Table of contents
The initial metric value imported by the route
Deepen the concept of routing introduction
One-point one-way import scene
Routing import concept
basic concept
Route introduction (import injection, redistribute republish)
Why is it necessary to import
Due to the differences in routing algorithms, mechanisms, and overheads between different routing protocols, different routing protocols cannot directly share each other's routes; at this time, it is necessary to import routes from one routing protocol to another routing protocol through route import technology It can also be introduced between the same routing protocols
Principles of Route Import
Import the active route of a certain protocol (that is, the imported route must exist in the routing table ) to another routing protocol on the importing router
Precautions
The router performing the import must run these two/multiple routing protocols at the same time before it can perform the import
The router responsible for importing will not change its own routing table. Importing is outward, only changing others, not itself
When routing is imported, problems such as suboptimal paths and routing loops may occur (common solutions include modifying routing priority, routing Cost, routing Tag, etc.)
Assuming that routing protocol A is imported to routing protocol B, which routes will be imported into B
The routes learned from protocol A will be imported into protocol B
The network route where the interface with protocol A enabled will be imported into protocol B
The initial metric value imported by the route
- Introduce other protocols to OSPF, the default cost is 1, Type2, route priority is 150 (the initial metric value can be modified by default cost)
- Introduce other protocols to ISIS, the default cost is 0, Level-2, and the routing priority is 15 (the initial metric value can be modified by default cost)
- Introduce other protocols to BGP, the default cost is the metric value of IGP, and the route priority is 255 (you can modify the initial metric value through default med)
Deepen the concept of routing introduction
Import routes on AR10
Import RIP routes into ISIS, and then import ISIS into OSPF
At this time, AR11 can learn the route of that network segment (only the routes of 30.1.1.0/24 and 13.13.13.13 can be learned)
Introduce RIP to ISIS, so that AR13 can learn the route of RIP through ISIS;
Because it is imported on AR10, the route about ISIS after the import of AR10 is the same as the route about ISIS before the import, and there are only routes 30.1.1.0/24 and 13.13.13.13
Now import ISIS to OSPF on AR10, OSPF can only learn the routes of 30.1.1.0/24 and 13.13.13.13, but cannot learn the routes of 20.1.1.0/24 and 12.12.12.12
Import RIP routes into ISIS on AR13
On AR10 and then introduce ISIS into OSPF
At this time, AR11 can learn the route of that network segment (it can learn the route of 30.1.1.0/24, 20.1.1.0/24, 13.13.13.13, 12.12.12.12)
Import RIP to ISIS on AR13. At this time, AR10 has learned the routes of 20.1.1.0/24 and 12.12.12.12 in the routing table of ISIS.
Import ISIS to OSPF on AR10, and AR11 can learn the routes of 30.1.1.0/24, 20.1.1.0/24, 12.12.12.12, and 13.13.13.13
Ways of importing routes
Single-point two-way routing import
Single-point one-way route import (default route needs to be delivered to achieve mutual access)
Multi-point two-way routing import (here is two-point two-way)
Importing multipoint unidirectional routes
Same as single-point one-way, need to issue default route to achieve mutual access
Route import scenario
One-point one-way import scene
What is one-point one-way
Single-point one-way: import a protocol route to another protocol route on one device
Potential problems caused by one-point one-way - sub-optimal path
In the single-point one-way import scenario, if a low routing priority is introduced into a high routing priority, there may be a suboptimal path; if a high routing priority is introduced into a low routing priority, there will be no suboptimal path
suboptimal scenario
Introducing RIP into ISIS on AR5
AR4 and AR6 learned 7.7.7.7 through ISIS, and the priority is 15
AR6 has learned the route 7.7.7.7 through RIP before AR5 imports the route, and the priority is 100; so after AR5 imports the route, it finds that the route 7.7.7.7 learned through ISIS has a higher priority
At this time, AR6 will use the route (AR6-AR4-AR5-AR7) learned by ISIS when accessing 7.7.7.7, resulting in a suboptimal path.
