Re: route selection when forwarding address is non zero

What is the forward metric on those routes (cost to reach ABR / FA (if
non-zero))? Remember that FA is an IP address and as such it is associated
with an interface. As such it may have a higher cost than the cost to reach
the ABR. When you remove the FA, you're effectively lowering the cost of
route.

To see what I'm talking about, the easiest way is to convert the metric to
E1 and compare the metrics. You can also see the forward metric by running
"show ip route x.x.x.x" instead of "show ip route ospf", which will show
you only external metric.

--
Marko Milivojevic - CCIE #18427 (SP R&S)
Senior CCIE Instructor / Managing Partner - IPexpert
On Sat, Sep 14, 2013 at 5:33 AM, Imran Ali <immrccie_at_gmail.com> wrote:
> i  have  a senario in  which forwarding address is non zero
>
> router picks  route  via this non zero forwarding address , even though it
> has same e
> equal cost route.
>
> when i change FA  to zero ( 0.0.0.0)  by changing network type , then
> routing table adds  other  equal cost route.
>
> R1#show ip route ospf
>      151.90.0.0/24 is subnetted, 4 subnets
> O E2    151.90.103.0 [110/20] via 151.90.163.3, 00:00:01, Ethernet0/0
> R1#
>
>
> R1#show ip ospf database external
>
>             OSPF Router with ID (151.90.163.1) (Process ID 1)
>
>                 Type-5 AS External Link States
>
>   Routing Bit Set on this LSA
>   LS age: 10
>   Options: (No TOS-capability, DC)
>   LS Type: AS External Link
>   Link State ID: 151.90.103.0 (External Network Number )
>   Advertising Router: 151.90.163.6
>   LS Seq Number: 80000003
>   Checksum: 0xF719
>   Length: 36
>   Network Mask: /24
>         Metric Type: 2 (Larger than any link state path)
>         TOS: 0
>         Metric: 20
>         Forward Address: 151.90.163.3
>         External Route Tag: 0
>
>
>
>
> R1(config)#int Ethernet0/0
> R1(config-if)#ip ospf network point-to-point
>
>
>
>
> R1#show ip ospf database external
>
>             OSPF Router with ID (151.90.163.1) (Process ID 1)
>
>                 Type-5 AS External Link States
>
>   Routing Bit Set on this LSA
>   LS age: 553
>   Options: (No TOS-capability, DC)
>   LS Type: AS External Link
>   Link State ID: 151.90.103.0 (External Network Number )
>   Advertising Router: 151.90.163.6
>   LS Seq Number: 80000004
>   Checksum: 0xBCEB
>   Length: 36
>   Network Mask: /24
>         Metric Type: 2 (Larger than any link state path)
>         TOS: 0
>         Metric: 20
>         Forward Address: 0.0.0.0
>         External Route Tag: 0
>
> R1#show ip ospf border
> R1#show ip ospf border-routers
>
> OSPF Process 1 internal Routing Table
>
> Codes: i - Intra-area route, I - Inter-area route
>
> i 151.90.163.6 [10] via 151.90.163.6, Ethernet0/0, ASBR, Area 0, SPF 18
> i 151.90.163.6 [10] via 151.90.16.6, Ethernet0/1, ASBR, Area 0, SPF 18
> R1#
>
> O E2    151.90.103.0/24 [110/20] via 151.90.163.6, 00:00:15, Ethernet0/0
>                         [110/20] via 151.90.16.6, 00:00:15, Ethernet0/1
>
>
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