Dell PowerConnect 8100 User's Configuration Guide - Page 950
Flood Blocking, interface. Allowing interface-scope LSAs on blocked interfaces allows graceful
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Flood Blocking OSPF is a link state routing protocol. Routers describe their local environment in Link State Advertisements (LSAs), which are distributed throughout an area or OSPF domain. Through this process, each router learns enough information to compute a set of routes consistent with the routes computed by all other routers. Normally, OSPF floods an LSA on all interfaces within the LSA's flooding scope. Flooding ensures that all routers receive all LSAs. A router normally receives a duplicate copy of each LSA once on each interface in the LSA's flooding scope. The duplicate deliveries make OSPF LSA distribution robust, but in highly interconnected networks, can cause a lot of buffer and CPU usage. Buffer and CPU use can be reduced by selectively blocking LSA flooding on some interfaces, while ensuring that LSAs are flooded on enough interfaces to guarantee delivery of all LSAs to all routers. When enabling flood blocking, the network administrator must ensure there is sufficient LSA flooding even when there are router and link failures. This feature enables a network administrator to disable LSA flooding on an interface. Flood blocking only affects flooding of LSAs with area or AS (i.e., domain-wide) scope. Such LSAs are expected to be flooded to neighbors on other, unblocked interfaces, and eventually reach neighbors on blocked interfaces. An LSA with interface flooding scope cannot be blocked; there is no other way for interface-scope LSAs to reach neighbors on the blocked interface. Allowing interface-scope LSAs on blocked interfaces allows graceful restart to work, even if the restarting router has neighbors on flood blocked interfaces. When an interface is blocked, LSAs with area or AS scope are not sent to any neighbor on that interface. When flood blocking is enabled, OSPF does not advertise any LSAs with area or AS scope in its database description packets sent to neighbors on a blocked interface. When OSPF receives an LSA from a neighbor and the local database copy is newer than the received LSA, OSPF normally sends the newer LSA directly to the neighbor. If the neighbor is on a blocked interface, OSPF neither acknowledges the LSA nor sends the newer LSA. Instead, OSPF expects that the neighbor will receive the newer LSA indirectly. Flooding is enabled by default. 950 Configuring OSPF and OSPFv3
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1,187
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1,188
-
1,189
-
1,190
-
1,191
-
1,192
-
1,193
-
1,194
-
1,195
-
1,196
-
1,197
-
1,198
-
1,199
-
1,200
-
1,201
-
1,202
-
1,203
-
1,204
-
1,205
-
1,206
-
1,207
-
1,208
-
1,209
-
1,210
-
1,211
-
1,212
-
1,213
-
1,214
-
1,215
-
1,216
-
1,217
-
1,218
-
1,219
-
1,220
-
1,221
-
1,222
-
1,223
-
1,224
-
1,225
-
1,226
-
1,227
-
1,228
-
1,229
-
1,230
-
1,231
-
1,232
-
1,233
-
1,234
-
1,235
-
1,236
-
1,237
-
1,238
-
1,239
-
1,240
-
1,241
-
1,242
-
1,243
-
1,244
-
1,245
-
1,246
-
1,247
-
1,248
-
1,249
-
1,250
-
1,251
-
1,252
-
1,253
-
1,254
-
1,255
-
1,256
-
1,257
-
1,258
-
1,259
-
1,260
-
1,261
-
1,262
-
1,263
-
1,264
-
1,265
-
1,266
-
1,267
-
1,268
-
1,269
-
1,270
-
1,271
-
1,272
-
1,273
-
1,274
-
1,275
-
1,276
-
1,277
-
1,278
-
1,279
-
1,280
-
1,281
-
1,282
-
1,283
-
1,284
-
1,285
-
1,286
-
1,287
-
1,288
-
1,289
-
1,290
-
1,291
-
1,292
-
1,293
-
1,294