Re: danger of bridges


Stu Grossman (GROSSMAN@Sierra.Stanford.EDU)
Tue 31 Mar 87 16:56:55-PST


Good guesswork! Endnodes do indeed listen to a special multicast address.

A breif explanation: When a DECnet endnode wants to send a datagram, it
sends it to a DECnet node known as the 'Designated Router'. The
designated router is known by the endnode because he periodically emits a
special hello message to say who he is. Now, theres a little bit more glue
and filler to deal with getting the endnode to use a more direct route if
possible (such as if the dest node is on the same ethernet), and cacheing
of the next hop (ie: best gateway) to get to a specified node.

Just to throw another monkey into the wrenchworks, there is the added
feature that the designated router can move around! There's a little bit
of protocol and stuff that arbitrates who gets the honor, but theres no
special setup needed to establish the DR. Oh yeah, just one more thing,
just in case there is NO DR at all, the endnode can still talk to other
systems on the same wire, it just computes the Ethernet address from
the DECnet address, and sends the datagram!

        Stu Grossman
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