Tuesday, 6 November 2018

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, EIGRP router sends out the 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 is 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 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 EIGRP ACK message.
To limit the scope of queries, there is two tools we use stub routers and route summarization this us to reduce the work performed by the DUAL and the scope of queries messages.

EIGRP STUB

Stub routing is one way to limit queries. A stub router is one that is connected to on more than two neighbors and should be a transit router. The EIGRP stub routing feature improve 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 advertise connected routes only for those interfaces which matched with a network command.

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

·         Receive-only means the router do not advertise any routes. And this option can be used with any other option.

·         Redistribution means the router advertise only the redistributed routes.

·         Static means the router advertise only the static routes with redistributed static command configured.

·         Summary means the router advertise 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 is 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





No comments:

PIM Sparse Mode

PIM Sparse Mode  ( PIM-SM )  PIM  Sparse Mode explicitly builds unidirectional shared trees rooted at a ( RP ) rendezvous point per...