Requirements for Deploying VLSM
The successful deployment of VLSM has three prerequisites:
  The routing protocols must carry extended network prefix informa 
tion with each route advertisement.
  All routers must implement a consistent forwarding algorithm based
on the  longest match. 
  For route aggregation to occur, addresses must be assigned so that
they have topological significance. 
Routing Protocols Must Carry Extended Network Prefix Lengths
Routing protocols, such as OSPF and I IS IS, enable the deployment of
VLSM by providing the extended network prefix length or mask value
along with each route advertisement. This permits each subnetwork to
be advertised with its corresponding prefix length or mask. If the rout 
ing protocols did not carry prefix information, a router would have to
either assume that the locally configured prefix length should be
applied, or perform a look up in a statically configured prefix table that
contains all of the required masking information. The first alternative
cannot guarantee that the correct prefix is applied, and static tables do
not scale since they are difficult to maintain and subject to human error. 
To deploy VLSM in a complex topology, the administrator must select
OSPF or I IS IS as the Interior Gateway Protocol (IGP) rather than RIP 1.
Note that RIP 2, defined in RFC 1388, improves the RIP protocol by
allowing it to carry extended network prefix information. Therefore,
RIP 2 supports the deployment of VLSM. 
Forwarding Algorithm Based on the Longest Match
All routers must implement a consistent forwarding algorithm based on
the longest match algorithm. The deployment of VLSM means that the
set of networks associated with extended network prefixes may mani 
fest a subset relationship. A route with a longer extended network pre 
fix describes a smaller set of destinations than the same route with a
shorter extended network prefix. As a result, a route with a longer
extended network prefix is more specific while a route with a shorter
extended network prefix is less specific. Routers must use the route
with the longest matching extended network prefix (most specific
matching route) when forwarding traffic. 
U N D E R S TA N D I N G   I P   A D D R E S S I N G
2 4






footer




 

 

 

 

 Home | About Us | Network | Services | Support | FAQ | Control Panel | Order Online | Sitemap | Contact

reliable web hosting

 

Our web partners: Inexpensive Web Hosting Jsp Web Hosting Jsp Web Hosting Cheapest Web Hosting  Java Web Hosting

 Quality Web Templates Dreamweaver Web Templates Frontpage Web Templates

Jsp Web Hosting Cheapest Hosting Cheapest Web Hosting Java Web Hosting Tomcat Web Hosting

Quality Web Hosting Best Web Hosting Java Web Hosting

Visionwebhosting.net Business web hosting division of Vision Web Hosting Inc.. All rights reserved