Layer 3

EIGRP Updates Breakdown

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So, in order for the global routing table to have EIGRP routes in it, EIGRP has to first be enabled, then go through a process through with it determines which routes are Feasible successors (Best routes) and only then install them to the global routing table.

EIGRP has five basic messages it uses for this EIGRP collaboration between its neighbors.

  • Hello
  • Update
  • Query
  • Reply
  • ACK

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EIGRP Basics (Passive Interfaces)

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When EIGRP is up and operational, unicast and multicast EIGRP packets or constantly flooding the network to make sure EIGRP routes are up and are using the best path. These packets are important but not always necessary. There are situations when disabling an interfaces ability to spam the network with EIGRP packets is appropriate and will still allow for a fully operational EIGRP convergence. The way to achieve this is by configuring an interface to passive mode. EIGRP will still advertise the network/subnet configured on that interface, however, the interface will not participate in sending or processing of EIGPR packets.

Here is an example:

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CCNP Routing & Switching ROUTE 300-101 Chapters 1 & 2 Notes Part I

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CCNP Routing & Switching ROUTE 300-101 Chapters 1 & 2 Notes:

  • There is a natural need for routing protocols
    • The use of layer 3 devices
    • Scalability
      • The most common routing protocols used in an enterprise/campus networks are versions or RIP, EIGPR, OSPF
      •  Most common routing protocol used for external/untrust (Internet) networks is BGP
    • There are 3 Routing Protocol Categories
      • Distance Vector (Sends full copy of the routing table at certain interval)
        • Distance-Vectore routing protocols use one of the following approaches to prevent routing loops:
          • Split Horizon – This is when an interface is prevented to advertise a route which it already learned on that interface. 
          • Poison Reverse – This is when an interface receives a route advertisement but then re-advertises the same route out with a metric considered infinite.

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PING

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PING is one of the most used tools in networking, there are two main uses for the “ping” tool:

1. Troubleshooting: Ping is used to confirm whether or not you are able to reach a particular layer 3 device. It also give you the round trip time between to end points to confirm the reliability of a circuits path.

2. Monitoring: Ping is used to monitor links/interfaces to make sure a circuit is up.