Differences between policy-based routing and default routing

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The operation object of policy-based routing is packets. Even if a routing table is available, packets are not forwarded according to the routing table, and they are forwarded based on a policy according to requirements.
According to the conventional routing and forwarding principle, packets are forwarded according to the destination addresses of the packets. Nowadays, more and more users expect that packets are forwarded and routed according to their defined policies on the basis of the conventional routing and forwarding. Policy-based routing enables the network administrator to formulate routing policies according to the source and destination addresses of packets, packet size, and link quality in order to change the forwarding paths of packets and meet user requirements.

Other related questions:
Priorities of policy-based routing and default routing for an AR router
Policy-based routing has a higher priority than default routing. If policy-based routing and default routing coexist, only policy-based routing takes effect. After policy-based routing loses effect, default routing takes effect.

How to configure OSPF to filter routes based on a routing policy
OSPF can use routing policies to filter routes. By default, OSPF does not filter routes. To configure OSPF to filter the routes to be received, run the filter-policy import command. To configure OSPF to filter the routes to be sent, run the filter-policy export command. You can use one of the following routing policies: 1. Basic ACL 2. Advanced ACL 3. IP prefix list 4. Route-policy

Matching sequence of policy-based routes
Policy-based routes are matched based on their node sequence numbers in ascending order.

What is the difference between sending default routes to a peer and controlling BGP route advertisement
The difference between the following functions is as follows: The implementation is different, but the configurations do not conflict. - After a BGP device is configured to send a default route to its peer, the BGP device sends a default route with the local address as the next hop address to its peer, regardless of whether there is a default route in the local routing table. This greatly reduces the number of routes on the network and lowers consumption of memory and network resources on the peer. Run the peer { group-name | ipv4-address | ipv6-address } default-route-advertise [ route-policyroute-policy-name ] [ conditional-route-match-all { ipv4-address1 { mask1 | mask-length1 } } &<1-4> | conditional-route-match-any { ipv4-address2 { mask2 | mask-length2 } } &<1-4> ] command to configure the AR to send the default route to the peer or peer group. - After control of BGP route advertisement is configured, you can configure the AR to advertise only routes that the AR wants to advertise or routes that the peer requires. The AR can be configured to control the BGP routes that are advertised globally or to a specified peer (group). - Run the filter-policy { acl-number | acl-nameacl-name | ip-prefixip-prefix-name } export [ protocol [ process-id ] ] command to configure the AR to control the BGP routes that are advertised globally. - Run the peer { group-name | ipv4-address | ipv6-address } filter-policy { acl-number | acl-nameacl-name | acl6-number | acl6-nameacl6-name } { import | export } command to configure the AR to control the BGP routes that are advertised to a specified peer (group).

Difference between a route and a gateway
A gateway is used to connect one network to another network. The gateway is an address. A route is a rule used to connect one network to another network. The route involves two basic actions: determine the optimal path and transfer information over a network.

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