HP 200 Series Services And Applications page 172
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Also See for 200 Series:
- Installation manual (144 pages) ,
- Hardware support document (95 pages) ,
- Instructions manual (7 pages)
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DECnet Routing Service
Designated Router
Designated Router
DECnet end nodes always reside on LANs, and each maintains an
"on-Ethernet cache" of other nodes on its LAN. When an end node sends
packets destined for a node on a remote LAN (a node that is not in the
cache), the packets are sent to the "designated router". The designated
router routes packets on behalf of the end nodes. On each Ethernet,
one router is elected as the designated router. If the end node has not
learned the identity of the designated router, usually because no routers are
present on that LAN, the end node will attempt to send the packet directly to
the destination node.
When there are multiple routers on a LAN, one will be elected as the
designated router. To control which router is elected, configure the Router
Priority parameter on each network interface on each router. The router that
is assigned the highest priority relative to the other routers on the LAN will
be elected the designated router for that LAN. If there are routers with
equally high priority, the router with the highest node number will be elected
as the designated router. Note that a router that is connected to multiple
LANs may be the designated router on some LANs but not on others. A
designated router will be elected even if there are no end nodes currently on
the Ethernet. In figure 1, designated router ports for each Ethernet LAN are
highlighted with an asterisk (*).
Adjacency and Initialization
Before an end node can send packets through a DECnet router, the node
must establish an adjacency with that router. Additionally, routers must
establish adjacencies with one another before they can transfer packets
between them. All nodes (end nodes and routers) on a LAN with a router
establish adjacencies with that router. Two routers connected through a
point-to-point WAN link establish an adjacency. Two or more routers
connected to a common X.25 network (using X.25 point-to-point circuits)
establish adjacencies with one another. Routers maintain a database of
adjacent end nodes and routers. This is some of the information that is
represented in the DECnet routing tables.
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