators are down or unreachable
 

Site Name     Last     				Up   					Who Last         Inst     	 EID Prefix
              Register    								   Registered       ID      
A							      never    			 no  									 --                      0.0.0.0/0
              00:00:00 				yes 						203.0.113.11                172.16.0.0/24
              00:00:55 				yes 						198.51.100.21               21.21.21.0/24
              00:00:03 				yes 						203.0.113.11                2001:DB8::/32
B							      never     			no  									 --                      10.0.0.0/8
              00:00:00 				yes 						203.0.113.11                10.10.10.0/24
              00:00:00 				yes 						203.0.113.11                10.20.20.0/24
              00:00:55 				yes 						198.51.100.21               10.30.30.0/24
              00:00:55 				yes 						198.51.100.21               10.40.40.0/24
              00:00:52 				yes 						198.51.100.21               2001:DB8::/48

The following output is from xTR1 that uses 2 map servers. Reliable map-registration session is established with 209.165.201.31 (New MSMR), but not with 209.165.201.41 (Old MSMR).

Device# show lisp session
 
Sessions for VRF default, total: 2, established: 1
Peer                           State     Up/Down       In/Out   Users
209.165.201.31                 Up         05:05:40       6/3     2
209.165.201.41                 Down       never          0/0     1

The following output is from New MSMR. It has established reliable map-registration sessions with two ETRs.

Device# show lisp session
 
Sessions for VRF default, total: 2, established: 2
Peer                           State     Up/Down       In/Out   Users
203.0.113.11                   Up         05:19:53       3/6     1
198.51.100.21                  Up         05:18:28       2/5     1