>Can anyone explain to me exactly now static routes can save on
>overhead of the router. I know if you using a routing protocol that
>it keeps a routing table and updates are sent to the other routers,
>but when you use static routes I assume that it acts like a switch and
>just send the packets to where they need to go based on the static
>route....and it doesn't broadcast anything to the other routers. This
>is going to be used over a frame-relay network using subinterfacing
>(frame-relay interface-dlci xxx). My thought is that I can save a lot
>of overhead because the remote sites are just a small ethernet segment
>and none of the remote sites need to talk to each other.
Static routes can save both on router processing and on bandwidth.
When a router receives updates, it has to run an algorithm to determine
the best path and then place that route in the routing table (this
is an extremely simplistic description of what actually happens). The
algorithm may be a very simple one, such as what RIP uses, or very
complex, as in OSPF. The algorithm obviously translates into CPU
cycles, with more complex algorithms calling for more CPU. Static
routes do not require these algorithms-- *you* are the algorithm, telling
the router where to send packets.
Whether you use dynamic or static routes has no impact on performance
during actual routing-- the routing table lookup just looks for whatever
routes are in the table, regardless of how the route entries got there.
Where static routes *really* save, IMHO, is in bandwidth. RIP broadcasts
the routing table every 30 seconds, OSPF sends LSAs, etc. If there are
no decisions for a routing protocol to make, why use up some of your
bandwidth with what is essentially useless information?
For instance: Small frame relay networks are usually set up in a
hub-and-spoke topology. If one of those spokes dies, can the
router at the end of it find an alternate path back to the hub? If
not, what use is a routing protocol, other than to use up some percentage
of your expensive WAN bandwidth.
In such a topology, configure static routes in your hub router pointing
to each LAN on the spoke routers, via the frame relay interface addresses
of the spoke routers. On the spokes, add a single static default route:
IP ROUTE 0.0.0.0 0.0.0.0 A.B.C.D
where A.B.C.D is the frame relay interface of the hub router. Add
IP CLASSLESS to all routers, and you're in business. No muss, no fuss.
Customer Service Specialist
CCIE # 1919
Certified Cisco Systems Instructor
!nterprise Networking Services
US West Communications, Inc.
201 Third St. NW, Rm. 720
Albuquerque, NM 87102
Office: (505) 245-5857