Subject: Re: [manet] The Problem of Alien Node

From: "Yasser A. Lotfy" <[email-masked]>
Date: Mon, 01 Sep 2003 11:24:52 -0400

Hi,
That is exactly my point. Ad-hoc nodes may not always have a MANET_PREFIX IP address due to possibilities of nodes roaming with a static IP, and the chances of ad-hoc network getting partitioned or merged.

Therefore, it is not possible for ad-hoc nodes to rely merely on MANET_PREFIX IP address to distinguish local nodes (LAA). The gateway also will asume nodes that don't have MANET_PREFIX IP address are external, and will forward packets outside the ad-hoc. While in fact some nodes that don't have MANET_PREFIX IP address are local nodes, with global static IP (I call it alien nodes).

Therefore, I believe, there should be a registration mechanism for all alien nodes at the gateway.

Any comments? any reason why not?

yasser
----------------------------------------------
I'm sorry but the point that you are trying to get across is not very 
clear, and your terminology is quite confusing...
perhaps it would become clearer if we knew what your references 
were...[047-01] and [048-01].

when building a scenario that incorportes both terrestrial and ad hoc nodes, it is best to use address in MANET_PREFIX to identify ad hoc nodes.  this way the gateway knows which address are in manet and which are in terrestrial network.  These address spaces should be mutually exclusive, or you are going to run into the problems that you describe(atleast thats what I think you are talking about).

alternately, if you decide that the two address spaces can intermingle, then you need to run complex registration/deregistration protocols at the gateway to inform the gateway which addresses(nodes) are in the manet.(some hybrid form of MIP).

-manish

Yasser A. Lotfy wrote:
> Hi,
> 
> I hope you read the attached (word) document which raises awareness of the 

> problem of alien node. Sorry I have to make it in MS-Word since some of the symbols

> can not be done as text.
> 
> The problem is simply due to the confusion that takes place when gateways announce

> there ability to forward packets to generic addresses. Some local ad-hoc nodes may fall

> in this generic address range. Therefore, packets may (incorrectly) be forwarded to GW.

> I hope to get feedback if any solution currently exist to this problem. 
> 
> yasser
> ---
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---

From: "HyunWook Cha" <[email-masked]>
Date: Wed, 3 Sep 2003 09:54:43 +0900

Hi Yasser,
I think "registration" is necessary for communications which are not
only manet local but also across Internet.
I mentioned this point at my previous posting.
But I think the "registration" can not be an solution for the "Alien
Node Problem".
Please think about this case. There are multiple gateways and a manet.
Manet nodes may have different sets of gateways because of partitions. 
And, if a gateway chosen by souce node does not belong to the gateway
set of destination node, it will forward packets destined to desination
toward Internet.
I think a global static ip which you are considering is not globally
routable(reachable) since a manet node with globally routable global ip
is also reachable across Internet althogh it is local manet node.
If so, evenually souce node will be notified by ICMP destination
unreachable and do route discovery again in case of reactive protocols.
I think this is enough for destination node with the "global static ip"
which is not globally routable.

Regards,

++++++++++++++++++++++++++++++++++++++++++++++++++++

HyunWook Cha

Researcher  
NGI Standards Research Team
Protocol Engineering Center, ETRI
161 Kajong-Dong, Yusong-Gu, Taejon, 305-350, KOREA
(Tel) +82-42-860-1076

