IP Connectivity Intermediate ~12 min · 3-device

Bring up OSPF on a 3-router triangle

Three routers wired in a triangle (each router connects to both others). All interfaces are already IP'd and up. Configure single-area OSPF (area 0) on all three so every router sees the other two as Full neighbors and learns routes to the remote loopbacks. Then ping across.

R1 Lo0=1.1.1.1 Gi0/0 10.0.12.1/30 ─── 10.0.12.2/30 Gi0/0 R2 Lo0=2.2.2.2
R1 Gi0/1 10.0.13.1/30 ─── 10.0.13.2/30 Gi0/0 R3 Lo0=3.3.3.3
R2 Gi0/1 10.0.23.1/30 ─── 10.0.23.2/30 Gi0/1 R3

Topology

Objectives

○R1 ⇄ R2 Full adjacency
○R1 ⇄ R3 Full adjacency
○R2 ⇄ R3 Full adjacency
○R1 has an OSPF route to 3.3.3.3/32
○Verified with show ip ospf neighbor on any router

Hints

Hint 1, the pattern

On each router: router ospf 1, then a network statement for each interface's subnet (including the loopback), all in area 0.

Hint 2, wildcard mask

Wildcards are the inverse of a netmask. For a /30 (mask 255.255.255.252), wildcard is 0.0.0.3. For a /32 loopback, wildcard is 0.0.0.0.

Hint 3, full sequence

# On R1
enable
conf t
 router ospf 1
  router-id 1.1.1.1
  network 10.0.12.0 0.0.0.3 area 0
  network 10.0.13.0 0.0.0.3 area 0
  network 1.1.1.1 0.0.0.0 area 0
 end
show ip ospf neighbor

# On R2
enable
conf t
 router ospf 1
  router-id 2.2.2.2
  network 10.0.12.0 0.0.0.3 area 0
  network 10.0.23.0 0.0.0.3 area 0
  network 2.2.2.2 0.0.0.0 area 0
 end

# On R3
enable
conf t
 router ospf 1
  router-id 3.3.3.3
  network 10.0.13.0 0.0.0.3 area 0
  network 10.0.23.0 0.0.0.3 area 0
  network 3.3.3.3 0.0.0.0 area 0
 end

Bonus, traceroute + detail views

Once neighbors are Full, try traceroute 3.3.3.3 from R1 (goes via one of R2/R3 depending on cost). Then run show ip ospf neighbor detail to see state changes and Dead timer.

Neighbors reach Full the moment both sides have matching network area 0 statements, engine converges after every command.

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Two routers, static routes, ping across

IP Connectivity · ~10 min

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Configure a DHCP server pool

IP Services · ~6 min

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Bring up OSPF on a 3-router triangle

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