1. What are the network types of OSPF, and what is the default underlying architecture? Do you need to elect DR and BDR?
answer:
2. What are the message types and functions of OSPF?
Answer:
(1) Hello: discover, negotiate, and maintain OSPF neighbors;
(2) DD (Database Description): database description message, used to elect OSPF master and slave routers, carrying the summary of LSA;
(3) LSR (link state) request): Link status request message, requesting LSA information that the device lacks;
(4) LSU (link state update): link state update message, a message carrying LSA information .
- ① After receiving the LSR request message, LSU will reply;
- ②By default, the LSU message will be dynamically updated at a period of 1800s, and the dead time is 3600s
- ③When the network changes, it will also send out the LSU to update the link status (trigger the update);
(5) LSACK (link state ACK): link state information confirmation message, used to reply to confirm receipt of the LSU message, which carries the LSA digest;
3. What is the role of OSPF router ID and automatically generated rules?
Answer:
(1) The router ID identifies a router running the OSPF protocol and is used to elect DR/BDR.
(2) Rules for automatic generation of router ID:
Huawei standard : The IP address of the interface with the first UP status is used as the router id
RFC standard :
①Take the largest IP address of the loopback interface as the router ID;
②If there is no loopback interface, choose the largest physical interface IP address as the router ID.
4. What are the factors that affect the establishment of neighbors by OSPF? (List 7)
Answer: To
realize the establishment of OSPF neighbors, the following 7 conditions must be met:
- The version should be consistent,
- router ID cannot be the same,
- The area ID must be consistent,
- The authentication information must be consistent (including authentication-mode and password),
- hello/dead time should be consistent,
- The netmask must be consistent (required in broadcast and NBMA network types),
- The E bit and N bit of options must be the same.
5. As shown in the figure, AR1 and AR2 are running OSPF, the router id is 1.1.1.1 and 2.2.2.2, and AR2 is the DR, and other information is the default. Write the detailed information of the LSA between the AR1 and AR2 areas (LS type, LS ID, ADV, and the link type in the Router LSA).
Answer:
1, Router LSA
Router LSA
LS type of AR1 : router LSA
LS ID: 1.1.1.1 (local device router ID)
ADV: 1.1.1.1 (local device router ID)
link type: TransNet
link id: 10.1.12.2 (DR interface IP address)
link data: 10.1.12.1 (IP address of the local interface)
metric: 1
Router LSA
LS type of AR2 : router LSA
LS ID: 2.2.2.2 (local device route ID)
ADV: 2.2.2.2 (local device route ID)
Link type: TransNet
link id: 10.1.12.2 (DR interface IP address)
link data: 10.1.12.2 (IP address of the local interface)
Metric: 1
2. Network LSA of
AR2 (DR router):
LS type: Network LSA
LS ID: 10.1.12.2 (DR interface IP address)
ADV: 2.2.2.2 (DR router ID)
attached router: 1.1.1.1
attached router: 2.2.2.2
6. As shown in the figure, introduce loopback0 of AR1 (router id: 1.1.1.1) into OSPF, and other information is the default. Write down the contents of the 5 types of LSA after the introduction.
answer:
① LS type: AS external LSA
② LS ID: 192.168.1.1 (imported external routing network segment)
③ Netmask: 255.255.255.255
④ ADV: 1.1.1.1 (DR router ID)
⑤ Forwarding address: 0.0.0.0
⑥ E type : 2 (The default cost type is 2)
⑦ tag: 1 (The default tag is 1)
7. The role of forwarding address in the five types of LSA, under what circumstances is not 0.0.0.0
Answer: **
forwarding address can prevent sub-optimal path
If it is not 0.0.0.0:
(1) The interface connected to the imported external route is of the MA network type;
(2) The interface connected to the imported external route cannot be silent;
(3) The interface connected to the imported external route needs to be announced Into OSPF;
8. What are the special areas of OSPF, and what are their characteristics?
answer:
9. What are the components of the ISIS NET address and what are their functions?
answer:
The NET address of ISIS runs on the IP protocol and consists of three parts: SEL, system ID, and area ID.
The functions of the various components of NET are as follows:
1. SEL: can be used to express the protocol used by the upper layer, the default is 00 (representing running on the IP protocol);
2. system ID: equivalent to the router id of the device, with identification ; (The size is fixed at 6B)
3. Area ID: Indicate which ISIS area the device belongs to.
10. What are the types of ISIS routers and what are their characteristics?
Answer:
ISIS router types and their characteristics:
(1) Level-1: non-backbone area equipment, only the LSDB of this area exists (only neighbors can be established with equipment with the same area ID, and the area ID must be consistent when establishing adjacency relations);
(2) Level-2: Backbone area equipment, with LSDBs in all areas;
(3) Level-1-2 (default type): equipment that works in both the backbone area and non-backbone area. It can establish adjacency relationship with level-1 and level-2;
PS: When establishing adjacency with level-1, the area ID must be consistent;
11. Under what circumstances will ISIS's DIS be generated, how is it selected, and what is the difference between OSPF's DR?
answer:
The generation of
ISIS DIS : How to elect the ISIS DIS generated when the network type is a broadcast network :
(1) Compare priority priority, range: 0-127, default priority is 64, the larger the better;
(2) Compare the interface MAC address, the bigger the better;
The difference between ISIS's DIS and OSPF's DR :
12. How to synchronize LSDB with different network types of ISIS?
Answer:
ISIS synchronizes LSDB under P2P network type :
ISIS synchronizes the LSDB under the MA network type :
13. What is the difference between OSPF and ISIS?
Answer:
(1) Comparison of basic points
- OSPF supports areas : backbone area, common area and special area, the division of areas is more hierarchical, suitable for hierarchical deployment of enterprise networks
- ISIS support area : L2 and L1 area (L1 area is similar to the special area of OSPF), which is more suitable for operators to do flat network deployment
(2) Comparison of adjacency
(3) Comparison of LSDB synchronization process
(4) Comparison of routing calculation process
