Re: [magma] Question about proxy implemenation in RFC 4605

"Alvaro Fernandez" <Alvaro@soportemv.com> Tue, 02 November 2010 08:39 UTC

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Thread-Topic: [magma] Question about proxy implemenation in RFC 4605
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From: "Alvaro Fernandez" <Alvaro@soportemv.com>
To: "Kunal Shah" <kunal.shah@ericsson.com>
Cc: magma@ietf.org
Subject: Re: [magma] Question about proxy implemenation in RFC 4605
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Hi Kunan,
 
RFC 4605 refers to RFC 3376 for this:
 
>From RFC 4605. (4.1)
The membership database is a set of membership records of the form:
   (multicast-address, filter-mode, source-list)
   Each record is the result of the merge of all subscriptions for that
   record's multicast-address on downstream interfaces.  If some
   subscriptions are IGMPv1 or IGMPv2/MLDv1 subscriptions, these
   subscriptions are converted to IGMPv3/MLDv2 subscriptions.  The
   IGMPv3/MLDv2 and the converted subscriptions are first preprocessed
   to remove the timers in the subscriptions and, if the filter mode is
   EXCLUDE, to remove every source whose source timer > 0.  Then the
   preprocessed subscriptions are merged using the merging rules for
   multiple memberships on a single interface (specified in Section 3.2
   of the IGMPv3 specification [RFC3376] and in Section 4.2 of the MLDv2
   specification [MLDv2])
 
 
Section 3.2 of RFC 3376
 
 
3.2. Interface State
     In addition to the per-socket multicast reception state, a system
     must also maintain or compute multicast reception state for each of
     its interfaces.  That state conceptually consists of a set of
     records of the form:
        (multicast-address, filter-mode, source-list)
     At most one record per multicast-address exists for a given
     interface.  This per-interface state is derived from the per-socket
     state, but may differ from the per-socket state when different
     sockets have differing filter modes and/or source lists for the
     same multicast address and interface.  For example, suppose one
     application or process invokes the following operation on socket
     s1:
        IPMulticastListen ( s1, i, m, INCLUDE, {a, b, c} )
     requesting reception on interface i of packets sent to multicast
     address m, *only* if they come from source a, b, or c.  Suppose
     another application or process invokes the following operation on
     socket s2:
 
Cain, et. al.               Standards Track                     [Page 5]

RFC 3376                         IGMPv3                     October 2002

        IPMulticastListen ( s2, i, m, INCLUDE, {b, c, d} )
     requesting reception on the same interface i of packets sent to the
     same multicast address m, *only* if they come from sources b, c, or
     d.  In order to satisfy the reception requirements of both sockets,
     it is necessary for interface i to receive packets sent to m from
     any one of the sources a, b, c, or d.  Thus, in this example, the
     reception state of interface i for multicast address m has filter
     mode INCLUDE and source list {a, b, c, d}.
     After a multicast packet has been accepted from an interface by the
     IP layer, its subsequent delivery to the application or process
     listening on a particular socket depends on the multicast reception
     state of that socket [and possibly also on other conditions, such
     as what transport-layer port the socket is bound to].  So, in the
     above example, if a packet arrives on interface i, destined to
     multicast address m, with source address a, it will be delivered on
     socket s1 but not on socket s2.  Note that IGMP Queries and Reports
     are not subject to source filtering and must always be processed by
     hosts and routers.
     Filtering of packets based upon a socket's multicast reception
     state is a new feature of this service interface.  The previous
     service interface [RFC1112] described no filtering based upon
     multicast join state; rather, a join on a socket simply caused the
     host to join a group on the given interface, and packets destined
     for that group could be delivered to all sockets whether they had
     joined or not.
     The general rules for deriving the per-interface state from the
     per-socket state are as follows:  For each distinct (interface,
     multicast-address) pair that appears in any socket state, a per-
     interface record is created for that multicast address on that
     interface.  Considering all socket records containing the same
     (interface, multicast-address) pair,
   o if *any* such record has a filter mode of EXCLUDE, then the filter
     mode of the interface record is EXCLUDE, and the source list of the
     interface record is the intersection of the source lists of all
     socket records in EXCLUDE mode, minus those source addresses that
     appear in any socket record in INCLUDE mode.  For example, if the
     socket records for multicast address m on interface i are:
        from socket s1:  ( i, m, EXCLUDE, {a, b, c, d} )
        from socket s2:  ( i, m, EXCLUDE, {b, c, d, e} )
        from socket s3:  ( i, m, INCLUDE, {d, e, f} )
 
 
Cain, et. al.               Standards Track                     [Page 6]

