OSPF link only as backup?

[pashdown1]

I have the following OSPF setup:

Area 100---(OSPF cost 1000)---Router A---(10Gb link)---Router B----(OSPF cost 0)--Area 100

"Area 100" is the same network and the same router, so this is really one big circle.  I desire to only use the link on Router A if Router B cannot reach "Area 100", yet in spite of playing with the cost of the link on Router A, it remains the only route to "Area 100" Router A knows about.  The area between Router A & B is backbone (0.0.0.0), but the OSPF route for Area 100 are not shared over the 10Gb link.  Other OSPF routes are propagating over the 10Gb link just fine.  Any ideas?

[tobyarnett]

What is the link speed on each connection? Also
Are we assuming there is only the single area of 100 being used in all theses device or are you using multiple areas. For starters though I would modify you reference bandwidth on the A router from 1000 to 1. This should alter the metric used from router A to area 100 with a higher overall cost. When you start altering the cost values then you need to also ensure your math is right on all your links. I am guessing by altering your reference bandwidth on router A to 1000 that will now make your link from A to area 100 preferred.

Please list outside all the link speeds to double check which path is being chosen and why.

Thank you,
Toby

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[paul driver]

Hello Pete,

Have you applied  the auto-cost reference-bandwidth statement to include link speeds higher then 100mb becasue if it isn't  anything over this link speed will be counted as the same cost of a FE interface =1

auto-cost reference-bandwith 10000 

This will set so a Fastethernet link to be counted as 100 -  10000/100=100

res

Paul

[pashdown1]

Toby: Can I set the reference cost on a per link basis?  I couldn't find a command for it.

pdriver:I have set the auto-cost reference-bandwidth to 10000 but it hasn't changed the situation.  Here is some more info:

routerA#show ip route X.X.X.X
Routing entry for X.X.X.X/24
  Known via "ospf 6315", distance 110, metric 1001, type intra area
  Last update from Y.Y.Y.110 on Vlan6, 00:11:12 ago
  Routing Descriptor Blocks:
  * Y.Y.Y.110, from Y.Y.Y.110, 00:11:12 ago, via Vlan6
      Route metric is 1001, traffic share count is 1

routerA#show run int vlan650
interface Vlan6
 ip address Y.Y.Y.109 255.255.255.252
 no ip redirects
 ip ospf network point-to-point
 ip ospf cost 1000
end


routerB#show ip route X.X.X.X
Routing entry for X.X.X.X/24
  Known via "ospf 6315", distance 110, metric 11, type intra area
  Last update from Y.Y.Y.110 on Vlan7, 00:01:08 ago
  Routing Descriptor Blocks:
  * Y.Y.Y.110, from Y.Y.Y.110, 00:01:08 ago, via Vlan7
      Route metric is 11, traffic share count is 1

routerB#show run int vlan7
interface Vlan7
 ip address Y.Y.Y.109 255.255.255.252
 no ip redirects
 ip ospf network point-to-point
end

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

If you have area 0 between two area 100 routers that don't have another intra-area path, you've partitioned OSPF area 100.  If this is what you've done, it might explain the issue you're seeing.

[pashdown1]

Thank you Joseph.

This may be obvious, but can you have overlapping OSPF areas?  Can one subnet or interface be defined as multiple areas?

[tobyarnett]

Pete,

You can not set the cost per link because the cost metric you entered has only modified the default reference bandwidth from 100 to something that can handle higher speed links. You can use the bandwidth statement per link if needed to furher control paths. Listing out your interfaces though would help to understand what routes are being selected.

The issue I am concerned with is if you have an other are a in the middle. Looks like there is from your output. List the link speed per segment and any other areas used.


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[pashdown1]

Link speed on Vlan6 is 10Mbit, Vlan7 is 100Mbit.  Regardless of the link speed, the customer would rather only have traffic over Vlan6 if Vlan7 is down.  That means 0 the rest of the time.

The 10Gbit area is 0.0.0.0.  Can I define multiple areas to the same interface or subnet?  I was under the impression that 0.0.0.0 encompassed all areas, but I guess I was wrong.  Is there a way to encompass all areas on a router for a trunk-style backup to a redundant router?

