Routes imported into IS-IS are invalid on S series switches

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Q: Why are routes imported into IS-IS invalid?
A: For S series switches supporting IS-IS, if the IS-IS level is not set when routes are imported into IS-IS, level-2 IS-IS is used by default. That is, routes are imported into level-2 IS-IS. To import routes to areas of other levels, specify the area level.

Other related questions:
Why is an OSPF route on an S series switch in the Invalid Adv state
Question: Why is an OSPF route in the Invalid Adv state? Answer: After you run the display ip routing-table x.x.x.x verbose command on an S series switch supporting OSPF to check information about a specified route, you may find that Invalid Adv is displayed in the State field. Possible causes are as follows: A route with a smaller preference value, for example, a directly connected route, exists. The route is filtered out based on a filter policy. A sham link is configured on the outbound interface.

Precedence of external routes imported by OSPF on S series switches
When an S series switch runs OSPF, you can run the import-route command in the OSPF process view to import external routes. The routes imported using this method are OSPF ASE routes and default precedence is 150.

How to configure BGP to import routes for S series switches
Background BGP itself cannot discover routes. Therefore, it needs to import other protocol routes, such as IGP routes, to the BGP routing table. In this manner, these imported routes can be transmitted within an AS or between ASs. BGP imports routes in either of the following ways: In import mode, BGP imports routes according to protocol types, such as RIP routes, OSPF routes, and IS-IS routes. To ensure validity of imported IGP routes, BGP can also import static routes and direct routes in import mode. In network mode, BGP imports routes in an IP routing table one by one, making it more precise than the import mode. Procedure Import mode: [HUAWEI] bgp 100 [HUAWEI-bgp] ipv4-family unicast //The IPv4 address family view is displayed. You can also enter other views as required. [HUAWEI-bgp-af-ipv4] import-rout static //Importing static routes is taken as an example. Importing routes of other protocols is similar. (Optional) Run the default-route import command to allow BGP to import the default route that already exists in the local IP routing table. By default, BGP does not add default routes to the BGP routing table. Network mode: [HUAWEI] bgp 100 [HUAWEI-bgp] ipv4-family unicast //The IPv4 address family view is displayed. You can also enter other views as required. [HUAWEI-bgp-af-ipv4] network 192.168.100.0 24 //Advertise routes to network segment 192.168.100.0 24. Precaution The network command is used to advertise exactly matched routes. That is, the routes whose destination addresses and prefix lengths exactly match the entries in the local routing table. If the network mask is not specified, routes are exactly matched according to the natural network segment. When using the undo network command to clear the existing configuration, you need to specify the correct mask.

Set the maximum number of routes imported by OSPF on S series switches
On S series switches, when the number of external LSAs (Type 5 and Type 7 LSAs) imported by OSPF exceeds the limit allowed by overflow, the excessive external LSAs cannot be processed properly and are discarded. To address the problem, run the lsdb-overflow-limit command in the OSPF process view to set the maximum of external LSAs in an LSDB. By default, the maximum number of external LSAs in the LSDB is not set. For example, set the maximum number of external LSAs in an LSDB to 400000 as follows: [HUAWEI] ospf 100 [HUAWEI-ospf-100] lsdb-overflow-limit 400000

Why imported external routes are not displayed in the LSDB on an S series switch
Perform the following operations on the S series switch to solve the problem. Run the display ospf interface command to check whether the interface that imports external routes is in the Up state. Run the display ospf brief command to check whether the device that imports external routes belongs to the stub area. Check whether the neighbor status is Full if external routes are learned from a neighbor. Check whether the lsdb-overflow-limit command is configured, and whether the total number of external routes exceeds the maximum limit. Check whether the asbr-summary command is configured to aggregate external routes.

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