OSPF Stub Router Advertisement

OSPF allows a router to specify a max-metric so that it can gracefully be removed from the network without having to wait around for timers to expire and the like. This will allow the specified router to update its Type-1 LSA to max metric which will force neighbors to recompute.

Here is a neighbor’s view before hand.

R5#sh ip ospf data router 150.1.4.4

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Router Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 1399
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 150.1.4.4
  Advertising Router: 150.1.4.4
  LS Seq Number: 8000000E
  Checksum: 0x8B9E
  Length: 84
  Area Border Router
  AS Boundary Router
  Number of Links: 5

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 150.1.4.4
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 150.1.5.5
     (Link Data) Router Interface address: 155.1.45.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 155.1.45.0
     (Link Data) Network Mask: 255.255.255.0
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 150.1.5.5
     (Link Data) Router Interface address: 155.1.0.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 155.1.0.4
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 0

Here is the stub router advertisement configuration

router ospf 1
 max-metric router-lsa

Here is the aftermath… Notice that stub networks arent maxed out by default, but can be done by including the include-stub keyword. external LSAs can also be maxed by using the external-lsa keyword.

R5#sh ip ospf data router 150.1.4.4

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Router Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 178
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 150.1.4.4
  Advertising Router: 150.1.4.4
  LS Seq Number: 8000000F
  Checksum: 0x7435
  Length: 84
  Area Border Router
  AS Boundary Router
  Number of Links: 5

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 150.1.4.4
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 150.1.5.5
     (Link Data) Router Interface address: 155.1.45.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 65535

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 155.1.45.0
     (Link Data) Network Mask: 255.255.255.0
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 150.1.5.5
     (Link Data) Router Interface address: 155.1.0.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 65535

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 155.1.0.4
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 0

http://www.cisco.com/en/US/customer/docs/ios/iproute/configuration/guide/irp_ospf_stub_router_ps6350_TSD_Products_Configuration_Guide_Chapter.html

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