How to solve sub-optimal paths - by adjusting the priority of routes or filtering routes
1. On AR6, lower the priority of the routes imported from AR5 (lower than the priority of RIP routes, that is, adjust the priority value to higher than 100)
2. On the AR6, increase the priority of the route learned from RIP (higher than the route priority of ISIS, that is, adjust the priority value to less than 15)
3. Since AR6 already has RIP and ISIS addresses, it is possible to filter the routes imported from AR5
Two-point one-way import
What is a two-point one-way
Two-point one-way: On two devices, import a protocol route into another protocol route
Problems that may be caused by two-point one-way - it will cause suboptimal, routing feedback, and loop scenarios
In a two-point one-way introduction scenario, if a low routing priority is introduced into a high routing priority, there may be a suboptimal path; if a high routing priority is introduced into a low routing priority, there will be no suboptimal path
In the two-point one-way introduction scenario, there will be a route feedback scenario (R1 and AR2 devices run A protocol and B protocol at the same time, at this time, A is imported to B on AR1, and B is imported to A on AR2. The route learned by the protocol is introduced into the A protocol, which is called route feedback), if the route feedback phenomenon occurs, it may cause a loop
suboptimal scenario
In this scenario, only one of AR5 and AR6 will be suboptimal (specifically which one will be suboptimal depends on who introduces AR5 and AR6 first)
If AR5 introduces RIP to ISIS first, then AR6 introduces RIP to ISIS
At this time, AR5 introduces RIP to ISIS, causing AR6 to go to 7.7.7.7 suboptimal
At this time, AR6 does not have 7.7.7.7 in the RIP routing table, so at this time, 7.7.7.7 is not imported when RIP is imported into ISIS on AR6.
AR5 going to 7.7.7.7 is not suboptimal
How to solve sub-optimal paths - by adjusting the priority of routes or filtering routes
1. Modify the priority of the route imported from AR5 on AR6 (higher than the priority of ISIS route, that is, adjust the priority value to less than 15); modify the priority of the route imported from AR6 on AR5 (higher than ISIS route Priority, that is, adjust the priority value to less than 15)
2. Modify the priority of the routes imported from AR5 on AR6 (higher than the priority of ISIS routes, that is, adjust the priority value to less than 15); modify the priority of routes imported from AR6 on AR5 (higher than ISIS routes Priority, that is, adjust the priority value to less than 15)
3. Filter the routes imported by AR6 on AR5, and filter the routes imported by AR5 on AR6
Scenarios where suboptimal and loops exist at the same time
Introduce 8.8.8.8 into OSPF through Type2, set Cost to 2 (default is 1)
Then introduce OSPF into ISIS on AR5, and introduce ISIS into OSPF on AR6
Import 8.8.8.8 into OSPF; at this time, AR4, AR5, and AR6 learn the route of 8.8.8.8, the priority is 150, and the cost is 2; at this time, AR4, 5, and 6 access 8.8.8.8 to AR8, which is normal
Introduce OSPF to ISIS on AR5; at this time, AR6 learns the route of 8.8.8.8, and the priority is 15 (replace the previous priority of 150); at this time, AR6 accesses 8.8.8.8 to AR7, and AR6 accesses 8.8. 8.8 will cause a suboptimal path (a single point and one direction will cause a suboptimal path); AR4 and AR5 go to 8.8.8.8 or a normal path, no suboptimal path
Introduce ISIS into OSPF on AR6 (route feedback); at this time, AR6 learns the route to 8.8.8.8 from ISIS. When ISIS is introduced into OSPF, AR4 will learn 8.8.8.8 from AR6. Route with a priority of 150, a cost of 1, and a type of 2 (replace the previous route with a cost of 2 and a type of 2); at this time, when AR4 accesses 8.8.8.8, it goes to AR6, and when AR5 accesses 8.8.8.8, it goes to AR4. AR6 accesses 8.8.8.8 to AR5; in this scenario, a routing loop is formed
How to solve suboptimal and loop problems - through priority, filtering or Tag
1. Reduce the priority of the route imported from AR5 on AR6. At this time, AR6 will go to 8.8.8.8 and go to OSPF. Then, when ISIS is imported on AR6, the route of 8.8.8.8 will not be imported, avoiding routing loops with suboptimal
2. Filter the routes imported from AR5 on AR6. At this time, AR6 will go to 8.8.8.8 and go to OSPF. Then, when ISIS is imported on AR6, the routes of 8.8.8.8 will not be imported, avoiding routing loops and secondary excellent
3. Only using priority and filtering can solve the suboptimal and loop problems, but it cannot solve the problem of routing feedback. You can use tag technology to avoid routing feedback. Tag 10 when introducing OSPF into ISIS on AR5, and then add Tag 10 to AR6. When ISIS introduces OSPF, it refuses to introduce Tag 10; when ISIS is introduced into OSPF on AR6, Tag 20 is marked, and then when OSPF is introduced into ISIS on AR5, Tag 20 is rejected; at this time, there is no routing feedback
Note: Tag can only solve the routing feedback problem, but cannot solve the suboptimal path problem
Single-point two-way import
What is one-point two-way
Single-point bidirectional: On one device, import the route of protocol A into the route of protocol B, and then import the route of protocol B into the route of protocol A
Single-point bidirectional may cause suboptimal routing, and will not cause routing feedback
In a single-point multi-direction import scenario, if a low route priority is introduced into a high route priority, there may be a suboptimal path
Because the routing table on this device will not change when importing at a single point, so there will be no feedback when importing
suboptimal scenario
Announce 8.8.8.8 into OSPF on AR8, import ISIS into OSPF on AR5, and then import OSPF into ISIS
Introduce OSPF to ISIS on AR5, AR6 learns that 8.8.8.8 has higher priority through ISIS, and the next hop of AR6 to 8.8.8.8 is AR7
Import ISIS into OSPF on AR5. At this time, the routing table of ISIS on AR5 has no routes imported from OSPF. Therefore, when ISIS is imported into OSPF, no route feedback will occur.
