Re: [OSPF] OSPFv3: Multiple Interfacee to Single Link .

Hi Keshava,

Since the Hello packets sent by R1 and R2 will have different 
router IDs there should be no confusion in this case.

This isn't explicitly mentioned in section 4.9 of 5340. Perhaps 
because it was considered too obvious?

Regards,
Paul

Keshava.Ayanur wrote:
> Hi,
> 
> Consider the following scenario.
> 
>     E0  |N1
>   R1----|				
> 	  | E1   E2  |N2
> 	  |---R2-----|
> 
> R1 E0: Link Local Address = X, Interface-Id = a.
> R2 E1: Link Local Address = Y, Interface-Id = b.
> R2 E2: Link Local Address = X, Interface-Id = a.
> 
> According to [OSPFv3], if R2 Receives Hello from R1,
> 
> Check if one of the router's link-local addresses as the source address and
> Interface ID other than the Interface ID of the receiving interface.
> 
> So we find interface R2 E2.BUT, the hello packet received was not sent by R2
> on E2.
> 
> How to handle this issue?
> 
> Regards,
> Keshava.
> 	   	  	
> 
> 
> -----Original Message-----
> From: Michael Barnes [mailto:mjbarnes@cisco.com] 
> Sent: Friday, July 10, 2009 3:55 AM
> To: Keshava.Ayanur
> Cc: ospf@ietf.org
> Subject: Re: [OSPF] OSPFv3: Multiple Interfacee to Single Link .
> 
> Hello keshava,
> 
> Keshava.Ayanur wrote:
>> Under the Section 3.9 in OSPFv3 RFC 5340
>>
>> "Each of the multiple interfaces are assigned different Interface
>> IDs.  A router will automatically detect that multiple interfaces
>> are attached to the same link when a Hello packet is received with
>> one of the router's link-local addresses as the source address and
>> an Interface ID other than the Interface ID of the receiving interface."
>>
>> If the 'Link Local address' is same for different interfaces with in the
> same Router, then how to detect that the multiple interfaces are attached to
> same link ?
> 
> That doesn't change the fact that the packet is received with one of the 
> router's own link-local addresses as the source address. This text 
> doesn't say that the source address must be different than the one for 
> the interface on which it is received. The differentiator is the 
> Interface ID, which must be unique even if the source address is not.
> 
> However, IMHO there is little advantage to having multiple interfaces to 
> a link unless the interfaces have different link-local addresses. If the 
> automatically generated link-local addresses happen to be the same, the 
> user must manually configure unique addresses on those interfaces which 
> will be connected to the same link. Otherwise any packet sent to the 
> router will be received on all of the interfaces, which seems highly 
> undesirable.
> 
> Regards,
> Michael
> 
>> Regards,
>> keshava
> 
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