Dynamic And Static Routing - Juniper J2300 User Manual

J-series™ Services Router User Guide
appropriately. Although it considers the entire path, the router at any individual hop
along the way is responsible only for transmitting the packet to the next hop in
the path. If the Phoenix router is managing its traffic in a particular way, it might
send the packet through Houston on its route to Miami. This scenario is likely if
specific customer traffic is treated as priority traffic and routed through a faster
or more direct route, while all other traffic is treated as nonpriority traffic.

Dynamic and Static Routing

Entries are imported into a router's routing table from dynamic routing protocols
or by manual inclusion as static routes. Dynamic routing protocols allow
routers to learn the network topology from the network. The routers within
the network send out routing information in the form of route advertisements.
These advertisements establish and communicate active destinations, which
are then shared with other routers in the network.
Although dynamic routing protocols are extremely useful, they have associated
costs. Because they use the network to advertise routes, dynamic routing protocols
consume bandwidth. Additionally, because they rely on the transmission
and receipt of route advertisements to build a routing table, dynamic routing
protocols create a delay (latency) between the time a router is powered on
and the time during which routes are imported into the routing table. Some
routes are therefore effectively unavailable until the routing table is completely
updated, when the router first comes online or when routes change within
the network (due to a host going offline, for example).
Static routing avoids the bandwidth cost and route import latency of dynamic
routing. Static routes are manually included in the routing table, and never change
unless you explicitly update them. Static routes are automatically imported into
the routing table when a router first comes online. Additionally, all traffic destined
for a static address is routed through the same router. This feature is particularly
useful for networks with customers whose traffic must always flow through the
same routers. Figure 56 shows a network that uses static routes.
Figure 56: Static Routing Example
Customer network
192.176.14.72
192.176.14.80
192.176.14.111
...
In Figure 56, the customer routes in the
These are hard links to specific customer hosts that never change. Because all
traffic destined for any of these routes is forwarded through router A, these routes
are included as static routes in router A's routing table. Router A then advertises
these routes to other hosts so that traffic can be routed to and from them.
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Routing Overview
A
Internet
192.176.14/24
subnetwork are static routes.