All things related to multicast

[Bill Owens <>]

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.