++++++++++++++++++++++++++++++++++++++++++++++++++++

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Yasser A. Lotfy
> Sent: Tuesday, September 02, 2003 12:25 AM
> To: [email-masked]; Manish Karir
> Subject: Re: [manet] The Problem of Alien Node
> 
> 
> 
> Hi,
> That is exactly my point. Ad-hoc nodes may not always have a 
> MANET_PREFIX IP address due to possibilities of nodes roaming 
> with a static IP, and the chances of ad-hoc network getting 
> partitioned or merged.
> 
> Therefore, it is not possible for ad-hoc nodes to rely merely 
> on MANET_PREFIX IP address to distinguish local nodes (LAA). 
> The gateway also will asume nodes that don't have 
> MANET_PREFIX IP address are external, and will forward 
> packets outside the ad-hoc. While in fact some nodes that 
> don't have MANET_PREFIX IP address are local nodes, with 
> global static IP (I call it alien nodes).
> 
> Therefore, I believe, there should be a registration 
> mechanism for all alien nodes at the gateway.
> 
> when building a scenario that incorportes both terrestrial 
> and ad hoc nodes, it is best to use address in MANET_PREFIX 
> to identify ad hoc nodes.  this way the gateway knows which 
> address are in manet and which are in terrestrial network.  
> These address spaces should be mutually exclusive, or you are 
> going to run into the problems that you describe(atleast 
> thats what I think you are talking about).
> 
> alternately, if you decide that the two address spaces can 
> intermingle, then you need to run complex 
> registration/deregistration protocols at the gateway to 
> inform the gateway which addresses(nodes) are in the 
> manet.(some hybrid form of MIP).
> 
> -manish
> 
> 
> 
> Yasser A. Lotfy wrote:
> > Hi,
> > 
> > I hope you read the attached (word) document which raises 
> awareness of 
> > the
> 
> > problem of alien node. Sorry I have to make it in MS-Word 
> since some 
> > of the symbols
> 
> > can not be done as text.
> > 
> > in this generic address range. Therefore, packets may 
> (incorrectly) be 
> > forwarded to GW.
> 
> Get advanced SPAM filtering on Webmail or POP Mail ... Get 
> Lycos Mail! http://login.mail.lycos.com/r/referral?aid=27005
>

---

From: Manish Karir <[email-masked]>
Date: Wed, 03 Sep 2003 11:12:28 -0400

routing protocols in the two domains(ad hoc and terrestrial) play very 
different roles, terrestrial routing protocols(most) are generally 
proactive in nature, and they spread information regarding the 
availability of a "subnet" to the rest of the world.  ad hoc routing 
protocols(lets just focus on AODV  for now) are on-demand and they 
convey the reachability of "individual" nodes.  Now when you try to 
build gateways, you have to be careful in how you translate these two 
very different semantics.

first thing you want to consider is that you dont want the mobility of 
nodes in the manet to be propagated to the Internet, this lead us to the 
approach were you try to represent the entire manet subnet as a single 
prefix.  This approach also makes entities like the IANA happy, as the 
"manet provider" is the responsible party for this manet subnet, and 
they dont have to hand out 5million IP's to individual manet nodes.

now this approach work fine as long as you have a single gateway.  The 
real problem is when we allow for multiple gateways.  In this case you 
end up with all kinds of problems due to the different between the 
nature of the two protocols.  For example, you can end up with 
inefficient routing paths, as hop count information from within the ad 
hoc network is not propagated to the terrestrial routing protocol.  You 
can also end up with unreachable nodes, as partitioning in the ad hoc 
network, can create scenarios where some gateways can only reach some 
nodes and not the entire manet prefix.

there are a few possible directions one can take to try to fix this problem:

- dont do it: dont allow for multiple gateways, most subnets ususually 
have only a single point of attachment to the higher network, and since 
allowing for multiple gateways is a prickly problem, why bother, and 
complexity only adds more ways in which the system can fail 
anyways...etc. etc.

- make up a complex protocol: this approach tries to basically undo the 
effects of the on-demand protocol being run in the manet, you propagate 
hop count information, to the gateway nodes, you propagate which nodes 
are present/reachable by the gateway for each node(registeration), etc.
one possible candidate for this has been the use of mobile IP(there are 
various references on this approach)

- run a proactive routing protocol: this approach would probably work a 
little bit better than making up a new protocol, but there are still a 
lot of corner cases to consider, and the jury is still out on whether 
proactive protocols are a good solution for ad hoc networks(please lets 
not start another thread on this argument and get distracted).

bottom line: yes multiple gateways create a problem, and no there is no 
easy solution, the only point I think I'm trying to get across is that 
"alien node problem" is a problem only under certain assumptions of what 
you are allowing in the network(s). It is not a general problem with 
acheiving interoperability between ad hoc and terrestrial routing protocols.

we currently have a paper under submission regarding some of these 
issues, but I hesitate to post non peer reviewed work to the list(who 
knows the work might be completely wrong in assumptions and approach)

-manish karir

PS: dont forget the problem of multicast routing and building a gateway 
to support that.

---

From: "HyunWook Cha" <[email-masked]>
Date: Thu, 4 Sep 2003 10:57:45 +0900

HI Manish,
Please see inline comments.

