Subject: [mif] about draft-hui-ip-multiple-connections-ps-02

From: marcelo bagnulo braun <[email-masked]>
Date: Sun, 15 Mar 2009 20:19:09 +0100

Hi,

thanks for the draft, certainly is pointing to some relevant problems 
imho. I have some clarifying questions below...

2.1. Default Gateway

   The Windows operating system in the host follows the default gateway
   mechanism, which will choose the unify gateway among more than one
   default routes ('0.0.0.0'), the detail is described in RFC1122. The
   default gateway guarantees there always has a route to network when
   the host can not find a specific route for a datagram in the route
   table.

   But when it comes to multi-homing, the default gateway also causes
   all the flows go out through one interface, although there has more
   than one network connections.  Nowadays there are diverse networks
   can be chosen by the user, and the terminal have the capability and
   interfaces to connect to more than one networks at the same time. It
   is possible and necessary for the user to require connecting to
   different networks to ensure the best user experiences of different
   services, but the default gateway mechanism only allows one
   connection at once. Although you can connect your host to several
   networks physically, and each network has already assigned a IP
   address for your host interface, even you can see different default
   routes in the route table, all the flow goes to the default gateway
   chosen by the operation system other than different gateways actually.

I am not convinced the problem you want to point is well characterised 
in here. I mean, you seem to imply this is a routing problem, but then 
it seems (from your examples aboves) that what you really want is that a 
given application uses one interface and a different application use 
another one. This is not celar to me that it is a routing problem or 
that the IP layer is the right place to solve it.

 2.2.1. DNS consideration

   DNS will be configured to the interface manually or by DHCP procedure,
   and multiple interfaces will obtain multiple DNS. The host will
   reserve several DNS in this situation. Referring to different domain
   names the host should query proper DNS so that the domain names can
   be resolved. The problem is current DNS selection mechanism is lack
   to choose a right one for specific visited domain name, so that we
   need to merge multiple DNS to provide the host with the best
   connectivity.

This is only a problem in the case of dual faced dns, right?
Or are you considering other situations, like i dont know Web proxies 
and the like?
You may want to be more explicit abotu what is the problem you are 
aiming at, since it is easy to envision many situations where there is 
no aparent problem

         2.2.2. Metrics consideration

   Metrics are used to measure the performance of routings, the lower
   metric it owns, the higher priority it has. For example, the default
   gateway is chosen based on the metric rule as RFC1122 description,
   The one have the lowest metric value becomes to the default gateway
   among several connected gateways, and the interface correspond to
   this gateway turns to be the default interface.

I would argue that if you are connecting to two different networks, 
comparing the metric does not make much sense, i guess. I mean, i 
understnad that comparing the metric make sense when the  routes belong 
the the same network. I woudl argue that in the case of a multihomed 
device, the most importnat aspect to choose a route over a different 
route over a different provider is internal policy

       2.2.3. TOS consideration

   TOS can be a parameter of routing item to indicate which kind of IP
   data is suitable to deliver by this routing. The multiple interfaces
   will connect to multiple access networks, so that the preference of
   TOS need to be merged to have a better performance of data delivery.
   For example, the WiFi access could indicate itself has broader
   bandwidth comparing with 2G access, and set the TOS as broad
   bandwidth. When another interface connects the Ethernet, the TOS is
   also set as broad bandwidth preferred. In this situation, it needs
   some mechanism to merge and reorder the TOS getting form multiple
   interfaces.

I am not sure how widely used is this...

         2.3. Source address selection for IPv4

   For the host has more than one IP addresses which are obtained by
   multiple interfaces, the source address selection is the key issue in
   order to use multiple interfaces reasonably. The application needs to
   select right source address so that the data will be delivered by the
   corresponding interface. This mechanism is lack currently which needs
   to be solved in multiple interfaces situation.

I understnad that the current practice is that the host will use the 
source address of the outgoing interface... would this practice have any 
issue? I mean, the source address would match the outgoing network. so 
it seems to do what it is expected....

