All things related to multicast

[Alan Crosswell <>]

Oh, now I get it.  It's like link-local but for round-earth society members who 
might want to extend the scope of that just a teeny bit more than a single 
subnet.  So probably we should "declare" that in our domain, 239.255/16's scope 
is in fact link-local by setting up some ACLs.  I hadn't realized 239 was 
further subdivided.
/a

Bill Owens wrote:
> At 18:30 -0400 9/4/03, Alan Crosswell wrote:
>
> > Speaking of BCP filtering, look at all this clutter I am getting from 
> > hundreds of hosts campus-wide:
> >
> > Frame 1 (175 bytes on wire, 175 bytes captured)
> > Ethernet II, Src: 00:08:7c:d0:08:40, Dst: 01:00:5e:7f:ff:fa
> > Internet Protocol, Src Addr: 128.59.193.116 (128.59.193.116), Dst 
> > Addr: 239.255.
> > 255.250 (239.255.255.250)
> > User Datagram Protocol, Src Port: 3005 (3005), Dst Port: 1900 (1900)
> > Hypertext Transfer Protocol
> >     M-SEARCH * HTTP/1.1\r\n
> >         Request Method: M-SEARCH
> >     Host:239.255.255.250:1900\r\n
> >     ST:urn:schemas-upnp-org:device:InternetGatewayDevice:1\r\n
> >     Man:"ssdp:discover"\r\n
> >     MX:3\r\n
> >     \r\n
>
>
> Apparently SSDP is a quasi-standard protocol, based on a now expired I-D 
> that's still available at the UPnP site: 
> http://www.upnp.org/download/draft_cai_ssdp_v1_03.txt
>
> At least it uses an official multicast address ;) It sounds like this 
> traffic ought to be scoped to just the local subnet, though I may not 
> fully understand the relevant paragraph from RFC 2365:
>
> 6.1. The IPv4 Local Scope -- 239.255.0.0/16
>
>    239.255.0.0/16 is defined to be the IPv4 Local Scope.  The Local
>    Scope is the minimal enclosing scope, and hence is not further
>    divisible. Although the exact extent of a Local Scope is site
>    dependent, locally scoped regions must obey certain topological
>    constraints. In particular, a Local Scope must not span any other
>    scope boundary. Further, a Local Scope must be completely contained
>    within or equal to any larger scope. In the event that scope regions
>    overlap in area, the area of overlap must be in its own local scope.
>    This implies that any scope boundary is also a boundary for the Local
>    Scope. The more general topological requirements for administratively
>    scoped regions are discussed below.
>
> Talk about making your head hurt. . .
>
> Bill.