> Behalf Of Manish Karir
> Sent: Thursday, September 04, 2003 12:12 AM
> Cc: [email-masked]
> routing protocols in the two domains(ad hoc and terrestrial) 
> play very different roles, terrestrial routing protocols(most) are
generally 
> first thing you want to consider is that you dont want the 
> mobility of nodes in the manet to be propagated to the Internet, this 
> lead us to the approach were you try to represent the entire manet
subnet as 
> a single prefix.  This approach also makes entities like the IANA 
> happy, as the "manet provider" is the responsible party for this manet
subnet, and 
> they dont have to hand out 5million IP's to individual manet nodes.

Right. In Mobile IP, only HA has knowledge of current attach points of
its cared MNs.

> now this approach work fine as long as you have a single 
> gateway.  The real problem is when we allow for multiple gateways.  In
this 
> case you end up with all kinds of problems due to the different
between the 
> inefficient routing paths, as hop count information from 
> within the ad hoc network is not propagated to the terrestrial routing

> protocol.  

You know, the purpose of Internet connectivity of MANET we are
considering is that manet nodes can start(initiate) communication with
locally unreachable but globally reachable nodes. To do so, a manet node
has to configure its global address with the prefix of a gateway or
gateways known to it in the stateful or stateless manner.
And the manet node uses newly configured global ip as source address
when it initiates communication with peer node.
Since general MANET node is not equipped with MIPv6, it cannot perform
procedure like RR in MIPv6.
So, peer node can see only global ip used as source address by the manet
node when the communication is started. 
Althogh the manet node has multiple globla IPs from multiple gateways
and gateways which do not have same prefix as the ip used for 
the communication has route entry or some registration information for
the ip, 
inbound traffic always arrives the gateway with the same prefix as ip
which is chosen as source ip by the manet node.
If so, what makes inefficient routing paths problem under multiple
gateways?

> You can also end up with unreachable nodes, as partitioning in the ad
hoc 
> nodes and not the entire manet prefix.      

This also happens in single gateway condition because of the nature of
MANET. 
This is not specific to the multiple gateways case.

> - dont do it: dont allow for multiple gateways, most subnets 
> ususually have only a single point of attachment to the higher
network, 
> and since allowing for multiple gateways is a prickly problem, why
bother, and 
> complexity only adds more ways in which the system can fail 

See the charter of IETF Multi6 wg. I think the use of multiple gateways
can help Internet connectivity of MANET 
which has extremely dynamic topology by its nature.

> - make up a complex protocol: this approach tries to basically undo
the effects of the on-demand protocol being run in the manet, you 
> propagate hop count information, to the gateway nodes, you propagate
which nodes are present/reachable by the gateway for each 
> node(registeration), etc. one possible candidate for this has been the
use of mobile IP(there are various references on this approach)

I also think the reachability informaiton for manet node should not
propagate in proactive manner when reacive routing protocol is used.
As I mentioned above, this kind of registration does not help.
Could you point which approaches use Mobile IP? I also read a few papers
including MIP-MANET. 
I am considering registration scheme of Mobile IP can help address
unreachable manet node and developing ns2 simulation codes.
What do you think of this approach?

> not start another thread on this argument and get distracted).

Regardless of the type of routing protocol, reachability information of
another addresses of destination manet node do not help in a gateway.
 
> acheiving interoperability between ad hoc and terrestrial 

IMO, the use of multiple gateways does not generate any issue which does
not happen in the use of single gateway.
Could you tell me how all manet nodes can choose the same one gateway
when multiple gateways is available?
  
> knows the work might be completely wrong in assumptions and approach)

I am interested in your idea and hope we can handle many issues of this
area successfully.

HyunWook Cha
 
> > only manet local but also across Internet. I mentioned this 
> point at 
> > my previous posting. But I think the "registration" can not be an 
> > solution for the "Alien Node Problem".
> 
> 
> > set of destination node, it will forward packets destined to 
> > desination toward Internet.
> 
> 
> > routable(reachable) since a manet node with globally 
> routable global 
> > ip is also reachable across Internet althogh it is local manet node.
> 
> 
> > unreachable and do route discovery again in case of reactive 
> > protocols. I think this is enough for destination node with the 
> > "global static ip" which is not globally routable.
> > 
> > Regards,
> >