Note: You must perform Lab 0 for loading the initial configurations before starting this lab.
● Configure OSPF in area 12345 over the DMVPN cloud, between R1 - R5.
✓ Use a OSPF network type of point-to-multipoint.
✓ Advertise Loopback0 prefixes in area 12345.
● Configure OSPF in area 0 between R5 and R8.
Configurations
R1 - R5:
!
enable configure terminal
!
interface Tunnel0 ip ospf 1 area 12345 ip ospf network point-to-multipoint
!
interface Loopback0 ip ospf 1 area 12345
!
end
!
write
!
R5:
!
enable configure terminal
!
interface GigabitEthernet0/2 ip ospf 1 area 0
!
end
!
write
!
R8:
!
enable configure terminal
!
interface GigabitEthernet0/0 ip ospf 1 area 0
!
end
!
write
!
Verifications
OSPF network type point-to-multipoint is specifically designed to solve reachability problems in partially meshed NBMA network designs. Like network type point-to-point, it sends hellos as multicasts and does not support the DR/BDR election. Unlike point-to-point, however, multiple adjacencies on a single interface aresupported. When adjacency is established, the show ip ospf neighbor output indicates that there is no DR or BDR for the segment with the null output in the Statefield:
R5#show ip ospf neighbor tunnel 0
Neighbor ID Pri State Dead Time Address Interface
170.1.2.2 0 FULL/ - 00:01:55 177.1.0.2 Tunnel0
170.1.3.3 0 FULL/ - 00:01:40 177.1.0.3 Tunnel0
170.1.1.1 0 FULL/ - 00:01:32 177.1.0.1 Tunnel0
170.1.4.4 0 FULL/ - 00:01:58 177.1.0.4 Tunnel0
Verify the OSPF network type used:
R5#show ip ospf interface tunnel 0
Tunnel0 is up, line protocol is up
Internet Address 177.1.0.5/24, Area 12345, Attached via Interface Enable
Process ID 1, Router ID 177.1.5.5, Network Type POINT_TO_MULTIPOINT, Cost: 1000
Topology-MTID Cost Disabled Shutdown Topology Name
0 1000 no no Base
Enabled by interface config, including secondary ip addresses
Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Gi0/2 1 0 177.1.58.5/24 1 BDR 1/1
Lo0 1 12345 170.1.5.5/32 1 LOOP 0/0
Tu0 1 12345 177.1.0.5/24 1000 P2MP 4/4
The spokes of the network only form adjacency with R5, and not each other, because multicast OSPF packets are not sent between spokes:
R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
177.1.5.5 0 FULL/ - 00:01:32 177.1.0.5 Tunnel0
R2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
177.1.5.5 0 FULL/ - 00:01:46 177.1.0.5 Tunnel0
R3#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
177.1.5.5 0 FULL/ - 00:01:31 177.1.0.5 Tunnel0
R4#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
177.1.5.5 0 FULL/ - 00:01:46 177.1.0.5 Tunnel0
The output from the show ip ospf database in area 12345 also reinforces the fact that there is no DR or BDR for the segment. Recall from the DR/BDR election section that the Network LSA (LSA 2) is used to describe the DR and its attached neighbors. Because there are no DRs for any transit links in area 12345, the Net Link States (Area 12345) section does not appear in the below output for area 12345:
R5#show ip ospf database
OSPF Router with ID (177.1.5.5) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
177.1.5.5 177.1.5.5 148 0x80000004 0x000FBF 1
177.1.8.8 177.1.8.8 141 0x80000003 0x00D1EF 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
177.1.58.8 177.1.8.8 156 0x80000001 0x00BF43
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
170.1.1.1 177.1.5.5 209 0x80000001 0x007372
170.1.2.2 177.1.5.5 209 0x80000001 0x005E85
170.1.3.3 177.1.5.5 209 0x80000001 0x004998
170.1.4.4 177.1.5.5 209 0x80000001 0x0034AB
170.1.5.5 177.1.5.5 209 0x80000001 0x00EADE
