Subject: Re: Re: [OSPF] OSPFv3 Draft 9: Equal-cost paths through mutliple interfaces in a single link

From: "Vivek Dubey" <[email-masked]>
Date: 16 Jun 2006 05:38:23 -0000

Hi,  
There are a few reasons for the newly active interface to reform adjacencies. First is that it is unknown why the standby interface is no longer able to see the hello packets from the active. It is possible, for example, that the standby has been physically rewired such that it is connected to a different LAN, or a VLAN may have been reconfigured, and there are many other possibilities.

<vivek> Reason is unknown no doubt when Active's hellos are not seen.
But to quote draft "This failure can be detected by the router itself, when the other interfaces to the same link cease to hear the router's own Hellos or through internal mechanisms such as when the interface is disabled by a configuration change"
So in case of internal mechanisms "reasons can be known".

On top of that, is that the standby has a different interface ID and also a different link-local address. It must be assured that the neighbors have the correct information. If the adjacencies are not reformed, then it is possible that the neighbors will keep out of date information in their neighbor data structure and/or LSAs.

<vivek> Re-origination of LSAs should be able to take care of this scenarion. Section 3.4.3 of Draft 10 has few events which can play a role.

-Vivek

On Thu, 15 Jun 2006 Michael J Barnes wrote :
>Hello Ramana,
>
>There are a few reasons for the newly active interface to reform adjacencies. First is that it is unknown why the standby interface is no longer able to see the hello packets from the active. It is possible, for example, that the standby has been physically rewired such that it is connected to a different LAN, or a VLAN may have been reconfigured, and there are many other possibilities. On top of that, is that the standby has a different interface ID and also a different link-local address. It must be assured that the neighbors have the correct information. If the adjacencies are not reformed, then it is possible that the neighbors will keep out of date information in their neighbor data structure and/or LSAs.
>
>Thanks,
>Michael
>
>Ramana Koppula-G20085 wrote:
>>Hi,
>>  In Section 3.9: "The interfaces in this list are used as equal-cost paths when routes are installed in the routing table."
>>  In the same Section: "If the Active Interface fails, another will have to take over, reforming all neighbor adjacencies from scratch."
>>  The motive of equal-cost paths is to retain a route to a router even if one path goes down.
>>By mandating the StandBy to reform all the neighbor adjacencies from scratch, are we not losing that edge.
>>  thanx
>>ramana
>>
>>
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