Subject: draft-kou-ospf-immediately-replying-hello-00.txt

From: Acee Lindem <[email-masked]>
Date: Fri, 17 Feb 2006 16:17:42 -0500

Hi Zengjie,

Under what situations does having the router who changed to/from
DR/BDR improve convergence (section 6.2)? Since DR/BDR election
is a distributed algorithm dependent on the calculating routers state, it
seems this won't help in all that many cases.

Thanks,
Acee

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From: Zengjie Kou <[email-masked]>
Date: Mon, 20 Feb 2006 11:14:47 +0800

Hi,Acee,
    If a router interface whose role is changed(e.g.DR goes down), the router will notify all routers about the change by immediate hello.
 After all router get the change, election will be reprocessed. In contrast to normal hello, immediate hello avoid the backupSeen.
 Namely, improving convergence.

Thanks a lot,
Zengjie

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From: Acee Lindem <[email-masked]>
Date: Mon, 20 Feb 2006 10:15:28 -0500

Hi Zengjie,

>    If a router interface whose role is changed(e.g.DR goes down), the router will notify all routers about the change by immediate hello.
This is only when the DR/BDR knows that it is going down or the case 
where the router
priority is set to 0.

For a router becoming DR/BDR, all the routers should elect the same DR/BDR
so I don't see how it helps.

Thanks,
Acee

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From: Zengjie Kou <[email-masked]>
Date: Tue, 21 Feb 2006 20:43:09 +0800

Hi, Acee,
    You are right, immediate hello does not provide the mechanism of detecting link down fast. But, immediate hello improve to discover neighbors when interface goes down then up. In practice, the requirement is needed.

Thanks,
Zengjie

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From: Acee Lindem <[email-masked]>
Date: Wed, 22 Feb 2006 16:41:47 -0500

Hi Zengjie,

Speaking strictly in terms of state machines, it seems the interface 
would lose it's DR/BDR state
when it goes down (and cannot send a hello). Wouldn't this scenario be 
better handled
by the empty hello many OSPF implementations send when an interface 
first comes up?

Thanks,
Acee

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From: Zengjie Kou <[email-masked]>
Date: Fri, 24 Feb 2006 17:56:35 +0800

Hi, Acee
   The empty hello mechanism that you refered is adopted by most OSPF implementations indeed when an interface first comes up.
I agree this. However, when an normal interface whose state is up goes down then up, immediate hello  is  effective by avoiding 
helloInterval or backupSeen.

Thanks,
Zengjie

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From: Acee Lindem <[email-masked]>
Date: Fri, 24 Feb 2006 09:10:03 -0500

Hi Zengjie,

I don't think there should be a distinction between first coming or 
coming back up.

Thanks,
Acee

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From: Zengjie Kou <[email-masked]>
Date: Tue, 28 Feb 2006 11:43:51 +0800

Hi, Acee
    On p2p networks, there is no distinction between first coming or coming back up. The immediate hello is efficient in discover neighbors and convergence.
    On broadcast networks, when an interface first coming, DR election need to wait  wait-time. However, when an interface coming back up, DR election need not to wait wait-time(if BDR exists or the down interface is not DR). Here, only HelloInterval or     BackupSeen is needed to discover neighbor or convergence. Immediate hello avoids the HelloInterval or backupSeen on the case.

Thanks,
Zengjie

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From: Acee Lindem <[email-masked]>
Date: Tue, 28 Feb 2006 07:34:44 -0500

Hi Zengjie,

I think you're saying the hello when the DR/BDR interface state changes 
is solely for
the case when the BDR's interface flaps. Correct?

     BDR Interface goes down
     Ex-BDR Interface comes back up
     Ex-BDR send initial hello ----------------------------> Other 
Routers on LAN
     Ex-BDR goes to 2-way <----------------------------   Other Routers 
Immediate reply
                                                                                          
New DR/BDR election
     Triggers election on  Ex-BDR  <----------------------   New DR/BDR 
send hello

Why not just process the neighbor change event before sending the 
immediate reply?
In other words, perform the new DR/BDR election before the immediate 
reply hello?
                   
Thanks,
Acee