Announcement of default routes in dynamic protocols (focusing on default-network)

 

Application of ip default-network in rip and ix2.

 

Purpose: advertise a vro that runs the corresponding dynamic routing protocol internally to create a dynamic default route

 

Only primary CIDR blocks can be set.

 

The default route created after the internal router uses the default route update message obtained by rip is in the 0.0.0.0 mode. Therefore, the VBR is set as the default main class CIDR block, we do not need to use the network to advertise, but it does not work in ergrip, because the internal router advertises that the default route entry created in this method is: only add the corresponding route * tag, therefore, the premise of successful creation is that you must learn such a route through the network, so you must use the network to advertise on the VBR, but the way to advertise is unrestricted, for example, if we use default to advertise 172.16.0.0, we can use 172.16.1.0 0.0.255 when using network. Note that the route table of the VBR must contain route entries such as 172.16.0.0 (whether rip or VPN) (if automatic or manual summary is enabled, subnet route entries can be used in the routing table. That is to say, if a default route entry takes effect internally, the update information sent to the route entry must contain the route entry of the primary network segment)

 

The next entry of the default route dynamically created on the internal router, from which device the update is obtained, and the next entry points to the corresponding interface of the device, which is easy to understand, because both Protocols belong to the distance vector type, the updated route entries

 

 

Note: in fact, we can use network 0.0.0.0 to advertise the created default route to the internal router, but this is a prerequisite, that is, when we manually create a default route on the VBR, the specified route entry cannot be the next one, but only the outbound interface. This is because the dynamic routing protocol can only advertise direct connections by default, in this way, the router can identify the default route as a direct connection route.

 

There are also two ways to advertise the default route in the dynamic routing protocol: default-information originate and redistribute. The two methods will be described in detail in future blogs, here is a simple summary:

 

We can use all methods except default-information originate for rip (v1 and v2) and OSPF;

 

However, ospf updates generally do not contain route entries such as 0.0.0.0. Therefore, we usually use default-information originate to implement

 

 

 

 

 

This article is from the "anti-walker" blog