Thursday, 1 September 2016

EIGRP - Part 6

EIGRP Update Messages

       EIGRP use update message between EIGRP router for adjacency. It use RTP (Reliable Transport Protocol)  and its function to deliver EIGRP update packet between neighbors in a reliable and ordered way. EIGRP send multicast and unicast packet just keep think your mind they all packet are sent reliable. Reliable means that when we send a packet we want to get an acknowledgment from the other side to make sure that they received it.

EIGRP also use following update message

   1.) Hello message
               EIGRP sends Hello packets once it enabled on a router for a particular network. Hello message use to identify neighbor. EIGRP Hello packet sends on local link using multicast address . 

   2.) Update message
               When EIGRP establishment first adjacency with neighbors than it send full topology information only one time. After than if any changes is happen in network than it send update message which have only changes network.

    3.) Query message
               EIGRP query message are multicast and are used to reliably request routing information. EIGRP query packet are sent to neighbor when a route is not available and the router need to ask about the status of route for fast convergence.

   4.) Reply message
              EIGRP Reply packets are sent in response to query packet.

  5.) Ack message
              An  acknowledgment packet is simply EIGRP hello packet that contains no data. Ack packets are used by EIGRP to confirm reliable delivery of EIGRP packet.

   As per topology changes EIGRP use  main two  message: update and AcK
Update message is contain updated information of topology and ACK is receipt of the update packet. 
       Update packet contain following information:

        1.) Prefix
        2.) Prefix length
        3.) Metric component: Bandwidth, delay, reliability, load, MTU and hope count.

EIGRP Feasible Distance and Reported Distance 

 Feasible Distance (FD)
           Integer metric for the route, from the local router's perspective, used to the local router to choose the best route for that prefix.

Reported Distance (RD)
          Integer metric for the route, from the neighboring router's perspective. Used by the local router when converging to a new route. It also known as Administrative Distance.

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