HP 200 Series Services And Applications page 97

Bridging Service
Source-Routing Bridging
The HP router receives this frame from ring 4 and learns that to get from the
router to ring 5 through bridge 4, it needs to send the frame through ring 4.
The router overwrites the internal LAN ID in the RIF with the outgoing ring
that it learned when the frame first came through. It then overwrites the
incoming ring, in the case ring 4, with the internal LAN ID and sends it
through ring 2. The RIF at ring 2 is then 8AF0 0011 0023 0034 0050. End node
1 saves this RIF as the path to end node 2.
Partial, Full, and No Reduction
The setting of the Bridge ID configuration parameter affects how the two
source-routing algorithms record hops. Both the standard algorithm and
HP's hop count reduction algorithm work with the Routing Information Field
(RIF) in a source-routed frame's MAC header. The RIF is the part of the
frame containing the path between source and destination end nodes. (For
more information on bridge IDs, see an earlier section of this note, "How
Source Routing Works" and the next section on configuration.)
In a network with multiple bridges, when Hop Count Reduction is off and
each router's bridge ID is different, there is a routing designator pair for
every LAN or ring (incoming and outgoing path) and for every bridge (an
internal path identifying a virtual LAN and the bridge). All the bridges use up
RIF space. There is no hop count reduction.
With consecutive bridging HP routers, when Hop Count Reduction is off and
each router's bridge ID is the same, then only the first of the bridges uses up
RIF space with its virtual, internal LAN ID. This is partial hop count reduc-
tion.
With consecutive bridging HP routers, with Hop Count Reduction set to Yes,
whether the bridge IDs are identical or not makes no difference. None of the
internal LANs for bridges take up RIF space. In addition, all routing designa-
tors for the actual LANs or rings between the consecutive bridges are dis-
carded also. This is total hop count reduction.
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