Re: route selection when forwarding address is non zero

http://blog.ipexpert.com/2009/11/11/ospf-type-4-lsa-the-forward-address-part-2/

Joe did a good job explaining above, If its a lab scenario, would you mind
posting your scenario with individual link metrics ?

On Sat, Sep 14, 2013 at 10:24 PM, Marko Milivojevic <markom_at_ipexpert.com>wrote:

> 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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Received on Sun Sep 15 2013 - 00:36:37 ART