[c-nsp] OSPF Default Route Injection

[David Granzer]

Hi,

I have test setup with three routers R2/R3/R4, they running OSPF, R2
and R3 injecting default with "default-information originate always
metric 20", R4 already sees default route from both

R4#sh ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
  Known via "ospf 2", distance 110, metric 20, candidate default path
  Tag 2, type extern 2, forward metric 10
  Last update from 10.0.0.13 on FastEthernet0/1, 00:01:26 ago
  Routing Descriptor Blocks:
  * 10.0.0.13, from 150.0.0.3, 00:01:26 ago, via FastEthernet0/1
      Route metric is 20, traffic share count is 1
      Route tag 2
    10.0.0.9, from 150.0.0.2, 00:01:26 ago, via FastEthernet0/0
      Route metric is 20, traffic share count is 1
      Route tag 2

but R2 doesn't have default route from R3 installed in routing table
and vice versa. R2 and R3 sees external LSA from each other but
without Routing Bit set.

R3#sh ip route 0.0.0.0
% Network not in table

R3#sh ip ospf data ex 0.0.0.0

            OSPF Router with ID (150.0.0.3) (Process ID 2)

                Type-5 AS External Link States

  LS age: 484
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 0.0.0.0 (External Network Number )
  Advertising Router: 150.0.0.2
  LS Seq Number: 80000001
  Checksum: 0xB451
  Length: 36
  Network Mask: /0
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 2

  LS age: 482
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 0.0.0.0 (External Network Number )
  Advertising Router: 150.0.0.3
  LS Seq Number: 80000001
  Checksum: 0xAE56
  Length: 36
  Network Mask: /0
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 2


Best Regards,
David


On Thu, Mar 18, 2010 at 6:34 PM, Kevin Hatem <Kevin.Hatem at pgs.com> wrote:
> If two routers are injecting a default route under OSPF then each router will retain their own default route in the route table as each other's injected default route has the same distance as its self advertised default.  You could set a higher/lower distance on inbound advertisements from the neighbors to influence the installation of the default route into the RIB.
>
> HTH
> -kevin
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of David Granzer
> Sent: Thursday, March 18, 2010 09:13
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] OSPF Default Route Injection
>
> Hello,
>
> please could someone explain what exactly command "default-information
> originate always" under ospf process works ?  When you have more than
> one router configured with this default route injection is correct
> behavior that you don't see on these routers default route in their ip
> routing table from other routers and you see only external lsa for
> 0.0.0.0 in ospf database ?
>
> Thanks,
> David
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>
> This e-mail, including any attachments and response string, may contain proprietary information which is confidential and may be legally privileged. It is for the intended recipient only. If you are not the intended recipient or transmission error has misdirected this e-mail, please notify the author by return e-mail and delete this message and any attachment immediately. If you are not the intended recipient you must not use, disclose, distribute, forward, copy, print or rely on this e-mail in any way except as permitted by the author.
>
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>