177.1.0.1 177.1.5.5 209 0x80000001 0x0019C7
177.1.0.2 177.1.5.5 209 0x80000001 0x000FD0
177.1.0.3 177.1.5.5 282 0x80000001 0x0005D9
177.1.0.4 177.1.5.5 282 0x80000001 0x00FAE2
177.1.0.5 177.1.5.5 282 0x80000001 0x00BC0C
Router Link States (Area 12345)
Link ID ADV Router Age Seq# Checksum Link count
170.1.1.1 170.1.1.1 386 0x80000002 0x0059A0 3
170.1.2.2 170.1.2.2 386 0x80000002 0x00866B 3
170.1.3.3 170.1.3.3 386 0x80000002 0x00B336 3
170.1.4.4 170.1.4.4 386 0x80000002 0x00E001 3
177.1.5.5 177.1.5.5 282 0x80000002 0x00BFEF 6
Summary Net Link States (Area 12345)
Link ID ADV Router Age Seq# Checksum
177.1.58.0 177.1.5.5 282 0x80000001 0x00781A
When LSA replication is complete, the next change that should be evident is how the routing table is processed on the DMVPN segment between the neighbors. For example, take the following view of the network from R1’s perspective:
R1#show ip route ospf
Codes: L - local, 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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
170.1.0.0/32 is subnetted, 5 subnets
O 170.1.2.2 [110/2001] via 177.1.0.5, 00:07:33, Tunnel0
O 170.1.3.3 [110/2001] via 177.1.0.5, 00:07:33, Tunnel0
O 170.1.4.4 [110/2001] via 177.1.0.5, 00:07:33, Tunnel0
O 170.1.5.5 [110/1001] via 177.1.0.5, 00:07:43, Tunnel0
177.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
O 177.1.0.2/32 [110/2000] via 177.1.0.5, 00:07:33, Tunnel0
O 177.1.0.3/32 [110/2000] via 177.1.0.5, 00:07:33, Tunnel0
O 177.1.0.4/32 [110/2000] via 177.1.0.5, 00:07:33, Tunnel0
O 177.1.0.5/32 [110/1000] via 177.1.0.5, 00:07:43, Tunnel0
O IA 177.1.58.0/24 [110/1001] via 177.1.0.5, 00:06:00, Tunnel0
For all routes that are learned from the hub of the DMVPN network, the next-hop value has been updated to the interface IP address of the hub. With the broadcast
network type, the DR does not update the next-hop. The result of this is that when route recursion is performed for traffic that must be routed between the spokes,
NHRP resolution needs to be performed for the hub, not for the spoke (hub NHRP entry is statically configured on all spokes):
R1#show ip route 170.1.2.2
Routing entry for 170.1.2.2/32
Known via "ospf 1", distance 110, metric 2001, type intra area
Last update from 177.1.0.5 on Tunnel0, 00:10:42 ago
Routing Descriptor Blocks:
* 177.1.0.5, from 170.1.2.2, 00:10:42 ago, via Tunnel0
Route metric is 2001, traffic share count is 1
R1#show ip route 177.1.0.5
R1#show ip route 177.1.0.5
Routing entry for 177.1.0.5/32
Known via "ospf 1", distance 110, metric 1000, type intra area
Last update from 177.1.0.5 on Tunnel0, 00:11:14 ago
Routing Descriptor Blocks:
* 177.1.0.5, from 177.1.5.5, 00:11:14 ago, via Tunnel0
Route metric is 1000, traffic share count is 1
R1#show ip route 177.1.0.5
Routing entry for 177.1.0.5/32
Known via "ospf 1", distance 110, metric 1000, type intra area
Last update from 177.1.0.5 on Tunnel0, 00:11:14 ago
Routing Descriptor Blocks:
* 177.1.0.5, from 177.1.5.5, 00:11:14 ago, via Tunnel0
< 0 > IP midchain out of Tunnel0, addr 177.1.0.5 10756500
IP adj out of GigabitEthernet0/0, addr 169.254.100.5 0FE08B30
Subblocks:
None
R1#ping 170.1.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 170.1.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 5/6/7 ms
From views outside of the connected segment, the point-to-multipoint network is only seen as a collection of endpoints, not a transit segment itself. For example,
review the following output on R8, which is in area 0:
R8#show ip route 177.1.0.0 255.255.255.0
% Subnet not in table
R8#show ip route ospf | i 177.1.0.
