First, OSPF ProcessID locally valid first, make it clear that the OSPF ProcessID, with a range of 1-65535, is used to identify the OSPF process locally on the router. Look, R1 uses process Number 10 to create an OSPF process while declaring its own straight connector, while R2 uses process number 20 to create an OSPF process and also declares its own straight connector. Although the two process numbers are different, we say that the OSPF process number is only valid locally, meaning that for R1 it is not concerned with what the OSPF process number, 10, 20, is used by its direct-attached OSPF neighbor-R2, which is a bit like "own thing to know"-locally valid. Of course, in the actual deployment, we are particularly recommended to use the same process number throughout the network (although you can try to use a different process number on each router, which certainly does not affect the operation of the network, but ...) You don't really do this, do you? )
two or one routers can create multiple OSPF processes, differentiate using OSPF processid, and separate processes from each other we'll see.
This diagram is interesting, in R2, the general practice is to create an OSPF process with a process number, while declaring your own two straight connections into this OSPF process, but in order to explain the local meaning of the OSPF process ID, I use two OSPF on the R2 ProcessID created two OSPF processes and declared the R2 straight connector, in other words, R2 uses OSPF process 20 to establish a neighbor relationship with R1, using OSPF process 30 to establish an OSPF neighbor relationship with R3. As a result , R2 has two OSPF processes locally, using ProcessID 20 and 30 to differentiate, which is the local meaning of the process number. then both processes will learn from their neighbors R1 and R2 to OSPF routes, but it is worth emphasizing that:
- These two OSPF processes are independent of each other, in other words, the OSPF route that R2 learns from R1 through the OSPF process 20 (which, strictly speaking, should be LSA), such as 1.1.1.0/24, is not directly updated to R3 by default (this is because in R2, these two OSPF processes are isolated from each other independently), Of course, from the R3 updated OSPF route, R2 Although he can learn, but, so will not be passed to R1, it is like, these two processes, although all in R2, but there are so little estrangement, the world's furthest distance, is this ah.
- Furthermore, R2 the two OSPF processes, though isolated from each other, can contribute routes for R2 itself, such as if R1 updates a route 1.1.1.0,R3 update over a 3.3.3.0, then the Global routing table in R2 can see both routes. And we said above, these two routes, will not be poured into each other's OSPF process (resulting in direct result is R1 no R3 route, R3 no R1 route), unless---------------------Yes, you know.
- As mentioned above, both processes can contribute routing entries for the R2 Global routing table, but one thing to note is, if R1 and R3 all update to R2, the same OSPF route? Who will R2 be preferred? Recall our situation in a single process, R2 will be based on cost to choose, if equivalent, R2 will load balance the two routes, right? But here is not the same, in this environment, R2 will be "first come first served" principle, who's routing first come over, I preferred who, so run fast or can Rob sister paper.
Three, summary
- OSPF ProcessID is only locally valid and is used to differentiate between different OSPF processes locally
- Although OSPF ProcessID is valid locally, we still recommend that the entire network use a consistent OSPF process ID unless there is a special need, which will facilitate network management and maintenance
- Under what circumstances would a multi-OSPF process be used? This is a big problem, in general, a router to create an OSPF process to achieve network requirements, but in some special, complex environment, a single OSPF process may not meet the requirements, so on a router to create multiple OSPF processes, so the direct benefit is that This router from the original cock silk role--ospf Interarea Router, gorgeous turned into a asbr, it can be re-released between processes, can filter routes or LSA, can manipulate routes, can do route-map-based policies, can do a route summary, and so on.
OSPF ProcessID (Process number) detailed
