Can anyone explain me what is the difference between distance vector protocol and path vector protocol.
Why we are calling BGP as Path vector protocol .
In Best path selection we use the AS_path length as 4th parameter ..
This is not a silly question ... I google it never find the exact answer ...
BGP's path vector routing information includes the 'path' of ASes that are used to reach the destination, BGP has a complex path selection process. AS-path length has nothing to do with the number and or speed of the links to reach the destination and so an AS-path length of 2 can take far more time than an AS-path length of 4 because you don't know the inside topology of those ASes.
Distance vector will give you the actual number of link hops (RIP) or a metric of hops, and link speed (a simplified description of EIGRP). Distance vector does not give you information of what links you will use (the path you will take) BGP does tell you what ASes you will transit.
Difference b/w Path vector and Distance vector . . . BGP is using the Path-vector Protocol means that BGP using the valid and Best path selection . BGP select the best path and the valid path . In the whole process bgp wants to readability to its destination . BGP see the whole path from source to destination . And this the one of reason that BGP is the slowest convergence time protocol in all protocols . On other hand Distance vector protocol is simply follow the next-hop . It (Distance vector ) do not care of the whole path from Source to Destination . It only think about the next hop and dont care about the whole best path .
Thanks
As per my opinion distance vector protocol is named as such because it contains the information of the exact distance and where exactly it needs to head to reach the destination. The 2 major quality of a distance vector protocol is that it will send the updates periodically and it's update would contain information only about directly connected neighbors whereas link state protocol sends information of all the known routes and does send it non-periodically (triggered update).
On the other hand BGP is said to be a path vector protocol because first it has many attributes by which path selection criteria can be tuned, even if we consider default metric which is AS path attribute, it doesn't know how the other AS is going to route the traffic (remember the Golden Rule of BGP) i.e., it is unaware that how many other routers/hops it needs to pass by. Secondly routes learned from other neighbors are never passed on unless validated by IGP (Rule of synchronization) differentiating it from link state routing protocol. BGP however does send triggered updates. Even neighbors need to manually configured unlike any distance vector or link state routing protocols.
The DVR protocol is an intra-domain routing protocol, that is, a protocol used inside a domain (by its hosts and routers).
DVR is a type of protocol, where routers send regularly a Distance Vector (DV) to all its interfaces. The DV is basically an array (vector) that indicates the distance towards each known destination.
An example of a DVR protocol is the Routing Information Protocol (RIP).
The PVR protocol is an inter-domain routing protocol, that is, a protocol used between domains.
PVR is also a type of protocol, where domains send _Path Vectors (PV) to each other. A PV is basically an array which contains the inter-domain path to a domain.
An example of a PVR protocol is the Border Gateway Protocol (BGP). The BGP inter-domain path is also known as the AS path. AS stands for Autonomous System: it is basically a number that uniquely identifies a domain.
For more information I recommend the following documents:
