Subject: [nemo] questions about multihoming.

From: Wanrong Yu <[email-masked]>
Date: Wed, 11 Jun 2003 16:20:35 +0800 (HKT)

Hi,all

If there are 2 root-MRs in the same NEMO, and they have 
same prefix/length but different CoA, 
if they share the same HA, 
then how would be the routing tablez(one prefix has two 
out interfaces ) and Bindng Cache(one prefix needs two 
CoAs) of the HA?

if they have their respective HA ,
both HAs will have the chance to deal with the pakage 
destined to the NEMO, how to choose the two HAs and 
does it possible that both of the two HAs routing the 
packag to MR respectively?

Thanks a lot!

Wanrong Yu

 Wanrong Yu

---

From: Chan-Wah Ng <[email-masked]>
Date: 11 Jun 2003 16:50:43 +0800

Hello, Wanrong, 
See my responses in-line.
/rgds
/cwng

> out interfaces ) and Bindng Cache(one prefix needs two 

For the routing table, it will behave as though a normal router's
routing table having two route entries to the same destination prefix. 
AFAIK, it is perfectly valid (eg. load balancing between two routes) and
nothing NEMO specific.

Now, for the binding cache.  Having a prefix field in the binding cache
is NEMO specific, and it depends on which is the primary field (or
sometimes known as the index field) in a binding cache.  I would think
it is the home-address, and not the prefix.  Then there will be no
problem as far as I can see right now.

> packag to MR respectively?

If the packet is sent by a node outside the administrative domain of
both HA, the packet will reach one (and only one) HA depending on the
routing decision of the core/border routers.

If the packet is sent by a node behind one of the HA, the packet will be
intercepted by that HA, and tunneled to the mobile network.

No, AFAIK, you cannot have one packet reaching two separate HAs
simultaneously.  However, I do agree that there is the slight
possibility of packets from the same session (eg TCP session) going
through both HAs, eg first packet through HA1, 2nd packet through HA2,
etc.  Is this a problem?  Will it affect TCP's estimation of RTT and
parameters of the congestion algorithm, etc?

/rgds
/cwng

---

From: Chan-Wah Ng <[email-masked]>
Date: 11 Jun 2003 16:50:43 +0800

Hello, Wanrong, 

/rgds
/cwng

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 11 Jun 2003 11:35:49 +0200

Hello Wanrong.

Wanrong Yu wrote:
> If there are 2 root-MRs in the same NEMO, and they have same 
> prefix/length but different CoA, if they share the same HA, then how
>  would be the routing tablez(one prefix has two out interfaces ) and
>  Bindng Cache(one prefix needs two CoAs) of the HA?

Let me first understand your question, by drawing a picture of the
mobile network at home:

                                                                 CN
                                                     ----------/
                                         -------    |          |
    ------------------------------------| HA/BR |---| Internet |
        |                 |              -------    |          |
        |HoA1             |HoA2                      ----------
      -----    -----    -----
     | MR1 |  |LFN1 |  | MR2 |
      -----    -----    -----
        |        |        |
       --------------------
            prefix1/len1

If my picture corresponds to your model of the "multi-homed" mobile
network at home then that's fine.

At home, the HA/BR (Border Router) will have the following two entries
in its routing table:

prefix1/len1       HoA1      eth1
prefix1/len1       HoA2      eth1

Now, I consider the mobile network moves and the root-MR's attach to two
AR's respectively, as in the figure below:

                                  ----
                               --| AR |---------------------
                              /   ----                     |
                             /                             |
                  ----------/                              |
      -------    |          |                              |
  ---| HA/BR |---| Internet |                              |
      -------    |          |                              |
                  ----------\                              |
                             \                             |
                              \   ----                     |
                               --| AR |---                 |
                                  ----   |                 |
                                         |CoA1             |CoA2
                                       -----    -----    -----
                                      | MR1 |  |LFN1 |  | MR2 |
                                       -----    -----    -----
                                         |        |        |
                                        --------------------
                                             prefix1/len1

At home, the HA/BR will have the same two entries in the routing table:

prefix1/len1       HoA1      eth1
prefix1/len1       HoA2      eth1

Depending on the protocol, the following two entries might also exist in
the HA routing table, pointing to virtual tunnel interfaces tn0 and tn1.

prefix1/len1       ::      tn0
prefix1/len1       ::      tn1

The Binding Cache entries in the HA are the following:

HoA1       CoA1
HoA2       CoA2

> if they have their respective HA

The sketches are similar, and the entries in the tables are similar.

> both HAs will have the chance to deal with the pakage destined to the
>  NEMO, how to choose the two HAs and does it possible that both of 
> the two HAs routing the packag to MR respectively?

A-ha, that's a good question.  In order to find an answer, please allow
me to get back to the first figure I sketched at the beginning of this
email.  Assume that, when the "multi-homed" mobile network is at home,
that CN needs to talk to LFN.  It will send a packet to LFN, and BR will
need to forward it to either MR1 or MR2.  Which one?  I say to the first
entry in the routing table, that is to HoA1 of MR1.

Assume now that LFN wants to reply to CN.  LFN will need a default
route.  LFN receives two RA's with the same prefix1/len1: one from MR1,
the other from MR2.  Only one of those RA's can advertise as a default
route.  Which one?  I say only MR1 will advertise itself as a default
router; MR2 will not.  So, LFN will send packets to CN through MR1.

In this way, a multi-homed mobile network that is at home allows LFN and
CN to communicate ok [*].

When the multi-homed mobile network is away from home, the same
preference for MR1 will be used to get through the respective CoA's and
tunnel interfaces.

Alex
GBU

[*]Remark it uses a certain preference for MR1, which is a preference.
Other preference schemes might exist, like for example: use the entry
whose router is up, and don't use the router that is down; or use the
entry whose router's wireless is cheaper and don't use the entry whose
router's wireless is expensive.  I think that this choice of preference
should be left open.

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 11 Jun 2003 11:35:49 +0200

Hello Wanrong.

                                                                 CN
                                                     ----------/
                                         -------    |          |

prefix1/len1       HoA1      eth1
prefix1/len1       HoA2      eth1

                                  ----

prefix1/len1       HoA1      eth1
prefix1/len1       HoA2      eth1

prefix1/len1       ::      tn0
prefix1/len1       ::      tn1

HoA1       CoA1
HoA2       CoA2

Alex
GBU