          3. Analysis of Related Work in IETF

I didn't find that section very useful actually.

        4. Requirements for Simple IP Multi-homing

   Based on problem statements and related work analysis, the
   requirements for simple IP multi-homing is concluded and listed as
   follows:

   1) The host with multiple network interfaces should be capable to
   connect with different networks simultaneously.

i agree with this one

   2) The default gateway mechanism needs to be improved to support
   several gateways working at the same time.

not sure what you mean by this....

   3) New metric mechanism must be defined to adapt to various network
   cards nowadays.

this seems more a solution than a requirement. I mean, what is the 
expect behaviour that you want to support? maybe metrics is the right 
way to go or maybe some other approach would work

   4) The policies to assign different flows to the appropriate
   interface are required, and how to apply the policies to the host
   need to be considered as well.

right, this makes sense to me

   5 Network side should be capable of distributing the IP flow
   according to some parameters, such as IP address prefix, network type
   and so on.

i don't understnad what you mean by this one, could you expand?

Regards, marcelo

---

From: Min Hui <[email-masked]>
Date: Mon, 16 Mar 2009 17:49:10 +0800

Hi, marcelo
Thanks for your comments, pls see my answers below.
- Hui Min

2009/3/16 marcelo bagnulo braun <[email-masked]>
Hi,

2.1. Default Gateway

I am not convinced the problem you want to point is well characterised
in here. I mean, you seem to imply this is a routing problem, but then
it seems (from your examples aboves) that what you really want is that
a given application uses one interface and a different application use
another one. This is not celar to me that it is a routing problem or
that the IP layer is the right place to solve it.

A: It is a routing problem, but it will affect the application to
choose a right interface, which is the key issue of mif. The reason is
the application will not appoint a source address in most situations
currently. The source address will be determined by host operating
system after querying the host routing table, if there is any
available routing item for the destination, the corresponding source
address of this routing item will be selected. In most cases, the
routing item of default gateway will be used, so that every
application will use the same interface. This problem can be solved in
IP layer, e.g. specify the source address of the application according
to the policy.

2.2.1. DNS consideration

A: The problem is when the host gets multiple IP addresses for its
multiple interfaces, it will get multiple DNS addresses as well, so
that query  which DNS to obtain the IP address of a domain name is a
question needs to be solved. It is similar with the source address
selection problem. Could you give more explanation of dual faced DNS
you mentioned?

I would argue that if you are connecting to two different networks,
comparing the metric does not make much sense, i guess. I mean, i
understnad that comparing the metric make sense when the  routes
belong the the same network. I woudl argue that in the case of a
multihomed device, the most importnat aspect to choose a route over a
different route over a different provider is internal policy

A: I agree with you that comparing the metric of two different
networks is meaningless. However, the current operating system really
does this to choose routing among several different networks. For
example, current metric rules define the 100M bps Ethernet network
card to be 20 and 10M bps to be 30, but the CDMA data card set its
metric value as 1, although its speed is lower than 100M bps Ethernet
network card, and the host will choose the CDMA data card as the
default network card. Internal policy is needed to adjust and modify
the metrics of different networks to work coherently, and it is what
the metrics consideration section wants to indicate.

     2.2.3. TOS consideration

A: As depicted in RFC1122, TOS is a necessary parameter to choose a
suitable routing. And different applications have different
requirements of access network, which can be reflected as TOS. So we
think TOS will be useful in multiple interface situations.

I understnad that the current practice is that the host will use the
source address of the outgoing interface... would this practice have
any issue? I mean, the source address would match the outgoing
network. so it seems to do what it is expected....

A: There is no problem that the source address would match the
outgoing network, the problem is how to select the right source
address for a specific application so as to deliver the data by the
right access network.

