FB DISCUSSIONS: HSRP: ENABLING TRACKING ON LAN PORT


Sumit Sharma

November 6 at 8:42pm

—————————-
HSRP: little tricky, but basic
—————————-
Is there any benefit of tracking LAN port on the HSRP member, give logic with your answer
—————————–

Like ·

  •  
    Dicky Wong You can treat yourself as an ISP so that customers ‘ WAN = your LAN
  •  
    Sumit Sharma Different angle .. to think
  •  
    Sumit Sharma Let us suppose, I am in a data center. LAN port which carries traffic from data centre. Is there benefit of tracking LAN port.
  •  
    Pankaj Bandewar Keep a lives packets goes from there and if missed up to hold down timer then hard work
  •  
    Pankaj Bandewar Then stand by become active
  •  
    Sumit Sharma Absolutely right
  •  
    Sumit Sharma But will I get any benefit if I enable tracking on LAN port, any advantage, in terms of mechanism.
  •  
    Dicky Wong Maybe you can treat it’s globalise , 1 dc in apac, 1 in Emma, problem in APAC than goes to Emea, once apac came up, modify the premption again manually
     
    • Sumit Sharma One example topology: R1 & R2, both are present for redundancy. R1 is connected to R2, ibgp is running. By enabling tracking on R1 interface going to R2, is there any advantage ?
    •  
      Dicky Wong Honestly if you have ibgp, you should have ebgp, and no one would like to use harp as a core redundancy semi routing protocol
    •  
      Dicky Wong And in live, every topology must have multiple routing protocols
    •  
      Sumit Sharma thats true, BGP can converge by itself, in case of any failure, but even then for division of LAN traffic, we have HSRP.
    •  
      Sumit Sharma This is the question asked in one of the interviews, may its not that practical approach or something, this may be hypothetical scenario, but even then we should always have some logical reason for scenarios, so thinking in thatdirection.
    •  
      Praveen Rai i don’t think tracking a LAN port matter or i would say needed here as we have HSRP timers and priority also preempt we achieve fast switch over to standby,but yes by track we could achieve bit more granular control like delay if there is flap between link we could take advantage of delay to make HSRP process stable in between we track down flap links
    •  
      Sumit Sharma But point is LAN port goes down, which is also providing layer 2 connectivity between HSRP members, then there are no exchange of Hello packets, there is no priority comparison, both becomes Active.
    •  
      Sumit Sharma But by enabling tracking on LAN port, can we avoid above situation.
       
      •  
        Sumit Sharma But even then, after enabling tracking, priority will be decreased, then we need comparison of priority of HSRP members, for that also we need Layer 2 connectivity. Which is down in our scenario.
      •  
        Sumit Sharma Arpan Sarkar .. bro .. take a look & comment .. this has been asked to someone in interview.
      •  
        Praveen Rai Sumit Sharma buddy build one small topology based on your query then we get clear picture and try to understand problem and possible solutions for it
      •  
        Sumit Sharma Praveen Rai .. Actually, there is no particular topology of LAN to be discussed. you can come up with your LAN topology & solution. we need to justify the above tracking concept, applied to the LAN port in the topology.
      •  
        Sumit Sharma i will come up with some basic diagram also.
      •  
        Himanshu Sharma Refrain your question with new answer : Yes, tracking is not mandatory feature, only recommended. If still you want to track local interface then should use v2 instead of HSRPv1. Because v2 will track actual physical interface not VIP.
      •  
        Arpan Sarkar The question that is coming in my mind is, who is the idiot asking this types of illiterate questions in an interview? When you do not have the layer 2 connectivity between the hsrp speakers then how could ever track work? Hsrp itself will stop working, and both of the hsrp speakers will treat themselves as active. So any benefit of tracking? That scenario happens in case there is no track in the lan interface as well. So again, any benefit if tracking it? In my so called knowledge I don’t have any answers.
      •  
        Himanshu Sharma But how about Layer-3 connectivity tracking….if Layer-2 connectivity is already there…
      •  
        Himanshu Sharma Frankly speaking I did not read all comment, just consider the question only and thought “LAN port” which is member of HSRP is of course assigned with IP Address.
      •  
        Arpan Sarkar Yes sir..it is assigned..but the thing is the links that are connecting hsrp speakers, they exchange hellos over the link. Correct? Now, tracking that link, does it makes sense? If one of the port goes down then hsrp hellos exchange are broken. Now how could tracking comes into play here? Then and there both routers will be active.Correct me if I am wrong
      •  
        Himanshu Sharma Correct but hello packet exchanges VIP address only in HSRP v1 not physical address. If you really want to track physical interface without any commands or special feature simply use HSRP v2. It is by default feature of HSRPv2 “Hello Packets” that it will carry physical interface IP Address not VIP Address and automatically tracking will start.
      •  
        Himanshu Sharma Again I am not talking about benefit of tracking, I am talking how tracking can implement easily. The requirement could be anything or may be that’s what invented by Cisco.
      •  
        Arpan Sarkar Ohh yes..that is correct. My intention lies to the question asked..
      •  
        Sumit Sharma Arpan Sarkar .. bro .. it happens .. number of times .. we have been asked hypothetical situation, sometimes to find out if we really know about something which is quite obvious AND sometimes our knowledge is limited, question is asked purposefully to explore more.
        •  
          Sumit Sharma Think of one LAN topology.
        •  
          Sumit Sharma Two routers, R1 & R2 present in a datacenter for redundancy. Suppose R1 & R2, are connected to each other directly as well as through a common switch also, present in LAN.
        •  
          Sumit Sharma Is it useful or logical to track any of the LAN interface here. If we have Hello packets travelling from common switch connectivity, can we track R1 interface , which is directly connecting to R2.
        •  
          Arpan Sarkar That’s what I explained above.. The answer is N & O. That means NO. See, what would u achieve by tracking it? Suppose the switch goes down. Now how would the other router or this router know that whose link is down? Bcoz both will never receive hello from each other. And on that point both will become active. So this can be achieved without tracking as well. So there is no point of tracking the lan interface. Hello packets itself are tracking it. No need to track it again.
        •  
          Sumit Sharma In case, switch don’t go down, switch is up, only physical interface of R1 directly connecting to R2 goes down.
        •  
          Sumit Sharma FIRST SCENARIO: if we have only one point of connectivity between routers, R1 & R2, which is carrying Hello packets also, absolutely, there is no point of enabling tracking on LAN port.
          •  
            Sumit Sharma SECOND SCENARIO: If we have more than one point of connectivity between R1 & R2, One connectivity is the direct physical connectivity (iBGP is also running on direct physical connectivity), second connectivity is the connectivity through a Layer 2 switch present in the LAN just next to the R1 & R2. Topology is similar to attached photo.

            Sumit Sharma's photo.
          •  
            Sumit Sharma In second scenario, we are discussing if direct connectivity between R1 & R2 goes down. But, second connectivity through Layer 2 switch is up, which can provide Hello Packets for communication. Is it logical or beneficial any how, to track R1 & R2 direct physical connectivity.
          •  
            Arpan Sarkar So now, again, use of it? No use. If link goes down, hsrp itself will track the same. Moreover how many interfaces you will configure hsrp? Means directly connected interface as well as interface connecting to switch? Which again leads to question, how. Bcoz you can use a single ip in a single subnet in the interface. So here if you configure 2 standby ips for 2 interfaces then what will be the default gateway? So it’s absolutely a dull question. There is no use of tracking lan interface.
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s