question about ospf default information originate metric !!

[Dr.X]

i have  topology worjing with ospf routing protocol

R1(Asbr)-----SWITCH --------R2

R1 configs:

==========================

!       

router ospf 1

router-id 1.1.1.1

default-information originate metric-type 1

!       

no ip http server

no ip http secure-server

!       

ip classless

ip route 0.0.0.0 0.0.0.0 176.66.66.1

!       

!       

!       

!       

control-plane

!       

!       

=================

R1 is reditributing into ospf ,

now on R5 , why the metric is 3 ,  why it is not 2 ????????

===============================

R5#sh ip route

O*E1 0.0.0.0/0 [110/3] via 192.168.40.1, 00:40:23, FastEthernet0/0

======================================================================

R5#SH IP OSpf Database External

            OSPF Router with ID (5.5.5.5) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA

  LS age: 580

  Options: (No TOS-capability, DC)

  LS Type: AS External Link

  Link State ID: 0.0.0.0 (External Network Number )

  Advertising Router: 1.1.1.1

  LS Seq Number: 80000002

  Checksum: 0xDE4

  Length: 36

  Network Mask: /0

        Metric Type: 1 (Comparable directly to link state metric)

        TOS: 0

        Metric: 1

        Forward Address: 176.58.79.2

        External Route Tag: 1

======================================

R5#SH IP OSpf Database ASbr-summary

            OSPF Router with ID (5.5.5.5) (Process ID 1)

                Summary ASB Link States (Area 4)

  LS age: 1018

  Options: (No TOS-capability, DC, Upward)

  LS Type: Summary Links(AS Boundary Router)

  Link State ID: 1.1.1.1 (AS Boundary Router address)

  Advertising Router: 5.5.5.5

  LS Seq Number: 80000002

  Checksum: 0xBE63

  Length: 28

  Network Mask: /0

        TOS: 0  Metric: 1

=====================================

R5#sh ip ospf interface f

R5#sh ip ospf interface fastEthernet 0/0

FastEthernet0/0 is up, line protocol is up

  Internet Address 192.168.40.5/24, Area 0

  Process ID 1, Router ID 5.5.5.5, Network Type BROADCAST, Cost: 1

  Transmit Delay is 1 sec, State DROTHER, Priority 1

  Designated Router (ID) 3.3.3.3, Interface address 192.168.40.3

  Backup Designated router (ID) 4.4.4.4, Interface address 192.168.40.4

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    Hello due in 00:00:09

===============================================

as u see the cost of R5 interface is 1 ,

AS you see above , the cost to asbr is 1 , and the metric source of type 5 is 1 ,

so why R5 put the cost 3 in the routing table ?????

regards

[Reza Sharifi]

Hi,

Where is r5 located?  Can you post a diagram of the network with all the devices?

[Giuseppe Larosa]

Hello Ahmed,

the LSA type 5 for 0.0.0.0/0 originated by R1 has the forwarding address set:

>> Forward Address: 176.58.79.2

May you post on R5 show ip route 176.58.79.2 ?

My guess is that the different metric is because of the forwarding address that is seen as a sort of next-hop to the external route.

If forwarding address was 0.0.0.0 = ASBR self then the total metric would be 2 as you expect.

In this case with the forwarding address set the metric may be the result of seed metric + metric to the forwarding address

Hope to help

Giuseppe

[Dr.X]

hi ,

Giuseppe,

u may be right ,

here is my topology which im working in

http://www2.0zz0.com/2012/09/22/18/471819576.png

plz give me more detail about my issue

regards

[Dr.X]

R5#sh ip route 176.58.79.2

Routing entry for 176.58.79.0/30

  Known via "ospf 1", distance 110, metric 2, type inter area

  Last update from 192.168.40.1 on FastEthernet0/0, 00:52:51 ago

  Routing Descriptor Blocks:

  * 192.168.40.1, from 1.1.1.1, 00:52:51 ago, via FastEthernet0/0

      Route metric is 2, traffic share count is 1

R5#

[Giuseppe Larosa · Accepted solution]

Hello Ahmed,

my guess is confirmed

Routing entry for 176.58.79.0/30

  Known via "ospf 1", distance 110, metric >>> 2<<<<<<, type inter area

The forwarding address has to be known via an internal route to have the external route installed and the metric to the FA is 2 so total metric to 0.0.0.0/0 becomes 3.

see the following document about OSPF FA effects

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080124c7d.shtml

Hope to help

Giuseppe

[Dr.X]

appreciate ur help ,

i modifies the default route with  null 0 destination instaed of next hop ip ,

and the metric wascorrected to 2 ,

thanks for notifiying about notifying about this trick

regards