Task 7.4 - Shaved a few commands off

The task needs us setting up load balancing to 70% and 30%. My setup was:

R4:


 glbp 0 ip 129.1.45.6
 glbp 0 priority 101
 glbp 0 preempt
 glbp 0 weighting 30
 glbp 0 load-balancing weighted

R5:


 glbp 0 ip 129.1.45.6
 glbp 0 weighting 70

The forwarder will be R4 due to the higher priority. Only R4 ever needs to pre-empt as if it's not there, R5 kicks in, if it is there it'll pre-empt. Load balancing is decided by the forwarder based on received weightings reported by each node. Thus R4 is the only one who needs load balancing command right? 

I've only briefly looked into this. My intention isn't to nit pick, but it's good to understand why you're putting the command in. If a command has no affect on anything, then why use it?

 

I may be wrong in the config, which will negate my entire argument. if so, let me know! :)

Comments

  • Hi Beefheadboy,

        Yes indeed the preeemption is needed only on the router with higher priority to preeempt on becoming the AVG. The second statement in the task, requires actually to use "weighted" load-balancing; if you do not configure it, default is "round-robin". You need the command on both routers, for the case when R5 is the AVG.

    Regards

  • The second statement in the task, requires actually to use "weighted" load-balancing; if you do not configure it, default is "round-robin". You need the command on both routers, for the case when R5 is the AVG.

    Cristian, I would not agree with you.

    I did exactly the same configuration as beefheadboy.

    The logic is - R5 cannot be AVG while R4 is up and running (lower priority), if R4 is down, there is no difference what load-balancing method is configured on R5 - it's the only router left.

    The question is, if cisco would accept this logic on CCIE LAB exam.

     

     

  • Cristian - so configuring just "weighting" in both routers are not going to make the routers load balance the traffic you need  "preempt" in there to make it happen?? interesting.

    Another question from this task's last point  "R4 should respond to ARP requests sent by client on VLAN45", which part of the SG take cares of this, Is it "glbp 1 priority 50" in R5? By configuring this in R5 and R4 gets default 100 and starts responding to ARP requests? Is my understanding correct?

  • Cristian - so configuring just "weighting" in both routers are not going to make the routers load balance the traffic you need  "preempt" in there to make it happen?? interesting.

    yes that is coorect and preemption is enabled by default in glbp.

    Another question from this task's last point  "R4 should respond to ARP requests sent by client on VLAN45", which part of the SG take cares of this, Is it "glbp 1 priority 50" in R5? By configuring this in R5 and R4 gets default 100

    The router which has the higher proiority i.e R4 will reply to the client arp request by giving the mac address of R5 and R4 to the clients in the ratio of 70:30

  • with glbp there are 2 pre-emption scenarios.

     

    for ARP replies pre-emption is disabled by default.

     

    for forwarder pre-emption is enabled by default.

     

    ie look at the following out put from R5 f0/1:

    Rack1R5#sh glbp
    FastEthernet0/1 - Group 45
      State is Standby
        1 state change, last state change 00:12:04
      Virtual IP address is 129.1.45.6
      Hello time 3 sec, hold time 10 sec
        Next hello sent in 1.952 secs
      Redirect time 600 sec, forwarder timeout 14400 sec
      Preemption disabled                   <-------------------------------------- ARP pre-emption disabled
      Active is 129.1.45.4, priority 150 (expires in 7.828 sec)
      Standby is local
      Priority 100 (default)
      Weighting 70 (configured 70), thresholds: lower 1, upper 70
      Load balancing: weighted
      Group members:
        c204.14b8.0000 (129.1.45.4)
        c205.14b8.0001 (129.1.45.5) local
      There are 2 forwarders (1 active)
      Forwarder 1
        State is Listen
        MAC address is 0007.b400.2d01 (learnt)
        Owner ID is c204.14b8.0000
        Time to live: 14397.824 sec (maximum 14400 sec)
        Preemption enabled, min delay 30 sec           <------------------------------------ forwarder pre-emption
        Active is 129.1.45.4 (primary), weighting 30 (expires in 8.552 sec)
      Forwarder 2
        State is Active
          1 state change, last state change 00:12:03
        MAC address is 0007.b400.2d02 (default)
        Owner ID is c205.14b8.0001
        Preemption enabled, min delay 30 sec          <------------------------------------ forwarder pre-emption
        Active is local, weighting 70
    Rack1R5#

    Rack1R5#sh run int f0/1
    Building configuration...

    Current configuration : 224 bytes
    !
    interface FastEthernet0/1
     ip address 129.1.45.5 255.255.255.248
     ip pim sparse-mode
     ip ospf mtu-ignore
     duplex auto
     speed auto
     mpls ip
     glbp 45 ip 129.1.45.6
     glbp 45 weighting 70
     glbp 45 load-balancing weighted
    end

  • This was my exact logic while doing this task.

    I did exactly the same configuration as beefheadboy.

    The logic is - R5 cannot be AVG while R4 is up and running (lower priority), if R4 is down, there is no difference what load-balancing method is configured on R5 - it's the only router left.

    The question is, if cisco would accept this logic on CCIE LAB exam.

     

     

     

  • The question doesn't mention applying the preempt command so I didn't put it in.  This only applies to the AVG because the default is not to do so.

    For the AVF the default is to preempt, otherwise I agree with beefheadboy and you don't need it on R5 eitherway.

    Confusing and I hope the question is clearer in the exam.

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