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Chapter 2
The Thomson Gateway FIB entries
2
The Thomson Gateway FIB entries
Introduction
The most important function of the forwarding process is to find an output port for a given destination IP. As
mentioned before, the relation between a set of similar destinations and an output port is defined in the
forwarding table. Question is, how do entries (routes) end-up in there?
This section gives an overview of the three different routes that are supported and used in the Thomson
Gateway:
>
Dynamic routes
>
Static routes
>
Semi-static routes
Definitions
When turning on the Thomson Gateway with default configuration but not connected to any link, only
routes
can be found in the routing table.
All other routes added afterwards are
dynamic routes only originate from routing protocols.
This is why there is a third category called the
originated through:
>
Dynamic Host Configuration Protocol (DHCP)
DHCP is client-server based. The DHCP client asks for a route and the DHCP server gives one. The route
exists until the lease expires.
>
Point-to-point protocol (PPP)
The route is automatically added when the PPP session is established and automatically removed when
the PPP session goes down.
Illustration
The picture below shows all possible routes that are supported by the Thomson Gateway:
The RIB gathers all the routes coming from the routing protocols and then forwards the routes with the
lowest metric to the FIB. Only the static and semi-dynamic routes will be explained in this configuration
guide.
E-DOC-CTC-20051017-0168 v1.0
dynamic
routes. This is not in line with the general accepted fact that
semi-dynamic
routes. To this category belong routes
Dynamic Routes
RIP
OSPF
BGP
Static Routes
Standard
Interface
Extended
Semi-dynamic Routes
PPP
DHCP
RIB
FIB
static
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