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[Classful and Classless Routing] vs [classful routing và classless routing protocol]
Classful routing và classless routing khác hoàn toàn so với classful routing và classless routing protocol về mặt ý nghĩa. Thuật ngữ mà chúng ta đang phân tích ở đây chính là Classful routing và classless routing.
Mình xin trích đăng nguyên văn tiếng anh từ giáo trình "Cisco.Press.CCENT.CCNA.ICND2.Exam.Certificati on.G uide.2nd.Edition.Sep.2007.eBook-DDU.pdf" :
Hiện tại trong các IOS gần đây của Router chức năng ip classless luôn được enable default (tức là classless routing luôn được mặc định trong cấu hình ban đầu của Router).Do đó, trong môi trường LAB hiện nay , bạn sẽ ít khi nào gặp trường hợp giống như ví dụ bài LAB tôi đưa ở trên : có nghĩa là động tác ping 10.1.1.1 và 168.13.200.1 sẽ thành công.
Mọi người có thể xem ví dụ này :
Tôi xài Rip Version 1 (một classful routing protocol) nhưng tôi có enable bằng câu lệnh ip classless thì khi không tuyến nào trong bảng định tuyến thoả địa chỉ IP đích trong gói tin nó sẽ đưa đến default route.
Tuy nhiên nếu tôi dùng OSPF (một classless routing protocol) mà tôi disable bằng câu lệnh no ip classless thì khi đó router đã chuyển sang kiểu xử lí gói tin là classful routing , tức là :
+ Nếu như có 1 tuyến trong routing table có major network trùng với major network của địa chỉ đích trong gói tin nó sẽ drop packet đó.
+ Nếu như không có tuyến nào trong routing table có major network trùng với major network của địa chỉ đích trong gói tin thì nó sẽ forward gói tin đến default route.
Để hiểu rõ hơn về route types trong bảng định tuyến , các bạn có thể tham khảo ở link dưới đây :
Chúc các bạn luôn vui 1!!
Mình xin trích đăng nguyên văn tiếng anh từ giáo trình "Cisco.Press.CCENT.CCNA.ICND2.Exam.Certificati on.G uide.2nd.Edition.Sep.2007.eBook-DDU.pdf" :
Classful and Classless Routing
Cisco routers have two configurable options for how a router uses an existing default route: classless routing and classful routing.
=> Đây được xem như định nghĩa của classful and classless routing .
The terms classless and classful also characterize both IP addressing and IP routing protocols, so a fair amount of confusion exists as to the meaning of the terms. Before explaining the details of classful routing and classless routing, the next section summarizes the other use of these terms.
Summary of the Use of the Terms Classless and Classful
The terms classless addressing and classful addressing refer to two different ways to think about IP addresses. Both terms refer to a perspective on the structure of a subnetted IP address.
Classless addressing uses a two-part view of IP addresses, and classful addressing has a three-part view. With classful addressing, the address always has an 8-, 16-, or 24-bit network field, based on the Class A, B, and C addressing rules. The end of the address has a host part that uniquely identifies each host inside a subnet. The bits in between the network and host part comprise the third part, namely the subnet part of the address.
With classless addressing, the network and subnet parts from the classful view are combined into a single part, often called the subnet or prefix, with the address ending in the host part.
The terms classless routing protocol and classful routing protocol refer to features of different IP routing protocols. These features cannot be enabled or disabled; a routing protocol is, by its very nature, either classless or classful.
=> Được xem như là một định nghĩa đơn giản về classless routing protocols và Classful routing protocols
The third use of the terms classless and classful—the terms classful routing and classless routing—have to do with how the IP routing process makes use of the default route. Interestingly, this is the only one of the three uses of the terms that can be changed based on router configuration. Table 4-2 lists the three uses of the classless and classful terms, with a brief explanation. A more complete explanation of classless and classful routing follows the table.
Cisco routers have two configurable options for how a router uses an existing default route: classless routing and classful routing.
+ Classless routing causes a router to use its default routes for any packet that does not match some other route.
+ Classful routing places one restriction on when a router can use its default route, resulting in cases in which a router has a default route but the router chooses to discard a packet rather than forwarding the packet based on the default route.
+ Classful routing places one restriction on when a router can use its default route, resulting in cases in which a router has a default route but the router chooses to discard a packet rather than forwarding the packet based on the default route.
The terms classless and classful also characterize both IP addressing and IP routing protocols, so a fair amount of confusion exists as to the meaning of the terms. Before explaining the details of classful routing and classless routing, the next section summarizes the other use of these terms.
Summary of the Use of the Terms Classless and Classful
The terms classless addressing and classful addressing refer to two different ways to think about IP addresses. Both terms refer to a perspective on the structure of a subnetted IP address.
Classless addressing uses a two-part view of IP addresses, and classful addressing has a three-part view. With classful addressing, the address always has an 8-, 16-, or 24-bit network field, based on the Class A, B, and C addressing rules. The end of the address has a host part that uniquely identifies each host inside a subnet. The bits in between the network and host part comprise the third part, namely the subnet part of the address.
With classless addressing, the network and subnet parts from the classful view are combined into a single part, often called the subnet or prefix, with the address ending in the host part.
The terms classless routing protocol and classful routing protocol refer to features of different IP routing protocols. These features cannot be enabled or disabled; a routing protocol is, by its very nature, either classless or classful.
In particular, classless routing protocols advertise mask information for each subnet, giving classless protocols the ability to support both VLSM and route summarization.
Classful routing protocols do not advertise mask information, so they do not support VLSM or route summarization.
Classful routing protocols do not advertise mask information, so they do not support VLSM or route summarization.
The third use of the terms classless and classful—the terms classful routing and classless routing—have to do with how the IP routing process makes use of the default route. Interestingly, this is the only one of the three uses of the terms that can be changed based on router configuration. Table 4-2 lists the three uses of the classless and classful terms, with a brief explanation. A more complete explanation of classless and classful routing follows the table.
Mọi người có thể xem ví dụ này :
Tôi xài Rip Version 1 (một classful routing protocol) nhưng tôi có enable bằng câu lệnh ip classless thì khi không tuyến nào trong bảng định tuyến thoả địa chỉ IP đích trong gói tin nó sẽ đưa đến default route.
Tuy nhiên nếu tôi dùng OSPF (một classless routing protocol) mà tôi disable bằng câu lệnh no ip classless thì khi đó router đã chuyển sang kiểu xử lí gói tin là classful routing , tức là :
+ Nếu như có 1 tuyến trong routing table có major network trùng với major network của địa chỉ đích trong gói tin nó sẽ drop packet đó.
+ Nếu như không có tuyến nào trong routing table có major network trùng với major network của địa chỉ đích trong gói tin thì nó sẽ forward gói tin đến default route.
Để hiểu rõ hơn về route types trong bảng định tuyến , các bạn có thể tham khảo ở link dưới đây :
Chúc các bạn luôn vui 1!!