Flooding protocol in shortest path fast algorithm (link state algo)

Replies

• 

  durga ch

  Dynamic Routing protocols can be of three types
  1. Distance vector protocols
  2. Link state protocols
  3. Hybrid protocols
  
  now , each protocol has its own metric parameters on which they forward packets. Like for DVP -its the hop count , for LSP its the cost and so on and so forth.
  When you consider the SPF algorithm, the shortest path in sense the path with least cost. The metrics for cost can include bandwidth, round trip time etc. its a better way of routing that the native distance vector . Consider the standard example of 2 routes available between 2 routers. Route 1- is least hop but worst in BW and Route 2 is better in BW and with a little more hops to traverse. SPF algo makes sure the bandwidth part is considered rather than just hop count.
  The protocol implements so called Dijikstra algorithm ( shortest path first algorithm).Please refer to the below link
  
  
  #-Link-Snipped-#
• 

  king99

  hi thanks for the link it helped me a lot , Suppose there is case L1----r1-----L2 ( these are connected by router 1 ) if further it happens that there is link failure and as a result L1 gets disconnected from r1 but still remains connected to L2 then in this scenario how can we define and explain "Count to infinity problem " both in link state and distance vector algorithm ??
• 

  durga ch

  if L1 connects to L2 only through R1, and if R1 goes down , how is it possible that L1 is still connected?
  count to infinity problem is different than what you are mentioning here.
  let me try explaining it.
  
  consider L1 <-->R1 <--> R2 <-->L2
  
  before a routing protocol is run the routing tables of R1 and R2 are as below
  
  R1
  L1 -- interface ethernet 0
  R2 -
  
  for R2,
  L2 -- interface ethernet 0
  R1 -- interface serial 0- inerface serial 0
  
  
  
  hence both R1 and R2 are aware of only directly connected networks and not the ones connected to the other router
  
  when a routing protocol is enabled on R1 and R2 ( be it disance vector or link state) the routing tables now show
  
  R1
  L1 -- interface ethernet 0
  R2 - inerface serial 0
  L2 via R2 (cost/ hop count)
  
  for R2,
  L2 -- interface ethernet 0
  R1 -- interface serial 0
  L1 via R1 (cost/hop count)
  
  now say L1 goes down.hence R1 is no longer directly connected to L1.
  In the next routing update, R2 sends to R1 , it mentions that it has connection to L1 ( via R1) and thus misleading R1 to think that there is another link to L1. these updates keep going around, even when there is no real link.
  
  is this explaination ok?
• 

  king99

  Thanks for reply but as mentioned above regarding routing table entries L1-interface Ethernet 0 also R1- interface serial 0( what it says exactly does it also stores IP of the next machine ?? ) what is difference in Interface serial and Ethernet serial , please can you elaborate on it ??
• 

  durga ch

  interface ethernet/fastethernet/gigaethernet corresponds to LAV cable ( the rj 45 pin cable what you generally connect to your computer)
  the seral interface uses a serial cable, like the db 16 pin .
  Routers are generally conected with serial cables . the reason being, they give us the flexibility to set clock rate at each end thus helping in syncronisation.