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network
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...
There may not be a clear line between organizational and technical
reasons for renumbering. While networks have a charm and beauty all
their own, the organizational reasons should be defined first in
order to justify the budget for the technical renumbering. There
...
... installation of routers in a bridged legacy network. Organizations
may have had an adequate bridging solution that did not scale with
...
... numbering plan needs to work with
these new ideas. Legacy bridged networks and leading-edge workgroup
switched networks ...
... networks and leading-edge workgroup
switched networks may very well need changes in the subnetting
structure. Renumbering needs may also develop with the introduction
of new WAN ...
... routing.
Traditional bridged networks share many of the problems of workgroup
switches, but have additional performance problems when bridged ...
... Switches are commonly managed by SNMP applications. These network
management applications communicate with managed devices using IP.
Even if the switch ...
... traditional services. At first glance, when converting existing
enterprise networks to NBMA, it might appear that the existing subnet
structure should be preserved, but this is often not the case.
...
... assigned systematically. Systematic address space is rarely the case
in legacy networks.
...
... to successful renumbering. Begin by identifying the prefixes in or
planned into your network, and whether they have been assigned in a
systematic and hierarchical manner.
...
... a value in the most significant bit positions historically has been
called a "network number," when the assigned high-order part is 8,
16, or 24 bits long. More recent usage does not limit the assigned
...
... Even before CIDR, we collapsed multiple subnets into a single network
number advertisement sent to external routers. In a more general
...
... internal routing structure, and the changes only affect the
internal subnet structure of the enterprise network. This is typical
of efforts involved in increasing the number of available subnets
...
... ISP, who assigns address
space from a CIDR block rather than a classful network previously
used. With a different high-order prefix length, the enterprise
...
... default route to a higher-level,
better-connected router. This assumes a hierarchical network design,
which is generally desirable in the interest of scaling.
...
... address prefixes have been
assigned in a consistent and contiguous manner, which is often not
the case in legacy networks. Nevertheless, there is less to change
when we can refer to blocks of prefixes.
...
... systems of static routes. RIPv1 and IGRP do support classful
summarization (i.e., at Class A/B/C network boundaries only).
If existing addresses ...
... addresses have been assigned hierarchically, it may be
possible to renumber below the level of summarization, while hiding
the summarization to the rest of the network. In other words, if all
the address bits ...
...
Routers commonly communicate with an assortment of network management
and other infrastructural servers. Examples of these servers are
given in the "Network Management ...
... network management
and other infrastructural servers. Examples of these servers are
given in the "Network Management" section below. DNS itself,
however, may be an important exception.
...
... addresses stored in read-only memory (ROM). Using
LAAs solves the problem of MAC addresses changing when a network
interface card changes, but LAAs have their own management problems
of configuration into end systems and maintaining uniqueness within
...
... Network Address Translation ...
...
Network address translation (NAT) is a valuable technique for
renumbering, or even for avoiding the need to renumber significant
...
... parts of an enterprise [RFC1631]. It is not always transparent to
network layer protocols, upper layer protocols, and network
management tools ...
... network layer protocols, upper layer protocols, and network
management tools, and must not be regarded as a panacea.
...
... hosts could be assigned only global
addresses, if the network topology and routing plan permit.
...
... stub domains. This may in fact be desirable for
security, but may present network management problems. One
possibility would be to develop a NAT MIB ...
... RFC1812], and not assuming that a route to a "Class A/B/C network
number" implies routes to all subnets of that network ...
... network
number" implies routes to all subnets of that network. Assumptions
also should not be made that a prefix length is implied by the
...
... IP implementations.
When planning renumbering, network designers must know if the new
address has been allocated using CIDR ...
... In experimenting with the CIDR use of a former Class A network
number, it was shown in RFC1879 that CIDR ...
... Discontiguous Networks ...
... prefix addressing is that of
discontiguous networks. This problem is easy to create
inadvertently when renumbering. In the example below, assume the
...
... subnet of
10.0.0.0. We call this problem, when parts of the same classful
network are separated by different networks, discontigous subnets.
...
... 10.0.0.0. We call this problem, when parts of the same classful
network are separated by different networks, discontigous subnets.
...
... 10.0.0.0.
Another way to deal with the discontiguous network problem is to
assign secondary addresses in 10.0.0.0 to the R1 ...
... host is told its major (i.e.,
classful) network is not subnetted, even though the address plan
actually is subnetted, this will often persuade it to ARP ...
... architectures, notably DECnet, Banyan VINES, Xerox
Network Services, and IPX, may modify MAC addresses of routers ...
... address space is being recovered in an existing Class B network with
8 bits of subnetting. Certain /24 bit ...
... router, which one (if any) should/will respond to a ping? Other
network management mechanisms do not work cleanly with unnumbered
interface.
...
... traffic. In either case, extreme care must be taken in changing the
rules, to avoid leakage of sensitive information. denial of access
to legitimate users, or network congestion.
...
... "demilitarized zone (DMZ)," and the internal screening router between
the inside and the "perimeter network." Between these two networks
is the bastion host ...
... router between
the inside and the "perimeter network." Between these two networks
is the bastion host, in which reside various non-routing ...
... +-----------+ | | Host | | +-----------+ Internal
| +--------+ | +-----------+ Network
| +--------+ |---| Dialup |
...
... Address Space, as well
as address space from the enterprise's internal network. If the
internal network address ...
... address space from the enterprise's internal network. If the
internal network address changes, the inbound filters clearly will
...
... host also will need to change. Internal
screening routers permit access from the internal network to selected
servers on the perimeter network, as well as to the bastion host ...
... routers permit access from the internal network to selected
servers on the perimeter network, as well as to the bastion host
itself. If the enterprise uses private address space ...
... of the first interior routing protocols. It still does that job in
small networks, and also has been used for assorted functions that
are not strictly part of interior routing. In this discussion ...
... Where legacy support requirements dictate it be retained, it is
worthwhile to try to limit RIPv1 in "stub" parts of the network.
Vendor-specific mechanisms may be available to interface ...
... Network Management ...
...
This section is intended to deal with those parts of network
management that are intimately associated with routers, rather than a
general discussion ...
... ports, SNMP, and TFTP. Network management scripts may contain hard-
coded references to IP addresses supporting these services ...
... Performance information can be recorded in routers themselves, and
retrieved by network management scripts. Other performance
information may be sent to syslogd, or be kept in SNMP ...
...
Step 2--Design any needed topological changes. If temporary address
space, network address translators, etc., are needed, obtain
them.
...
... them.
Step 3--Install and test changes to make the network more
renumbering-friendly. These include making maximum use of
default routes ...
...
Step 4--Plan the actual renumbering. Should it be phased or total?
Can it be done in a series of stub network renumberings,
possibly with secondary addresses on core routers ...
...
Renumbering changes should be introduced with care into operational
networks. For changes to take effect, it is likely that at least
interfaces and probably routers ...
... Ferguson, P., and H. Berkowitz, "Network Renumbering Overview: Why would I want it and what is it anyway?", RFC 2071, January 1997. ...
... Egevang,, K., and P. Francis, "The IP Network Address Translator (NAT)", RFC 1631(-> 3022), May 1994. ...