Advice regarding OSPF areas

[mmendis]

Hi All,

I need a advice regarding the OSPF areas. My issue is as follows.

Requirement :-

Client 01 need to access Client 03

Observations :-

Client 01 --> R1 --> R2 --> R3 --> R10 --> R9 --> R8 --> Client 03

R3 & R7 are ABR

Possible less HOP path :-

Client 01 --> R1 --> R2 --> R4 --> R7 --> R8 --> Client 03

* What ever the cost I have set it always take the longest path.  How can I change it to shorter path I have mentioned above ?

[paul driver]

Hello

Quick, simple but elegant solution would be to apply a maximum metric for the less preferred ABR, This will apply a costing for of 65k+ as a result client 1 should take R4 (ABR) towards client 3.

(note: this would affect all traffic to from client 1 -3)

R3(ABR)
router ospf x
max-metric summary-lsa

res

Paul

[mmendis]

Thanks Paul for the quick response....
I have created a test lab to simulate the same incident and I have set the value in R3.
Following is the result I got from the R2 router. ( Please note 5.5.5.5 is the loopback IP of R8 && 10.10.2.2 is R3 ABR router )

R2>show ip route 5.5.5.5
Routing entry for 5.5.5.5/32
Known via "ospf 10", distance 110, metric 16711690, type inter area
Last update from 10.10.2.2 on Ethernet0/1, 00:03:22 ago
Routing Descriptor Blocks:
* 10.10.2.2, from 10.10.3.1, 00:03:22 ago, via Ethernet0/1
Route metric is 16711690, traffic share count is 1

[paul driver]

Hello

can you confirm:

1)you have resiliency via R4-R7 from both the ABR's -
2) R2 is the DR for both R3-R4
3) applied  max-metric router-lsa summary-lsa on ABR R3
4) post the output of the following from either ABR after before and after max-metric has been applied.

sh ip ospf database summary adv-router (r3 rid x.x.x.x) | be  5.5.5.0
sh ip ospf database summary adv-router (r7 rid x.x.x.x) | be  5.5.5.0

res
Paul

[mmendis]

(1) Am not sure about the question. But as I understood ... R3 && R7 are ABRs and has connectivity via R4

(2)Yes

(3) Applied

(4) This is after applying the command.

R3#sh ip ospf database summary adv-router 10.10.3.1 | be 5.5.5.5
  Link State ID: 5.5.5.5 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002A
  Checksum: 0x8A5D
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 6.6.6.6 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x5A88
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 7.7.7.7 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x2CB2
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.3.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x41A5
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.4.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x36AF
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.5.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x2BB9
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.6.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x20C3
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680


                Summary Net Link States (Area 40)

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 1.1.1.1 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0x49B1
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 2.2.2.2 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0x1BDB
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 3.3.3.3 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0xEC06
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 4.4.4.4 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0xBE30
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.1.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0x5F8D
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.2.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0x6682
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 16711680

  Exception Flag: Announcing maximum metrics for topology Base with MTID 0
  LS age: 523
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.7.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000027
  Checksum: 0x1DC9
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 16711680

This is without the Metric command

R3#sh ip ospf database summary adv-router 10.10.3.1 | be 5.5.5.5
  Link State ID: 5.5.5.5 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002B
  Checksum: 0x5978
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65556

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 6.6.6.6 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0xC412
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65546

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 7.7.7.7 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0x32AA
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65536

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.3.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0x3FA6
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65535

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.4.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0x9644
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65545

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.5.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0xEFDF
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65555

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.6.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 8000002C
  Checksum: 0x497B
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65565


                Summary Net Link States (Area 40)

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 1.1.1.1 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0xB33B
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65546

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 2.2.2.2 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0x21D3
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65536

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 3.3.3.3 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0xF4FB
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 1

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 4.4.4.4 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0xC428
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 65536

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.1.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0xBF22
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65545

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.2.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0x6483
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 65535

  LS age: 5
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.7.0 (summary Network Number)
  Advertising Router: 10.10.3.1
  LS Seq Number: 80000028
  Checksum: 0x7D5E
  Length: 28
  Network Mask: /30
        MTID: 0         Metric: 65545

[Georg Pauwen]

Paul,

the max-metric summary-lsa works great for ABR preference, didn't know about that one...good stuff !

[Georg Pauwen]

Hello,

how is R2 conected to R3 and R4 ?

[mmendis]

Thanks for the reply Georg,
R2 , R3 & R4 connected via Switch which use the same subnet IPs.....

[Georg Pauwen]

Hello,

I am going to lab this, in the meantime, try and define neighbors on R3 with a different cost:

R2

neighbor R4 cost 100

neighbor R3 cost 500

[Georg Pauwen]

Hello,

so I have recreated your setup is GNS3.  If you set the links connecting R2, R3, and R4 to 'ip ospf network non-broadcast' you can set the cost for both neighbors on R2:

R2

neighbor 3.3.3.3 cost 700

neighbor 4.4.4.4 cost 100

With this setup, R4 (id 4.4.4.4) will now be the preferred route, as it has a lower cost...

[paul driver]

Hello

@Georg Pauwen
Given the current topology this should work irrespective of changing the opsf network type on the Multi-point connections between R2,R3 and R4,
Given that you have got this setup in GNS, Would you also be able you confirm the query's I have raised please as they would be interesting to see.

res

Paul

[Georg Pauwen]

Paul,

In GNS3, I indeed did not have to change anything to have R4 as the preferred path. I am not sure why R3 is preferred in OP's lab, for that I guess we would have to see the full configs. Setting the cost solves the problem, but you are right, the problem shouldn't be there in the first place...

[paul driver]

Hello Gerog

TBH - I am more interested in the finding the problem then an alternative solution to what I posted at this time

Would you be able confirm with that gns setup you have did the max-metric summary work or not?

Were interfaces between R2-R3_R4 already OSPF non broadcast or Broadcast type, As in the OP it suggest it was the latter?

Much appreciated Gerog 

Paul

[Georg Pauwen]

Paul, 

with all interfaces at their default (broadcast), your solution seems to work. However, I am setting the command 'max-metric router-lsa' on R4, so I can check if the preferred path changes to R3. I cannot implement it on R3, because R3 is not the preferred path,  as in OP's lab.

Hope that makes sense. I don't know how R3 can be the preferred path to start out with. Seeing the configs of OP's original lab would help...

[paul driver]

Hello

thank for your input - yes it will be interesting to obtain some feedback from mmendis 

it may be the path via R4 isn’t valid at all meaning the route isn’t even being advertised that way!

thanks once again for the feedback

very much appreciated 

res

paul