Blending DECnet Domains
DECnet has a 16-bit node address space with a fixed hierarchy of 6 bits of area
and 10 bits of node. By comparison, IP has a 32-bit node address space with a
flexible multilevel hierarchy. Many established networks have now grown to the
point where they use all 63 areas. The problem is that as different facilities connect
to each other, they want to connect their DECnet networks but cannot due to area
number conflicts.
The only solution is to redesign the DECnet architecture. (This is addressed by
DECnet Phase V.)However, by using area routing filters, it is possible to allow
some overlap between two DECnet domains.
Domain is not a standard DECnet term; it is used here as a name for a DECnet
wide-area network, presumably one with many areas. The goal is to blend two of
these domains, so that there is a common area that can reach parts of both
domains. However, there are more than 63 areas in the union of the two domains.
Because area filtering is not simple to administer and is restrictive, you should not
consider using it if there are enough area numbers available for the union of the
domains.
Toconfigure the overlap of two domains, first you must decide which areas to
intersect. These areas are the ones that will be able to participate in both domains.
These area numbers must not be used elsewhere in the two domains.
13.2 13.4
13.1
Eth/0
Eth/1
Area 7
Area 22
Area 11
Area 13
13.513.3
Figure 18. Example ofArea Routing Filter for Security
Using DNA IV
258 MRS V3.2 Protocol Config Ref Vol2