177.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
O IA 177.1.0.1/32 [110/1001] via 177.1.58.5, 00:12:19, GigabitEthernet0/0
O IA 177.1.0.2/32 [110/1001] via 177.1.58.5, 00:12:19, GigabitEthernet0/0
O IA 177.1.0.3/32 [110/1001] via 177.1.58.5, 00:12:19, GigabitEthernet0/0
O IA 177.1.0.4/32 [110/1001] via 177.1.58.5, 00:12:19, GigabitEthernet0/0
O IA 177.1.0.5/32 [110/1] via 177.1.58.5, 00:12:19, GigabitEthernet0/0
R8 does not have an exact match for the prefix 177.1.0.0/24, which is the actual subnet assignment of the DMVPN Network. Instead, it knows that there are five endpoints on the network: 177.1.0.1, 177.1.0.2, 177.1.0.3, 177.1.0.4, and 177.1.0.5.This is the normal and desirable behavior for OSPF network type point-to-multipoint, according to the RFC standard. This can also be viewed at the database level, where each router in the DMVPN cloud, in its Type1 LSA, it advertises its own IP address with a /32 mask and additionally it advertises its OSPF neighbors on the segment which is required for a complete OSPF database view:
R1#show ip ospf database router self-originate
OSPF Router with ID (170.1.1.1) (Process ID 1)
Router Link States (Area 12345)
LS age: 961
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 170.1.1.1
Advertising Router: 170.1.1.1
LS Seq Number: 80000002
Checksum: 0x59A0
Length: 60
Number of Links: 3
Link connected to: a Stub Network
(Link ID) Network/subnet number: 170.1.1.1
(Link Data) Network Mask: 255.255.255.255
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 177.1.5.5
(Link Data) Router Interface address: 177.1.0.1
Number of MTID metrics: 0
TOS 0 Metrics: 1000
Link connected to: a Stub Network
(Link ID) Network/subnet number: 177.1.0.1
(Link Data) Network Mask: 255.255.255.255
Number of MTID metrics: 0
TOS 0 Metrics: 0
R5#show ip ospf database router self-originate
OSPF Router with ID (177.1.5.5) (Process ID 1)
Router Link States (Area 0)
LS age: 856
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 177.1.5.5
Advertising Router: 177.1.5.5
LS Seq Number: 80000004
Checksum: 0xFBF
Length: 36
Area Border Router
Number of Links: 1
Link connected to: a Transit Network
(Link ID) Designated Router address: 177.1.58.8
(Link Data) Router Interface address: 177.1.58.5
Number of MTID metrics: 0
TOS 0 Metrics: 1
Router Link States (Area 12345)
LS age: 917
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 177.1.5.5
Advertising Router: 177.1.5.5
LS Seq Number: 80000002
Checksum: 0xBFEF
Length: 96
Area Border Router
Number of Links: 6
Link connected to: a Stub Network
(Link ID) Network/subnet number: 170.1.5.5
(Link Data) Network Mask: 255.255.255.255
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 170.1.2.2
(Link Data) Router Interface address: 177.1.0.5
Number of MTID metrics: 0
TOS 0 Metrics: 1000
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 170.1.3.3
(Link Data) Router Interface address: 177.1.0.5
Number of MTID metrics: 0
TOS 0 Metrics: 1000
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 170.1.1.1
(Link Data) Router Interface address: 177.1.0.5
Number of MTID metrics: 0
TOS 0 Metrics: 1000
Link connected to: another Router (point-to-point)
