Subject: Re: [netext] Questions on: draft-ietf-netext-logical-interface-support-05.txt

From: <[email-masked]>
Date: Tue, 1 May 2012 14:30:02 +0000

On 4/30/12 10:45 PM, "ext Sri Gundavelli" <[email-masked]> wrote:

>
>>> 
>>> 
>>>> 2. Regarding path MTU, the I-D says that in the case where the MN is
>>>> attached simultaneously to multiple interfaces, the LIF will choose
>>>>the
>>>> smaller of the MTU values of the physical interfaces.  However the I-D
>>>> also says that the LIF has awareness of forwarding packets on the
>>>> interface from which a packet was received. If that is the case, why
>>>> would
>>>> the LIF be configured with the lower value MTU? The LIF should be able
>>>> to
>>>> choose the appropriate MTU for sending a packet depending on the
>>>> interface
>>>> over which the packet is sent/received.
>>>> 
>>> 
>>> [Sri] Keeping the lower of the MTU values across different interfaces
>>> will ensure there is no MTU change notification to the ND stack after
>>> each handover. It will keep a stable MTU value.
>> 
>> But it comes at the cost of sending packets on the interface in a
>> suboptimal manner. As a result the bandwidth of the air-interface is
>>(may
>> be) wasted. Since the LI knows which of the interfaces to send the
>>packets
>> on, why does it need to adapt to the lower value MTU? I do not believe
>>it
>> is necessary.
>
>The other aspect is constant MTU change at each handoff. So, we can leave
>both the considerations and let implementations decide.

Change of the underlying interface has an impact on MTU as well as
latency, congestion etc. Hence just maintaining a constant MTU is not
sufficient. It would be preferable to allow for the LIF to use the Max MTU
value of the underlying physical interface. I am okay with your suggestion
to document both approaches.

>
>
>
>
>>> 
>>> 
>>>> 3. The statement: "The logical interface adapts to the point-to-point
>>>> link
>>>> model." is not completely clear. What exactly is the LIF adapting to?
>>>> 
>>> 
>>> [Sri] We have had this discussion in the past on this topic. LIF is
>>> adapting to P2P link model. May be we can add more details.
>> 
>> I am still at a loss to understand what you mean when you say "LIF is
>> adapting to P2P link model". What exactly is happening at the LIF in
>>terms
>> of behavior?
>> 
>
>Every interface that is exposed to the ND stack is reflecting the
>interface type, shared/p2p. There is even a socket API to get this
>property and its used by the application/ND stack for different purposes,
>Now, the question is about LIF, what is the tag that exposed to the upper
>layer. The LIF operation has no bearing on the type and given that we
>have pre-established assumption on the link model, we rather expect the
>LIF be of another P2P link type. That's all to it.

Would be good to explain this in the I-D.
If the underlying physical interface is not of type P2P does the LIF then
create such a link type between the MN and the AR/MAG?
The LIF is yet another interface that is available on the MN. Any
application may potentially use it. Is the intent that the LIF is used
only in a PMIP6 domain? How does the MN know when the LIF interface is to
be used Vs any of the other interfaces?

-Raj

>Sri

---

From: Sri Gundavelli <[email-masked]>
Date: Tue, 1 May 2012 08:02:25 -0700

> to document both approaches.

Ack

> create such a link type between the MN and the AR/MAG?

Sure

> be used Vs any of the other interfaces?

This is touching Pete's comment. We will respond to this.

Regards
Sri