Version 3.2/3.3 October 29, 1993ewlett-Packard Company
IP Variable Subnet Mask Support Training Paper Page 27
6.5 Addition of Subnet Mask Field to Routing Table Output
While not directly related to supporting a variable subnet
mask environment, the subnet mask associated with an IP
Route becomes more important in a variable subnet mask
environment, particularly as the new routing protocols such
as OSPF become widely deployed. Version 3.2/3.3 October 29, 1993ewlett-Packard Company
IP Variable Subnet Mask Support Training Paper Page 26
Each of the potential subnet changes has associated with it
a new topology event in NNM 3.3. These events are normal
events in the Configuration Events category, and are gen-
erated in the same format as other topology events. Further, by the assumptions above, netmon assumes a correct
subnet mask returned via SNMP, and uses that to create a new
subnet in NNM with the correct subnet mask. Normally, netmon would only
see the lowest level subnets, with the container subnets
being only conceptual in nature and used for summary rout-
ing. Th is da ta h as been w ritten by GSA Con te nt Generator DEMO!
Premature aging is also be used when unexpectedly receiving self-originated advertisements during the flooding procedure (see Section 13.4). A router may only prematurely age its own self-originated link state advertisements. The first stage of the procedure concerns only the transit vertices (routers and transit networks) and their connecting links. For example, the
class A networks 22.214.171.124 and 10.0.0.0 could have different
subnet masks even with the earliest versions of NNM. Automatic or manual splitting or merging of networks due
to changes in subnet masks in the user’s environment. I saw this statement: “ip subnet-zero //if router only has its subnet, it should not be used, so disable ip subnet zero” please tell me.. N6 RT7 / | N8 o o———o / | | | /| RT2 o o RT1 | | 2/ |9 / | | |RT8 / | /3 |3 RT11 o o o o / | | | N12 N15 N2 o o N1 1| |4 | | N9 o o N7 /| / | N11 RT9 / |RT12 o——–o——-o o——–o H1 3 | 10 |2 | o N10 Figure 5: The SPF tree for Router RT6 Edges that are not marked with a cost have a cost of of zero (these are network-to-router links). Content was cre ated by GSA Content Generator Demoversion!
Routes to networks belonging to other AS’es (such as N12) appear as dashed lines on the shortest path tree in Figure 5. Use of this externally derived routing information is considered in the next section. 2.2. Use of external routing information After the tree is created the external routing information is examined. The shortest-path tree for Router RT6 in our example is depicted in Figure 5. The tree gives the entire route to any destination network or host. This discovery is done during the calculation of Area A’s shortest-path tree (see Section 16.1). o To aid in the description of the algorithm, a new parameter has been added to the OSPF area structure: TransitCapability. For example, a change to an intra-area route will cause an area border router to originate new summary link advertisements (see Section 12.4). See Section 16.7 for a complete list of the OSPF protocol actions resulting from routing table changes. In our example, all the routers in the Autonomous System know that Router RT7 has two external routes, with metrics 2 and 9. OSPF supports two types of external metrics.
Processing of Type 2 external metrics is simpler. For the processing of external data, we note the next hop and distance to any router advertising external routes. Note that the presence of any link back to V is sufficient; it need not be the matching half of the link under consideration from V to W. This is enough to ensure that, before data traffic flows between a pair of neighboring routers, their link state databases will be synchronized. No protocol traffic at all will be sent or received on such a interface. The interface will be unavailable for regular data traffic. All interface timers should be disabled, and there should be no adjacencies associated with the interface. Adjacencies are established to all other routers attached to the network. DR In this state, this router itself is the Designated Router on the attached network. In this state, the router itself has not been selected Backup Designated Router either. The Backup Designated Router (if they exist). Waiting In this state, the router is trying to determine the identity of the (Backup) Designated Router for the network. Point-to-point In this state, the interface is operational, and connects either to a physical point-to-point network or to a virtual link.