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

The 10Gbit area is 0.0.0.0.  Can I define multiple areas to the same interface or subnet?  I was under the impression that 0.0.0.0 encompassed all areas, but I guess I was wrong.  Is there a way to encompass all areas on a router for a trunk-style backup to a redundant router?

It might be possible to define the same subnet to multiple areas on different routers.  Doing so, I believe, is logically incorrect.

It might be possible to have the same interface in multiple areas if using subinterfaces or secondary addresses, but in such cases you're not really advertising the interface you're advertising different subnets.

Area 0 doesn't really encompass all areas, it does, however, provide the backbone or shared area that all other areas should connect to.  Area 0 should never be partitioned.

Other non zero areas can be partitioned, but it's poor practice and can lead to issues.  For example, if you summarize the same routes leaving an area that the partitioned area doesn't contain.

You can have a router with interfaces in multiple areas, including not having any in area 0, but if you do this, routes in one area are not directly advertised to the other area(s).  If one of the connected areas is area 0, then you've made an area border router (as also noted by Toby).

Your topology isn't clear, at least to me, and there are "rules" for both intra-area and inter-area routing.  This is why I noted such rules can take precedence over normal path costs.

I you could post a simple diagram of your topology, with the redundancy, and the area assignments, that would be very helpful.

[tobyarnett]

Yes you can have multiple areas having overlapping interfaces. This gives you an area border router. This is what you need in the middle if you have another area. Also may want to use the auto-cost of 1000 instead of 10000.


Toby

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[tobyarnett]

Sorry not sure where on your initial diagam vlan 6 or 7 are.

If you want all interfaces advertised I would either list them out individually for security and also because I think it looks cleaner. The alternative is to just do a redistribute connected in each of your ospf processes.

Toby


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[paul driver]

Hello pete,

If you wish to enable ospf on all interfaces and populate into a specific given area, then either

1) enable opsf on each interface -

int xx

ip ospf x area xx

2) use the network command for each interface under the ospf process

router ospf X

network x.x.x.x y.y.y.y area x

3) use a generic network command for all interfaces under the ospf process

router ospf X

nework 0.0.0.0 0.0.0.0 area xxx

4) if you wish to advertised your interfaces as external networks use the residtributed command ( default E2 type) under the ospf process

router ospf X

redistribute connected subnets

res

Paul

[pashdown1]

Here is the current topology of the network in question:

Area 100, Router C---(OSPF cost 1000, 10Mb link, network Y.Y.Y.109)---Router A (6509)---(10Gb link (Area 0.0.0.0))---Router B (6509)----(OSPF cost 0, 100Mb link, network X.X.X.109)--Area 100, Router C

The 10Mb and 100Mb links are connected to the same router, Router C.

Today I tried to add a network statement for area 100 for the 10Gb link.  Instead of adding-on, it overrode the 0.0.0.0 area.  I did this in the "router ospf NNNN" stanza, because it isn't possible for some reason to define "ip ospf x area xx" in the interface.  Bafflingly, I can do it in the interface for "ipv6 ospf x area xx".

How do i define a network or interface to multiple ospf areas?  Segmentation of areas on my core routers (A&B 6509's), connected by the 10Gb link will continue until I'm able to do this.

[tobyarnett]

Pete,

So I hope this is a lab environment that you can test this, because you are not giving too much detail to properly help. So take this advice as it is and just user advice. So with what you have provided I would suggest you do the following introduce another OSPF process to share routes from Area 6509 to Area 100. This should help you propagate routes from Area 100 to your Area 6509 and then you can use your costing metrics to determine the best route out of 6509.

On router C add a router ospf 6509 process. Then in your network statements you can advertise y.y.y.109 and x.x.x.109 in your OSPF process. This will allow Router C to have a routing table with 6509 and 100. This with your costing should allow the best path out of your network to be from Router A to Router C.

From your topology.

Area 100, Router C (add 6509 to this link)---(OSPF cost 1000, 10Mb link, network Y.Y.Y.109)---Router A (6509)---(10Gb link (Area 0.0.0.0))---Router B (6509)----(OSPF cost 0, 100Mb link, network X.X.X.109)—(add 6509 to this link)Area 100, Router C

-Toby

[tobyarnett]

Pete,

Is there any update on your configs and routing status?


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