What is the difference between sending default routes to a peer and controlling BGP route advertisement

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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).

Other related questions:
Differences between policy-based routing and default routing
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.

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.

Differences between static and dynamic routes
The differences between static and dynamic routes are as follows: Static routes are easy to configure, have low requirements on the system, and apply to simple, stable, and small networks. The disadvantage of static routes is that they cannot automatically adapt to network topology changes. Therefore, static routes require subsequent maintenance. Dynamic routing protocols have their routing algorithms. Therefore, dynamic routes can automatically adapt to network topology changes and apply to the networks on which Layer 3 devices are deployed. The configurations of dynamic routes are complex. Dynamic routes have higher requirements on the system than static ones and consume network resources and system resources.

Configuring OSPF to import default routes on the USG2000 series
Configure OSPF to import default routes on the USG2000 series as follows: 1. In the user view, run the system-view command to enter the system view. 2. Run the ospf [ process-id ] command to access the OSPF view. 3. Select the following configurations as required. To import a default route to the OSPF process, run the default-route-advertise [ [ always | permit ] | cost cost | type type | route-policy route-policy-name ] * command. To specify the default cost of Type-3 summary LSA, run the default-route-advertise summary cost cost command.

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