RE: Multicast Subscription per IP:Port

Lefe,

        While IP address of the multicast group is used in join processes
when host decides to receive multicast traffic, the port number is a host
specific parameter allocated in the OS kernel tables to split data streams
between different instances on the host. It will be the task of the host
network stack to separate different ports, routers would not know who is
listening on which port on multiple hosts and do not keep the common view of
their L3 network usage parameters.

        This is the reason why increment by IP is a much more preferred
method versus increment by port in multicast dense deployments, including
voice and video.

        When multicast is necessary on the socket, kernel receives two calls
- setsockopt() to add multicast membership with IP_ADD_MEMBERSHIP option,
followed by bind() to link the socket with the operating interface. After
that interface will receive all multicast traffic on the group address and
pass through only packets that the host has been subscribed to.

        Furthermore, IGMP packet does not have a field for port number.

Hope this helps,

Adel Abouchaev, CCIE# 12037, CISSP, MCSE

Technical Support Engineer
Netmasterclass LLC, Cisco Learning Partner
RFC821: adel_at_netmasterclass.net
E.164: +18886772669
HTTP: www.netmasterclass.net

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Lefe
De Meedorf
Sent: Wednesday, November 03, 2010 5:44 AM
To: Cisco certification
Subject: OT: Multicast Subscription per IP:Port

Dear All,

Can client subscribe to multi-casting server per port basis ? How can
we restrict multicast clients per port ?

e.g.

<CLIENT> ---------- <SWITCH> ------------- <ROUTING DOMAIN>
--------------- <SERVER>

Server has two multicast applications sending multicast out on
225.5.5.5:1000 and 225.5.5.5:2000.

When CLIENT subscribe for 225.5.5.5:2000, will CLIENT implicitly
receive 225.5.5.5:1000 packets also ?
If not, how can we configure per port restriction ?

Thanks

-- 
Lefe De Meedorf
Blogs and organic groups at http://www.ccie.net