🚀 go-pugleaf

In article <1992Oct31.014819.16180@netcom.com>, seifert@netcom.com (Rich Seifert) writes:
> In article <1992Oct29.215308.15464@msuinfo.cl.msu.edu>, craven@egr.msu.edu (Dean Craven) writes:
> > Is there any protocol specification or vendor specific implementation
> > for tunneling source routed 802.5 frames through a FDDI or Ethernet
> > LAN?  That is, can two bridges, each attached to a 802.5 LAN, bridge
> > source routed frames across a FDDI/Ethernet LAN to/from 802.5 end
> > stations which only know how to source route?
> > 
> > Or, is this problem only ever solved by network layer routing?
> > 
> There is no need to tunnel at all. A source routing bridge connected
> between a Token Ring and an FDDI or Ethernet will talk correctly to
> another source routing bridge connected to the same LAN. That is, no
> special measures need to be taken to use an Ethernet or an FDDI as a
> backbone for source routed token rings.
> 
> It is important that there be no transparent bridges in the path between
> the source routing bridges. Transparent Bridges will not pass source
> routed frames.
> 
> Of course, there will be no connectivity to devices connected to the backbone.
> Neither Ethernet nor FDDI devices support source routing. Let's just
> hope that it won't cause them to crash--The problem area is when
> someone sends a frame to a multicast (or broadcast) with source routing
> enabled. The receiving Ethernet or FDDI station will see a source 
> address with the Routing Information Indicator set to one. This looks
> like a multicast source address, which is outlawed in Ethernet.
> 
> I don't believe this is a problem in practice. It may cause a counter
> to be bumped, but should not disrupt proper operation.


Well, some common FDDI MAC chips have a mode in which they ignore
any frames with the group bit set in the source address.


Vernon Schryver,   vjs@sgi.com