RFC 3376                         IGMPv3                     October 2002

     then the corresponding interface record on interface i is:
                         ( m, EXCLUDE, {b, c} )
     If a fourth socket is added, such as:
        from socket s4:  ( i, m, EXCLUDE, {} )
     then the interface record becomes:
                         ( m, EXCLUDE, {} )
   o if *all* such records have a filter mode of INCLUDE, then the
     filter mode of the interface record is INCLUDE, and the source list
     of the interface record is the union of the source lists of all the
     socket records.  For example, if the socket records for multicast
     address m on interface i are:
        from socket s1:  ( i, m, INCLUDE, {a, b, c} )
        from socket s2:  ( i, m, INCLUDE, {b, c, d} )
        from socket s3:  ( i, m, INCLUDE, {e, f} )
     then the corresponding interface record on interface i is:
                         ( m, INCLUDE, {a, b, c, d, e, f} )
     An implementation MUST NOT use an EXCLUDE interface record to
     represent a group when all sockets for this group are in INCLUDE
     state.  If system resource limits are reached when an interface
     state source list is calculated, an error MUST be returned to the
     application which requested the operation.
   The above rules for deriving the interface state are (re-)evaluated
   whenever an IPMulticastListen invocation modifies the socket state by
   adding, deleting, or modifying a per-socket state record.  Note that
   a change  of socket state does not necessarily result in a change of
   interface state.
 
--------------
 
So I think just applying these rules there is no need for querys
 
Don't hesitate to contact me for a follow up
 
Alvaro


________________________________

De: Kunal Shah [mailto:kunal.shah@ericsson.com]
Enviado el: lun 01/11/2010 23:49
Para: Alvaro Fernandez
CC: magma@ietf.org
Asunto: RE: [magma] Question about proxy implemenation in RFC 4605


Hi Alvaro,
 
I dont think you have understood my question. The rules that you are suggesting from RFC 3376, are the rules used for aggregating the information on an interface with multiple sockets. What I am asking is what rules should be followed on a proxy device in order to aggregate the state of all the interfaces, after the state of one of the interfaces has changed. This is because, on a device doing proxy, the state that is created is an aggregate of the state of the interfaces; i.e the state that would exist if all the interfaces represented individual hosts on a single LAN. Now from RFC 3376, if a host goes away on an interface, there are certain rules that the router must follow regarding queries that need to be sent in order to arrive to the new state on that interface. My concern is, on a proxy device, if the same rules are followed, queries will need to be sent out on all the interfaces in order to make sure that the new state reflects the state of all the interfaces. This might not be efficient/scalable if the proxy device has interfaces in the order of hundreds. 
 
Or I have not understood the RFC 4605 correctly...
 
Kunal
 
________________________________

From: Alvaro Fernandez [mailto:Alvaro@soportemv.com] 
Sent: Monday, November 01, 2010 2:19 PM
To: Kunal Shah
Cc: magma@ietf.org
Subject: RE: [magma] Question about proxy implemenation in RFC 4605



Hi Kunai,

I thing my previous Mail was wrong. I was thinking in once interface with múltiple host and this is not your question.

The proxy should apply same rules  explained inRFC3376 in the función IPMulticastListen when there are different sockets using the same multicast group.

I think there is no need for queries, just apply these rules.

Hope this will help

Álvaro

-----Mensaje original-----
De: Kunal Shah [mailto:kunal.shah@ericsson.com]
Enviado el: lun 01/11/2010 19:30
Para: Alvaro Fernandez
CC: magma@ietf.org
Asunto: RE: [magma] Question about proxy implemenation in RFC 4605

Hi Alvaro,

For a router to determine that there are no interested hosts on the LAN, it does send out group specific or source-group specific queries. Does this mean, that the proxy device should send out source-group specific queries on other interfaces when deemed required?? How will this scale if there are a large number of interfaces??

Kunal

________________________________
From: Alvaro Fernandez [mailto:Alvaro@soportemv.com]
Sent: Saturday, October 30, 2010 10:36 AM
To: Kunal Shah
Cc: magma@ietf.org
Subject: RE: [magma] Question about proxy implemenation in RFC 4605


Hi Kunal

I read it years ago but I think RFC 4605 explains that the downstream network interface should behave like a router, so the solution is in the state machine explained in RFC3376 for the IGMPv3 router

Álvaro


-----Mensaje original-----
De: magma-bounces@ietf.org en nombre de Kunal Shah
Enviado el: sáb 30/10/2010 2:46
Para: magma@ietf.org
Asunto: [magma] Question about proxy implemenation in RFC 4605

Hi all,

According to RFC 4605, a router creates a membership database after merging the subscriptions on individual interfaces. Lets say that 3 IGMPv3 capable interfaces are as follows:

Interface 1 has host reporting Include S1 -> I(S1)
Interface 2 has host reporting Exclude S2 -> E(0,S2)
Interface 3 has host reporting Exclude nothing -> E(0,0)

For a device doing IGMPv3 proxy, the final membership record for group G is (G, EXCLUDE, NULL). Now lets say the host on interface 3 goes away, because of which the subscription on interface 3 would expire and there wont be any IGMPv3 state on interface 3.  How would the new membership record for PROXY be calculated?? The RFC does not suggest any way to do this. Would IGMP process have to go through each interface again and then recompute the new membership record?? This would be very inefficient especially if there are multiple interfaces.
Is there a better way to recompute the new membership record??


Thanks
Kunal