A: Thanks for your doubt, we will think over it.

i agree with this one

A: The meaning is the default gateway mechanism only support one
outgoing interface at once, we need to improve it to support multiple
interface simultaneously. The detail description of default gateway
problem can be seen in section 2.1.

A: You are right, we will modify this bullet in the next version.

A: That is the policy in the network side. Corresponding to the policy
of sending data mentioned in the fourth bullet, the policy of
receiving data is also needed, which can be apply in the network side.
The network can determine forward a specific IP flow to which
interface of the destination host according to the policy.

Regards, marcelo

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---

From: marcelo bagnulo braun <[email-masked]>
Date: Mon, 16 Mar 2009 18:13:29 +0100

> IP layer, e.g. specify the source address of the application according

First of all, if i understand this correctly, what you want is that 
certain applications use a given interface and other applications use a 
different one, right?

On one hand, i see your point with this being related to routing cause 
if we have normal routing tbale,s we will use only one default route 
irresepctively of the application. so, in order to deal with this we 
need change that. I agree so far

On the other hand, you seem to want to use the source address as a mean 
for the application to select the interface. I mean, if the application 
makes a bind to a given source address, and we are in the strong host 
model, that it will need to use the associated interface. This could 
work, but i think this is solution space. I mean, you could think of a 
different mechanism to bind a given app to an interface and then simply 
select the source address as it is currently done

So, i think for a problem statement to be in good shape, you need to 
distinguish which are the problems and what is the solution
> selection problem. Could you give more explanation of dual faced DNS

becuase this is only a problem if the DNS reply is different depending 
on the DNS server you use, right? I mean, if all the DNS servers in the 
different interfaces provide the same reply, then it is irrelevant which 
one do you choose, right?
So, DNS servers provide different replies in multiple situations. But i 
think the most critical one is dual faced dns, in which the reply may 
simply not be valid if a differnet interface is used or you may be able 
to resolve a given query if the wrong dns server is used.
> the metrics consideration section wants to indicate.
right, see your point. Again, harmonizing the metrics is one possible 
solution. You probably want to describe the problem and leave open how 
this can be solved

> think TOS will be useful in multiple interface situations.

right, my question was how widely used is this. I mean how much of the 
internet traffic actually sets the TOS?

> address for a specific application so as to deliver the data by the

right, as we disucssed above, this seems to be more a result of a 
particular solution rather than a problem in itself

> problem can be seen in section 2.1.
right, i see what you mean now and i agree this is a problem

> interface of the destination host according to the policy.

right, i see what you mean. I am not sure which element of the network 
would do that... i mean, are you assuming that all interfaces are being 
connected to the same ISP? If not, i am not sure how would you do this...

---

From: Min Hui <[email-masked]>
Date: Tue, 17 Mar 2009 17:31:23 +0800

Hi, marcelo

pls see my reply in line.

thanks.

- Hui Min

2009/3/17 marcelo bagnulo braun <[email-masked]>:
> First of all, if i understand this correctly, what you want is that certain
> applications use a given interface and other applications use a different
> one, right?

You're right, it's the aim.
>
> On one hand, i see your point with this being related to routing cause if we
> have normal routing tbale,s we will use only one default route
> irresepctively of the application. so, in order to deal with this we need
> change that. I agree so far
>
> On the other hand, you seem to want to use the source address as a mean for
> the application to select the interface. I mean, if the application makes a
> bind to a given source address, and we are in the strong host model, that it
> will need to use the associated interface. This could work, but i think this
> is solution space. I mean, you could think of a different mechanism to bind
> a given app to an interface and then simply select the source address as it
> is currently done
>

ok, thanks.

> becuase this is only a problem if the DNS reply is different depending on
> the DNS server you use, right? I mean, if all the DNS servers in the
> different interfaces provide the same reply, then it is irrelevant which one
> do you choose, right?
> think the most critical one is dual faced dns, in which the reply may simply
> not be valid if a differnet interface is used or you may be able to resolve
> a given query if the wrong dns server is used.

