29-08-2004, 06:12 PM
Chào các bạn, tôi có đọc quyển BSCI của Cisco Press. Phần giải thích hoạt động của OSPF tôi thấy khó hiểu chỗ này, mong được các bạn giải thích giúp:
Learning a New Route
When the 2500 router receives a network LSA update from the DR, it goes through the following logical steps:
1. The router takes the first entry from the update—the first network with information about the state of its link.
2. The router verifies that the type of LSA is one that can be accepted by this router.
3. Having ascertained that it is a valid LSA which it can receive, the router issues a lookup to its topological database.
4. If the LSA entry is not in the topological database, it is flooded immediately out all the OSPF interfaces, except for the receiving interface.
5. If the LSA entry is in the topological database, further questions are required.
6. The router determines whether the new LSA has a more recent (higher) sequence number.
7. If the sequence numbers are the same, the router calculates the checksum for the LSAs and uses the LSA with the higher checksum.
8. If the checksum numbers are the same, the router checks the MaxAge field to ascertain which is the most recent update.
9. Having found that the latest LSU is the one that was received, the router determines whether it has arrived outside the wait period, before another computation is allowed (minsLSarrival).
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Các bước từ 1 đến 5 thì mình đã hiểu. Thế còn bước 7,8,9 là để làm sao? Mong các bạn giải thích giúp.
Xin cảm ơn nhiều.
Learning a New Route
When the 2500 router receives a network LSA update from the DR, it goes through the following logical steps:
1. The router takes the first entry from the update—the first network with information about the state of its link.
2. The router verifies that the type of LSA is one that can be accepted by this router.
3. Having ascertained that it is a valid LSA which it can receive, the router issues a lookup to its topological database.
4. If the LSA entry is not in the topological database, it is flooded immediately out all the OSPF interfaces, except for the receiving interface.
5. If the LSA entry is in the topological database, further questions are required.
6. The router determines whether the new LSA has a more recent (higher) sequence number.
7. If the sequence numbers are the same, the router calculates the checksum for the LSAs and uses the LSA with the higher checksum.
8. If the checksum numbers are the same, the router checks the MaxAge field to ascertain which is the most recent update.
9. Having found that the latest LSU is the one that was received, the router determines whether it has arrived outside the wait period, before another computation is allowed (minsLSarrival).
....................
Các bước từ 1 đến 5 thì mình đã hiểu. Thế còn bước 7,8,9 là để làm sao? Mong các bạn giải thích giúp.
Xin cảm ơn nhiều.