In-depth analysis of the IGRP Routing Protocol

As for the routing protocol, we all know that the RIP routing protocol is the earliest version. With the complexity of the network structure and the increasing standards of enterprises. The RIP Protocol has gradually withdrawn from the historical stage. Then we propose the IGRP routing protocol. Unlike the RIP Protocol, the IGRP routing protocol uses port number 9 on the IP layer for Packet Exchange (RIP uses port 520 and UDP)

IGRP uses the concept of autonomous system AutonomousSystem. The autonomous system can be defined as a route selection domain RoutingDomain) or a process domain processDomain ). The Autonomous System of the IGRP routing protocol is a process domain-a group of routers that use the IGRP routing protocol as the common routing selection protocol. By defining and tracking multiple Autonomous Systems, the IGRP routing protocol allows multiple process domains to run in one IGP environment. In this way, communication within one domain can be isolated from that in another domain. Inter-Domain traffic can be re-allocated through routes )! For the definition of these numbers, for example, in the AS10igrp10igrp30IGRP routing protocol, two autonomous system numbers 10 and 30 are the two process domains of IGRP. Here, process domains 10 and 30 communicate with each other through a router connected to the two process domains. AS10 indicates the route selection domain. In the IGRP update message, the IGRP Routing Protocol divides route entries into three categories: Internal route InteriorRoute, system route SystemRoute), and external route exteriorRoute ), each IGRP route entry belongs to one of the three categories.

Internal route -------- refers to the path to reach the subnet address of a master network, where the master network refers to the master network address of the data link that is broadcasting the update of this route. In other words, the subnet advertised as an internal route is "local" for the primary network that notifies the router and the receiving router to be connected together.

System route --------- refers to the path to the network address summarized on the network border router.

External route --------- is the path to the ultnetwork marked as the default network. For the default network, the router will directly send all data packets without matching the specific destination network. For example, because the image cannot be sent up, It is omitted ......

IGRP route protocol timer and Stability

The update period of the igrp routing protocol is 90 S. To prevent the synchronization of the update timer, the IGRP routing protocol removes a random jitter variable up to 20% for each update time. Therefore, the time required for each update cycle is between 72 and 72 ~ Change between 90 s. When a route is learned for the first time, the invalid timer of the route is set to 270 s, which is three times the update cycle time. At the same time, the refresh timer is set to 630 s, that is, 7 times the update cycle time. Each time the router receives an update message for this route, these timers will be reinitialized. If the timer for an invalid timer times out before receiving an update message, the route is marked as inaccessible. However, before the router refresh timer times out, this route will be retained in the route selection table and advertised as an inaccessible route. If the refresh timer times out, this route will be deleted from the route selection table.

Repeat the RIP timer. The RIP route update timer is 30 seconds. The router is invalid. The timer is 90 seconds. The timer is refreshed. the Rip Protocol running in Cisco IOS also has a timeout timer, the default value is 180 s. If a route update is not received within s (six update cycles), the number of hops of the route will change to 16, that is, mark it as an inaccessible route. If the destination address of a route changes to inaccessible, or the next hop router increases the measurement to reach the destination address, causing an update trigger, this route enters the suppression time state of an update cycle of S3 times plus 10 s. New information about the destination address is not accepted by the router until the suppression timer times out. The nometricholddown command can be used to disable the suppression feature of the IGRP routing protocol. In a network topology without a routing loop, the suppression feature has no practical significance, disabling this feature will help reduce the convergence time of the IGRP routing protocol. The default timer can be changed using the following command:

Timersbasicupdateinvalidholddownflush [sleeptime] Except for the sleeptime option, this command was used to change the timer of the RIP Protocol. Sleeptime is a periodic millisecond-level timer. When an update is triggered, Sleeptime is used to delay a normal route update. The default value of the timer should be changed only after the obvious problem occurs in the network and the consequences of changing the timer are carefully considered.

Measurement of IGRP Routing Protocol

By default, the IGRP routing protocol uses the link bandwidth and latency of the routing protocol as the measurement value. Two other features of the link-load and reliability can only be applied after manual configuration on the router. You can use the showinterface command to observe the value of the composite metric for the IGRP routing protocol on a specific interface.

Bandwidth ------ the Bandwidth is expressed in Kbit/s units. When calculating the measurement value of a link, it is only used as a static value and does not need to reflect the actual Bandwidth used by the link, that is to say, bandwidth does not need to be measured dynamically. For example, the default bandwidth of a serial interface is 1544 Kbit/s, regardless of whether the link connected to the serial interface is T1 or 56K. The default bandwidth value can be changed using the bandwidth command. The update packet of the IGRP routing protocol uses three 8-bit bytes to represent the IGRP "Bandwidth ". Bwirp is used to indicate that it is obtained by dividing the 7th Power of factor 10 by the bandwidth. Therefore, if the bandwidth of the interface is 1544, bwirp = 107/1544 = 6476 or 0x00194C

Latency (delay) ----- latency, like bandwidth, is also a measurement value of static features, and does not need to be measured dynamically. latency can be expressed by the DLY parameter displayed by the showinterface command, the Unit is (microsecond) the default latency of an interface can be changed through delay, and 10 microseconds is used as the minimum unit of measurement for command configuration. DLYigrp = DLY/10IGRP identifies an inaccessible route path by setting DLYigrp = 0xFFFFFF. This value is about 167.8 s. Therefore, the maximum latency of an IGRP route end is 167 s.

Reliability (Reliability) ------ Reliability is a dynamic measurement parameter. It is expressed by an 8-bit number. 255 represents a 100% reliable link, and 1 represents the lowest reliable link. Run showinterface.