Subject: [Manet-dt] Comments for the SMFdraft 01

From: Maoyu Wang <[email-masked]>
Date: Wed, 02 Nov 2005 15:18:38 -0500

Hello, Joe and Brain,

After the implementation of SMF and some tests in a MANET, we are 
considering about adding the border gateway functionality to SMF. I have 
some initial considerations about the SMF Multicast Border Gateway and 
like to use it as the first stone to rise more discussions and opinions 
about the SMF Gateway.  This time, I cannot attend the IETF meeting in 
Vancouver since it conflicts with a conference.  Wish Joe gets well 
sooner.  Wish everyone have a good time in Vancouver.

Following is the considerations:

6.  SMF Multicast Border Gateway Considerations

6.1  Forwarded Multicast Groups

Determining which groups should be forwarded to or from a MANET SMF area 
presents challenges.  Ideally, only groups for which there is active 
group membership should be injected into the SMF domain.  This might be 
accomplished by providing an IPv4 Internet Group Membership  Protocol 
(IGMP) or IPV6 Multicast Listener Discovery (MLD) proxy function so that 
MANET SMF nodes can inform attached gateways (and hence multicast 
networks) of their current group membership status.

Consideration:
Propagating IGMP or MLD in MANET means propagating packets with Link 
Local address in MANET? Is that appropriate? Instead of that, Should we 
define some SMF control message to propagate the membership status? How 
is everyone' opinion?  

6.2  Multicast Group Scoping

  (TBD)
Consideration:
 My suggestion for IPv6: Any packet with destination starting with 
ff05::/32 is restricted in MANET. Packets with destination starting with 
ff0e::/32 are forwarded to outside of the MANET before any new address 
scopes are defined.

6.3  Duplicate Packet Detection Marking

Packets sourced external to an SMF area may not have duplicate packet 
sequencing properly applied and the gateway may need to provide that 
sequencing information upon entry to the network.  In the case of IPv6, 
the gateway can apply the SMF DPD Hop-by-Hop options header to packets 
forwarded into the MANET area for those packets that do not already have 
the option applied.  This header option provides the side benefit that 
the gateway can explicitly determine if the packet has already been 
marked and can use the packet identification field to determine that it 
is not re-injecting a duplicate packet. <>

Consideration:
 A gateway marks an external sourced multicast packet based on its 
<sourceAddress::destinationAddress>. Each 
<sourceAddress::destinationAddress> uses a sequence number space 
increasing from 0. There is a lifetime after a sequence number space is 
used last time. After the lifetime is expired, the sequence number space 
for the source address should increase from 0 again. The strategy will 
benefit multiple gateways. Keep multiple gateways add the sequence 
number at the same starting number. Details are in next " 6.5 multiple 
gateways" part.  <> 

 For IPv4, it is RECOMMENDED that gateway nodes re-sequence the ID field 
of packets injected into the area.  However, the IPv4 ID field does not 
provide the gateway with explicit information on whether the field has 
been previously set for SMF purposes.  Thus, in cases where the 
potential exists that duplicate packets may be re-injected by a gateway 
into an SMF area, it may be desirable to use a more explicit marking 
such as the alternative IPv4 DPD header option described in Section 4.1.1. 

 _(If multiple gateways are injecting packets, how do we make sure  that 
dups are sequenced the same way? )_

 Please see "multiple gateways" for the suggestion.

6.4  Interface with Exterior Multicast Routing Protocols

   (TBD)

6.5 Multiple Gateways

Consideration:

When multicast packet enters the MANET from outside, we don't need 
multiple gateways injecting the same multicast packet. The main strategy 
should be how to keep a gateway injects the multicast packets instead of 
all gateways injecting the same multicast packet.

There is a gateway flag in each duplicate entry indicating that if this 
entry is originally generated by this gateway or by other nodes. When it 
is the first time to receive a packet from this external source with the 
<sourceAddress::destinationAddress>, before labeling any ingressing 
packets, a gateway checks if there is a duplicate entry for the 
<sourceAddress::destinationAddress>  and if its gateway flag indicates 
that this entry represents a duplicate packet not originally marking by 
this gateway. If yes, the multicast packet already enters MANET through 
other gateway, the gateway would not bother to mark the ingressing 
packet from this source address and has the 
<sourceAddress::destinationAddress>. Otherwise, labeling the ingressing 
packet with a sequence number start from 0.  If two gateways almost 
receive the same multicast packet from the same external source, they 
will mark the same packet by the same sequence number. The DPD works 
fine.  Sooner or later, if one gateway finds a external sourced packet 
has a entry in the duplicate table and its sequence number is bigger 
than current its own sequence number for the same external sourced node, 
it will stop marking multicast packet from the same source addresses. 
However, the gateway should keep update the lifetime for the  
<sourceAddress::destinationAddress> every time when it inserts an entry 
with <sourceAddress::destinationAddress> in its duplicate table because 
receiving a copy from other gateway. After the lifetime for 
<sourceAddress::destinationAddress> is expired, the 
<sourceAddress::destinationAddress> will be removed. Sequence number 
will start from 0 again. Otherwise, if the lifetime for 
<sourceAddress::destinationAddress> is not expired, this gateway does 
not mark any ingressing packets with the 
<sourceAddress::destinationAddress>.

When packets enter outside network from MANET, how can we keep only a 
gateway removes the DPD part used in MANET and sends the multicast 
packet out instead of multiple copies of the same packet are sent from 
multiple gateways? Before a gateway remove the DPD part, checking if a 
multicast packet with the same <sourceAddress::destinationAddress> has 
been received from outside network? If yes, other gateway already take 
care of the group of multicast packets, this gateway doesn't need to 
forward the packet with the same <sourceAddress::destinationAddress>. 
Otherwise, the gateway removes the DPD part, and forwards it to outside 
network. If two gateways almost remove the DPD parts at the same time 
and forwarding the multicast packet into outside network, sooner or 
later, they will notice that. However, there is no way to decide who 
should stop.  Without extra control message exchanges between the 
gateway, there is no way to stop multiple copies of the same packet 
injecting to outside network because there is no DPD at the routing 
layer for other multicast routing protocol.

Maoyu

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