How does the S series switch receive the routing protocol message?

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When the S-series and E-series switches receive the protocol packets, the main control board (CPU) and the main control board (CPU) complete the related calculation and send the control message to update the routing information of the service board

Other related questions:
How does an S series switches process received routing protocol packets
Q: How does an S series switches process received routing packets? A: After receiving a routing protocol packet, an S series switches sends it to the MPU. After calculation, the MPU delivers control messages to an LPU for routing information updates.

S series switches routing protocol priority problem
default: - Direct�? - OSPF�?0 - IS-IS�?5 - Static�?0 - RIP�?00 - OSPF ASE�?50 - OSPF NSSA�?50 - IBGP�?55 - EBGP�?55

Configure OSPF to filter received routes on S series switches
The Open Shortest Path First (OSPF) is a routing protocol based on the link status. Unlike the routing protocols using the distance-vector (D-V) algorithm, OSPF ensures topology consistency and provides loop-free routes. To configure OSPF to filter routes, run the filter-policy import command. The record about the LSA of a route filtered out exists in the OSPF database. The OSPF process does not add the route to the routing table but the LSA of the route is advertised. That is, the peer end can receive the route. The filter-policy export command can only be used to configure OSPF to filter imported external routes to be advertised. OSPF also supports the filtering of routes carried in Type 3 LSAs on ABRs. This feature enables ABRs to filter routes when advertising Type 3 LSAs between OSPF areas. Only the packets with prefixes meeting requirements can be transmitted from one area to another. In this way, the incoming and outgoing packets of an area are controlled.

Routing protocol preference on S series switches
Preference of routing protocols Different routing protocols, including the static routing protocol may discover different routes to the same destination, but not all these routes are optimal. At a certain moment, only one routing protocol determines the preferred route to a certain destination. To select the optimal route, routes of these routing protocols including the static route are configured with preferences. When multiple sources of routing information exist, the route learned by the routing protocol with the highest preference (a smaller value indicates a higher preference) becomes the optimal route. The optimal route is then saved to the local routing table. Routers define the external preference and internal preference. External preferences are manually configured for routing protocols. The following lists the default external preferences of routing protocols: - Direct: 0 - OSPF: 10 - IS-IS: 15 - Static: 60 - RIP: 100 - OSPF ASE: 150 - OSPF NSSA: 150 - IBGP: 255 - EBGP: 255 Note: Value 0 indicates direct routes and value 255 indicates routes learned from unreliable sources. A smaller value indicates a higher preference. Except for direct routes, the priorities of routing protocols can be manually configured. In addition, the preference of each static route varies. Internal preferences of routing protocols cannot be manually configured. The following lists the internal preferences of routing protocols: - Direct: 0 - OSPF: 10 - IS-IS Level-1: 15 - IS-IS Level-2: 18 - Static: 60 - RIP: 100 - OSPF ASE: 150 - OSPF NSSA: 150 - IBGP: 200 - EBGP: 20 During route selection, a router first compares the external preferences of routes. When the same external preference is set for different routing protocols, the router selects the optimal route based on the internal preference. For example, two routes (an OSPF route and a static route) are available. Both routes can reach the destination 10.1.1.0/24, and the preferences of the two routes are set to 5. In this case, the router determines the optimal route according to the internal preferences. The internal preference (the value is 10) of OSPF is higher than that (the value is 60) of the static route. Therefore, the router selects the route discovered by OSPF as the optimal route.

How does OSPF filter received routes
As a link state-based routing protocol, OSPF is different from a distance-vector (D-V) algorithm routing protocol and ensures consistent topological relationship. This is an important condition for loop-free OSPF routing. You can run the filter-policy import command to filter routes in OSPF configuration. The link-state advertisement (LSA) of a route filtered out exists in the OSPF database. OSPF simply does not add the route to the routing table of the route manager. In addition, the LSA of the route is still advertised. That is, the neighbors still have this route. Note that the filter-policy export command can be used to filter routes when external routes are redistributed for advertisement. OSPF provides another feature: OSPF Area Border Router (ABR) Type 3 LSA filtering. This feature extends the ability of an ABR that is running the OSPF protocol to filter type 3 LSAs that are sent between different OSPF areas. This feature allows only packets with specified prefixes to be sent from one area to another area and restricts all packets with other prefixes. This type of area filtering can be applied out of a specific OSPF area, into a specific OSPF area, or into and out of the same OSPF areas at the same time.

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