ODR (On-Demand Routing)

On-Demand Routing (ODR) is an enhancement to Cisco Discovery Protocol (CDP), a protocol used to discover other Cisco devices on either broadcast or non-broadcast media. With the help of CDP, it is possible to find the device type, the IP address, the Cisco IOS® version running on the neighbor Cisco device, the capabilities of the neighbor device, and so on. In Cisco IOS software release 11.2, ODR was added to CDP to advertise the connected IP prefix of a stub router via CDP. This feature takes an extra five bytes for each network or subnet, four bytes for the IP address, and one byte to advertise the subnet mask along with the IP. ODR is able to carry Variable Length Subnet Mask (VLSM) information. 

[Ref.:http://www.cisco.com/en/US/tech/tk365/tk810/tsd_technology_support_sub-protocol_home.html]

network setup:

 

R1-R2-R3 [Spokes] Configuration:

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
no aaa new-model
memory-size iomem 5
ip cef
!
no ip domain lookup
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/0
 ip address 155.1.0.1 255.255.255.0
 encapsulation frame-relay
 clock rate 2000000
 cdp enable
 frame-relay map ip 155.1.0.4 101 broadcast
 no frame-relay inverse-arp
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 no ip address
 shutdown
 clock rate 2000000
!
ip forward-protocol nd
!no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
!
end

R5 Configuration:

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R5
!
boot-start-marker
boot-end-marker
!
no aaa new-model
memory-size iomem 5
ip cef
!
no ip domain lookup
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!

interface Loopback0
 ip address 5.5.5.5 255.255.255.255
!
interface FastEthernet0/0
 ip address 155.1.45.5 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
ip forward-protocol nd
!
no ip http server
no ip http secure-server
!        
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
end

R4 [Hub] Configuration: 
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R4
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
ip cef
!
no ip domain lookup
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!
interface Loopback0
 ip address 4.4.4.4 255.255.255.255
!
interface FastEthernet0/0
 ip address 155.1.45.4 255.255.255.0
 duplex auto
 speed auto
!
interface Serial0/0
 no ip address
 encapsulation frame-relay
 clock rate 2000000
!
interface Serial0/0.1 multipoint
 ip address 155.1.0.4 255.255.255.0
 snmp trap link-status
 cdp enable
 frame-relay map ip 155.1.0.1 401
 frame-relay map ip 155.1.0.2 402
 frame-relay map ip 155.1.0.3 403
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 no ip address
 shutdown
 clock rate 2000000
!
router odr
!
ip forward-protocol nd
!
no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
end

In order for the ODR to work we have to configure on each serial interface the command: cdp enable


on the Hub router enable ODR routing with the command: router odr

the routing table on the spoke routers:

R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is 155.1.0.4 to network 0.0.0.0

     2.0.0.0/32 is subnetted, 1 subnets
C       2.2.2.2 is directly connected, Loopback0
     155.1.0.0/24 is subnetted, 1 subnets
C       155.1.0.0 is directly connected, Serial0/0
o*   0.0.0.0/0 [160/1] via 155.1.0.4, 00:00:01, Serial0/0


All spokes, which are stub networks, pointing deault route to R4 while R4 has routes to all other routers:

R4# show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     1.0.0.0/32 is subnetted, 1 subnets
o       1.1.1.1 [160/1] via 155.1.0.1, 00:00:10, Serial0/0.1
     2.0.0.0/32 is subnetted, 1 subnets
o       2.2.2.2 [160/1] via 155.1.0.2, 00:00:19, Serial0/0.1
     155.1.0.0/24 is subnetted, 2 subnets
C       155.1.0.0 is directly connected, Serial0/0.1
C       155.1.45.0 is directly connected, FastEthernet0/0
     3.0.0.0/32 is subnetted, 1 subnets
o       3.3.3.3 [160/1] via 155.1.0.3, 00:00:10, Serial0/0.1
     4.0.0.0/32 is subnetted, 1 subnets
C       4.4.4.4 is directly connected, Loopback0
     5.0.0.0/32 is subnetted, 1 subnets
o       5.5.5.5 [160/1] via 155.1.45.5, 00:00:01, FastEthernet0/0

take note that this can only be done when all routers are Cisco and running CDP protocol.