Suboptimal paths can be resolved by prioritization, filtering
1. Lower the priority of routes imported from AR5 on AR6
2. On AR6, filter the routes imported by AR5
Two-point two-way import
What is a two-point two-way
Two-point bidirectional: On one device, import protocol A route into protocol B route, and then import protocol B route into protocol A route; on another device, import protocol A route into protocol B route , and then import the B protocol route into the A protocol route
Two-point two-way may cause suboptimal routing and routing loops, and there must be routing feedback
Depending on the order in which the introduction is made, the application location of the solution may change
Suboptimal and Loop Scenarios
Introduce 8.8.8.8 into OSPF through Type2, set Cost to 2 (default is 1)
Introduce OSPF into ISIS on AR5, then introduce ISIS into OSPF on AR6 (first)
Introduced OSPF into ISIS on AR6, then ISIS into OSPF on AR5 (after)
Introduce OSPF to ISIS on AR5, and then introduce ISIS to OSPF on AR6; this will cause suboptimal and loop (that is, multi-point one-way)
Introduce OSPF into ISIS on AR6, and then introduce ISIS into OSPF on AR5;
After solving the above problems, loops and sub-optimal problems will occur when importing at this time (the next hop of AR4 is AR5, and the next hop of AR5 is AR7);
And the purpose of multi-point two-way import is no longer to learn routes; it is for network reliability, so that the routes from AR4 to ISIS and from AR7 to OSPF have backup paths or load sharing
Since the route 8.8.8.8 of AR6 goes through ISIS, after AR6 introduces OSPF to ISIS, AR7 does not learn the route 6.6.6.6 from AR6; AR7 cannot load or has no backup for the route 8.8.8.8
When ISIS is introduced into OSPF on AR5, AR4 has multiple paths to ISIS
How to solve the problems of suboptimality, loops, and no backup path - through priority, filtering or Tag
1. On AR6, lower the priority of the route imported by AR5. At this time, AR6 will go to 8.8.8.8 through OSPF; on AR5, lower the priority of the route imported by AR6. At this time, when AR6 imports OSPF to ISIS, AR6 will also use OSPF. no suboptimal
2. On AR6, filter the routes imported by AR5. At this time, when AR6 goes to 8.8.8.8, OSPF is used; on AR5, filter the routes imported by AR6.
3. Only using priority and filtering can solve the suboptimal and loop problems, but it cannot solve the problem of routing feedback. You can use tag technology to avoid routing feedback. Tag 10 when introducing OSPF into ISIS on AR5, and then add Tag 10 to AR6. ISIS refused to introduce Tag 10 when introducing OSPF; tagged Tag 20 when introducing ISIS to OSPF on AR6, and then rejected Tag 20 when introducing OSPF to ISIS on AR5; tagged Tag 30 when introducing OSPF to ISIS on AR6, and then tagged on AR5 Refuse to introduce Tag 30 when introducing ISIS into OSPF; mark Tag 40 when introducing ISIS into OSPF on AR5, and then reject Tag 40 when introducing OSPF into ISIS on AR5;
The above method to solve the suboptimal and loop is not unique, but only lists the more commonly used methods, and the specific solution can be solved according to the on-site environment
Huawei's dual-point two -way routing introduction experimental configuration