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New Member

Enforced 'dynamic' OSPF cost in Etherchannel

Dear all,

I'm working in a network of Catalyst 4948Es. I want to enforce the ospf cost of a port-channel interface, but at the same time I want the port-channel cost to change when any of the member links fails. If I use commands like 'bandwidth' or 'ip ospf cost' on the port-channel interface the cost remains the same when a link comes down. I thought that maybe changing ospf cost of the members could influence in any way the cost of the port-channel, but it has no impact. Changing the global reference bandwidth is not an option either. At present time the only option I see is using the embeded event manager, but I would be grateful if you could suggest me another way to get this 'dynamically modified' OSPF cost for a port-channel.

Thank you

Octavio

8 REPLIES

Enforced 'dynamic' OSPF cost in Etherchannel

Hi Octavio,

did you configure the port-channel interfaces as a layer 3 interfaces or layer 2 + SVIs?

Regards

Rolf

New Member

Enforced 'dynamic' OSPF cost in Etherchannel

Hi Rolf,

As a layer 3 interface:

interface Port-channel60

vrf forwarding DIST

ip address 10.10.10.5 255.255.255.252

ip pim query-interval 500 msec

ip pim sparse-mode

ip ospf network point-to-point

load-interval 30

carrier-delay msec 0

end

interface GigabitEthernet1/1

no switchport

dampening

load-interval 30

carrier-delay msec 0

channel-group 60 mode active

end

interface GigabitEthernet1/2

no switchport

dampening

load-interval 30

carrier-delay msec 0

channel-group 60 mode active

end

Thanks in advance

Octavio

Re: Enforced 'dynamic' OSPF cost in Etherchannel

Could you please also post a 'show ip ospf interface po60', I'd be interested in the cost for this 2Gig port-channel interface.

Did you increase the OSPF reference-bandwidth (otherwise every link >= FastEthernet will have an OSPF cost of 1) ?

Both member ports are bundled?

Regards

Rolf

New Member

Enforced 'dynamic' OSPF cost in Etherchannel

Hi Rolf,

Both 4948Es have the same outputs, so I send the ones of one of them.

* Reference bw is 1Tbps

C4900A#sh run | i reference

auto-cost reference-bandwidth 1000000

* Both members are GE interfaces, son 1Tbps/2Gbps=500

C4900A#sh ip ospf interface port-channel 60

Port-channel60 is up, line protocol is up (connected)

  Internet Address 10.10.10.1/30, Area 0, Attached via Network Statement

  Process ID 1, Router ID 10.0.0.1, Network Type POINT_TO_POINT, Cost: 500

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           500      no          no            Base

  Transmit Delay is 1 sec, State POINT_TO_POINT

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    Hello due in 00:00:01

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 2/2, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 10.0.0.3

  Suppress hello for 0 neighbor(s)

* Both members are bundled:

C4900A#sh lacp internal       

Flags:  S - Device is requesting Slow LACPDUs

        F - Device is requesting Fast LACPDUs

        A - Device is in Active mode       P - Device is in Passive mode    

Channel group 60

                            LACP port     Admin     Oper    Port        Port

Port      Flags   State     Priority      Key       Key     Number      State

Gi1/1     SA      bndl      32768         0x3C      0x3C    0x3B        0x3D 

Gi1/2     SA      bndl      32768         0x3C      0x3C    0x3C        0x3D 

C4900A#sh lacp internal detail

Flags:  S - Device is requesting Slow LACPDUs

        F - Device is requesting Fast LACPDUs

        A - Device is in Active mode       P - Device is in Passive mode    

Channel group 60

Actor (internal) information:

          Actor                 Actor                       Actor

Port      System ID             Port Number     Age         Flags

Gi1/1     32768,78da.6ecb.9540  0x3B             22s        SA

          LACP Actor           Actor           Actor

          Port Priority        Oper Key        Port State

          32768                0x3C            0x3D

          Port State Flags Decode:

          Activity:   Timeout:   Aggregation:   Synchronization:

          Active      Long       Yes            Yes

          Collecting:   Distributing:   Defaulted:   Expired:

          Yes           Yes             No           No

          Actor                 Actor                       Actor

Port      System ID             Port Number     Age         Flags

Gi1/2     32768,78da.6ecb.9540  0x3C              1s        SA

          LACP Actor           Actor           Actor

          Port Priority        Oper Key        Port State

          32768                0x3C            0x3D

          Port State Flags Decode:

          Activity:   Timeout:   Aggregation:   Synchronization:

          Active      Long       Yes            Yes

          Collecting:   Distributing:   Defaulted:   Expired:

          Yes           Yes             No           No

Thanks a lot. I really appreciate your help.

Regards

Octavio

Re:Enforced 'dynamic' OSPF cost in Etherchannel

Octavio,

you're welcome.
From what I see, everything looks like expected.
I'd assume that the cost increases to 1000 when one of the member-ports unbundles? Would that solve your reqirements?

HTH
Rolf

Sent from Cisco Technical Support Android App

New Member

Enforced 'dynamic' OSPF cost in Etherchannel

Hi Rolf,

It's as you described. If I shut down one GE interface, the cost is 1000.

The point is that I would like to go one step beyond. I would like to have a cost for the same port-channel of 4000 and, if one GE fails, I want it to be 8000. I tried several things:

* "ip ospf cost 4000" on the port-channel. If one GE comes down, the cost remains the same

* "ip ospf cost 8000" on both GE members. It has no impact on the cost of the port-channel, as it is 500

* "banwidth 250Mbps" on both GE members to get a cost of 4000 per link. It has no impact on the cost of the port-channel, as it is 500

I can not change the cost of the port-channel and, at the same time, keep its dependancy with the number of active member links.

The only option I find is making a script with the Embedded Event Manager to track both GE members and, if one fails, change the cost of the port-channel.

Thank you

Octavio

Enforced 'dynamic' OSPF cost in Etherchannel

Octavio,

o.k., now I understand. Sorry for beeing somewhat slow-witted.

Perhaps somebody else can provide a solution, but I think you've already tried everything possible with standard-IOS.

If the all-or-nothing approach of the port-channel min-links command is no option, I'd also use EEM to solve this.

The EC-5-BUNDLE/UNBUNDLE syslog messages look promising to trigger an applet/script.

Regards

Rolf

New Member

Enforced 'dynamic' OSPF cost in Etherchannel

Thank you very much, Rolf. I really appreciate your guidance to verify that everything was as it should be. Thanks a lot for the syslog message to track, too. Really useful.

Thanks a lot

Octavio

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