Question about OSPF preferring higher cost route from area0

From: Eric Poulin (epoulins@yahoo.com)
Date: Tue May 22 2007 - 01:04:27 ART

Hi GS,

I have two routers, R4 and R5, running OSPF between each other over Frame Relay (Area0)
and also Ethernet (Area45). R5 is learning an inter-area route 150.1.6.6/32 from R4 over
both links. The OSPF cost to reach R4 over the FR is 64 and Ethernet is 1. Please can
someone explain me why R5 prefers the route over the frame Relay as opposed to the
Ethernet? I was expecting R5 to chose its Ethernet link with a cumulative cost of 3
instead of the FR interface with a cumulative cost of 66? Are routes for the same prefix
preferred within Area0?

Thanks for your help,
Eric

----------------------------
Rack1R5#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
150.1.4.4 0 FULL/DROTHER 868 msec 183.1.0.4 Serial0/0
150.1.4.4 1 FULL/DR 00:01:46 183.1.45.4 FastEthernet0/1
----------------------------
Rack1R5#sh ip route ospf
     150.1.0.0/16 is variably subnetted, 9 subnets, 2 masks
O IA 150.1.6.6/32 [110/66] via 183.1.0.4, 00:05:09, Serial0/0
----------------------------
Rack1R5#sh ip ospf database summ 150.1.6.6

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

                Summary Net Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 1865
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 150.1.6.6 (summary Network Number)
  Advertising Router: 150.1.4.4
  LS Seq Number: 80000012
  Checksum: 0xC323
  Length: 28
  Network Mask: /32
        TOS: 0 Metric: 2

                Summary Net Link States (Area 45)

  LS age: 1865
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 150.1.6.6 (summary Network Number)
  Advertising Router: 150.1.4.4
  LS Seq Number: 80000012
  Checksum: 0xC323
  Length: 28
  Network Mask: /32
        TOS: 0 Metric: 2
----------------------------
Rack1R5#sh ip ospf database 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: 186
  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: 80000018
  Checksum: 0x8AE6
  Length: 48
  Area Border Router
  Number of Links: 2

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 183.1.0.5
     (Link Data) Router Interface address: 183.1.0.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    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

                Router Link States (Area 45)

  Routing Bit Set on this LSA
  LS age: 576
  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: 8000001C
  Checksum: 0x6C97
  Length: 36
  Area Border Router
  Number of Links: 1

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 183.1.45.4
     (Link Data) Router Interface address: 183.1.45.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 1
----------------------------

       

This archive was generated by hypermail 2.1.4 : Fri Jun 01 2007 - 06:55:21 ART