Understand the Management Distance and measurement parameters in a vro

When talking about routing protocols and routers, administrative distance (administrative distance) and measurement (Metrics) are two important parameters. What do these two sets of parameters really mean? David Davis will introduce the two sets of parameters and explain the reasons why Cisco routers need to understand the importance of management parameters.

When it comes to the routing protocol and the channel used by the router, Management Distance and measurement are two important parameters. Full familiarity with these two sets of parameters plays an important role in understanding network performance, reliability, and loop selection.

If you are not familiar with management spacing and metrics, you will not pay attention to them even if you see these parameters. If you enter the show ip route command, you will notice that the two parameters appear in the ARC behind the router. Here is an example:

O 10.1.103.0/24 [110/791] via 10.1.100.2, 00:39:44, Serial1/0. 21

In this example, 110 indicates the management spacing, and 791 indicates the measurement. By entering the same show ip route command and specifying the router mode, you can see more detailed information. This is an example:

Router # show ip route 10.1.103.0
Routing entry for 10.1.103.0/24
Known via "ospf 100", distance 110, metric 791, type intra area
Last update from 10.1.100.2 on Serial1/01:09:25. 21, ago
Routing Descriptor Blocks:
* 10.1.100.2, from 172.16.1.1, 01:09:25 ago, via Serial1/. 21
Route metric is 791, traffic share count is 1

But what do these numbers really mean? Let's take a closer look at the meaning of each parameter.

Management Interval
Management spacing (AD) determines which channel the router chooses when it faces two channels of the same source. That is, if the router receives information from different sources but with the same content, which channel the router trusts. A better way is to make the best effort to select local information, and the global information is somewhat repetitive, so local information is more trustworthy.

If your router only has one routing protocol and one WAN loop, or if you only use static routing, the management distance will not affect you. However, this does not mean that you do not need to understand the role of management spacing.

However, if you have a complicated network system, such as two WAN circuits, or you use two routing protocols (even if one of them is a static route ), you should understand the importance of management spacing.

Routing resources are not justRIPSome routing protocols such as OSPF or BGP, and some resources (such as the router interface) and Static Routing (the router you use as the Management Server) connected to the vro ).

The router selects the trusted Resource Based on the Management interval. The smaller the management interval, the more trustworthy its routing resources are.

To facilitate this decision, the router has installed a pre-program schedule table displayed in all possible resources and the default Management gap. Table A provides an example of this table. (Although the distance command in vro configuration mode is used to change the manager's default Management spacing, this is usually an undesirable method .)

SOURCE OF THE ROUTE                              DEFAULT DISTANCEConnected Interface or static route to an Interface   0Static route to an IP Address                      1EIGRP Summary      5BGP External      20EIGRP Internal      90IGRP      100OSPF      110IS-IS      115RIP      120EIGRP External      170BGP Internal      200Unknown Source      255

For example, if the router receives a route entry from OSPF and a route entry fromRIPIt will select the OSPF route. Because the OSPF management interval is 110RIPThe management interval of is 120.

Here is another example: for example, if your vro receives a route from Internal, its management interval is 90, But you accidentally input a static route to an IP address, the Gap Management address of this IP address is 1. The vroeigrp uses a static route instead of an IPsec route.

The last point is to emphasize that the management interval is the focus of the CCNA examination. If you are preparing to take this test, you must know the Management Distance of the general routing protocol.

Measure
The routing protocol uses metrics to determine which route table to be placed when two valid routes can be sent to the same target file. The router puts the route table in the route table with the smallest measurement, because it considers this route as the nearest and therefore the best.

In contrast to the management distance, the measurement has only one routing protocol. They cannot process routes in multiple resource pools.

For example, enter the show ip:

P 10.55.103.0/24, 1 successors, FD is 6049536
Via 10.220.100.1 (6049536/5537536), seri_3/0
Via 10.55.100.14 (52825600/281600), Tunnel55

Note that there are two routes transmitted to this network in this network. However, this router only accepts one of the routes with the shortest measurement in the routing table. Here is an example of a route table entry:

Router # show ip route 10.55.103.0
Routing entry for 10.55.103.0/24
Known via "Kerberos 100", distance 120, metric 6049536, type internal
Redistributing via image100
Last update from 10.220.100.1 on seri_3/0, 00:56:12 ago
Routing Descriptor Blocks:
* 10.220.100.1, from 10.220.100.1, 00:56:12 ago, via seri_3/0
Route metric is 6049536, traffic share count is 1
Total delay is 41000 microseconds, minimum bandwidth is 512 Kbit
Reliability 226/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2

Different routing protocols have different algorithms for metrics.RIPThe OSPF algorithm is based on the number of hops, while the OSPF algorithm is based on the bandwidth, which is determined by the bandwidth, delay time, load, and reliability.

Article entry: csh responsible editor: csh