I understand your meaning, It is indeed a problem when each DNS server
provides different replies.

> solution. You probably want to describe the problem and leave open how this
> can be solved
>
>
>>     2.2.3. TOS consideration
>>

The 3G network use TOS as one of the QoS parameters, and we suppose to
use it in the multiple interfaces situation.

> right, as we disucssed above, this seems to be more a result of a particular
> solution rather than a problem in itself

> right, i see what you mean. I am not sure which element of the network would
> do that... i mean, are you assuming that all interfaces are being connected
> to the same ISP? If not, i am not sure how would you do this...

In technical perspective,  the element would be the gateway which in
charge of all the interfaces, e.g. PDN GW in 3GPP architecture, LMA in
PMIP domain; In deployment perspective, it's better when all
interfaces connect to the same ISP, the negotiation is needed when
multiple ISP are involved.

---

From: marcelo bagnulo braun <[email-masked]>
Date: Thu, 19 Mar 2009 10:12:40 +0100

> use it in the multiple interfaces situation.
ok, but does any other network uses this?
I mean, if only 3g networks use this, this is only a problem when 
simultaneously connecting to multiple 3G networks, so i am not sure how 
common this is

....
> multiple ISP are involved.

but it is not the network who can decide the IP address to use to 
forward packets....

I mean, suppose that you have a node A in the internet that wants to 
send a flow to a mif device.
Let's suppose that the MIF device has different IP addresses per interface
Now, the selection of the interface is perfromed by node A when it 
selects the destiantion address it will send the flow to. I  fail to see 
how the netwokr would be able to send packet to a different address 
(wihtout using MIP, of course)

What is your view on this?

Regards, marcelo

---

From: Min Hui <[email-masked]>
Date: Fri, 20 Mar 2009 16:47:24 +0800

Hi,

pls see inline reply. thx.

> simultaneously connecting to multiple 3G networks, so i am not sure how
There are 3GPP and 3GPP2 mobile network which have been deployed, both
of them support it.
Some network use it for Wifi access network as well.
There are more and more motivation to do different service quality
categorization,
such as put the p2p more low level.

>>> would
> but it is not the network who can decide the IP address to use to forward
> packets....
>
> I mean, suppose that you have a node A in the internet that wants to send a
> flow to a mif device.
> Now, the selection of the interface is perfromed by node A when it selects
> the destiantion address it will send the flow to. I  fail to see how the
> netwokr would be able to send packet to a different address (wihtout using
> MIP, of course)

I agree with you, if we don't consider MIP and PMIP, the requirement
of network side policy is not essential.

---

From: marcelo bagnulo braun <[email-masked]>
Date: Fri, 20 Mar 2009 16:19:51 +0100

> of network side policy is not essential.

i understand that mobility related topics are out fo the scope of this 
effort, right?

Regards, marcelo

---

From: Behcet Sarikaya <[email-masked]>
Date: Fri, 20 Mar 2009 13:46:08 -0700 (PDT)

Hi Min,
  Pls see inline, thx.

Behcet

________________________________
From: Min Hui <[email-masked]>
To: marcelo bagnulo braun <[email-masked]>
Cc: mif <[email-masked]>
Sent: Friday, March 20, 2009 3:47:24 AM
Subject: Re: [mif] about draft-hui-ip-multiple-connections-ps-02

Hi,

[behcet] I believe you. I think it would be more convincing if you could give us which standard, e.g. 23.401 this is mentioned. Without any evidence we just need to believe you.

---

From: Min Hui <[email-masked]>
Date: Mon, 23 Mar 2009 09:30:06 +0800

Hi, Behcet

Pls see my reply below, thx.

2009/3/21, Behcet Sarikaya <[email-masked]>:
> [behcet] I believe you. I think it would be more convincing if you could
> give us which standard, e.g. 23.401 this is mentioned. Without any evidence
> we just need to believe you..
>
3GPP standard 24.008 can be refered to, thx.