Tuesday 6 November 2018

What is Stuck In Active (EIGRP)?

Stuck In Active (EIGRP)

The EIGRP convergence is the process when going active on a route is sometimes also by the name of the underlying algorithm, diffusing update algorithm (DUAL).

When a successor path is lost and there is no feasible successor is identified, the EIGRP router sends out queries on all interfaces in an attempt to identify an alternate path. EIGRP routers don’t select the successor until the EIGRP router receives a reply to all queries. When a router has received a reply for all its query messages, that router can safely use the best of the routes confirmed to be loop-free. The process can and does work well in many cases, often converging to a new route in less than 10 seconds.  If a reply is missing for 3 minutes, the router becomes stuck in active (SIA). In that case, it reset the neighbor's relationship with the neighbors that did not reply to queries.

EIGRP sends every query and reply message using RTP, so every message is acknowledged using the EIGRP ACK message.
To limit the scope of queries, there are two tools: stub routers and route summarization this us to reduce the work performed by the DUAL and the scope of query messages.


Stub routing is one way to limit queries. A stub router is one that is connected to more than two neighbors and should be a transit router. The EIGRP stub routing feature improves network stability, reduces resource utilization, and simplifies remote router (spoke) configuration. Stub routing is commonly used in a Hub-and-Spoke topology.

Here is the command:
R1(config-router)#EIGRP STUB?
  connected       Do advertise connected routes
  leak-map        Allow dynamic prefixes based on the leak-map
  receive-only    Set receive only neighbor
  redistributed   Do advertise redistributed routes
  static                 Do advertise static routes
  summary         Do advertise summary routes

·         Connected means the router advertises connected routes only for those interfaces that match with a network command.

·         Leak-map means the router advertises only which is specified by a leak-map

·         Receive-only means the router does not advertise any routes. This option can be used with any other option.

·         Redistribution means the router advertises only the redistributed routes.

·         Static means the router advertises only the static routes with redistributed static commands configured.

·         Summary means the router advertises only auto-summarized or statically configured summary routes

NOTE: By default, is connected and summary.

Before we start EIGRP configuration check out some important of EIGRP CCIE exam topics.

Here are the lists of all EIGRP labs and theories CCNA to CCIE

1.Enhanced Interior Gateway Routing Protocol (EIGRP)

2.Stuck In Active (EIGRP)

3.EIGRP Equal-Cost and Unequal-Cost load balancing

4.Route filtering passive interface

5.Route summarization

6.EIGRP STUB and Configuration

7.Routing Protocol Authentication (EIGRP ) and configuration







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