Understanding management spacing and measurement parameters in routers

When it comes to routing protocols and routers, management spacing (administrative distance) and metrics (Metrics) are two important sets of parameters. What do these two sets of arguments really mean? David Davis will introduce you to these two sets of parameters and explain why you need to understand the importance of management parameters using a Cisco router.

When it comes to routing protocols and which channel the router uses, management spacing and metrics are two important sets of parameters. Fully familiar with these two sets of parameters to understand the network performance, reliability and circuit selection and other parts of the very important role.

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

O 10.1.103.0/24 [110/791] via 10.1.100.2, 00:39:44, Serial1/0:0.21

In this example, 110 represents the management spacing and 791 represents the metric. You can see more detailed information by entering the same show ip route command and specifying the router, which has 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 Serial1/0:0.21, 01:09:25 ago
Routing Descriptor Blocks:
* 10.1.100.2, from 172.16.1.1, 01:09:25 ago, via Serial1/0:0.21
Route metric is 791, traffic share count is 1

But what do these numbers really mean? Let's look at the meaning of each parameter in detail.

Manage Spacing

Management spacing (AD) is the choice of which channel the router will choose when facing two identical channels from different sources. In other words, if the router receives information from different sources but with the same content, the router trusts which channel. A better approach is that local information is more trustworthy because of the effort to select local information and how much of the global information is somewhat repetitive.

If your router has only one routing protocol and one WAN loop, or if you only use static routing, the management spacing will not affect you. But that doesn't mean you don't need to understand the role of management spacing.

But if you have a complex network system, such as two WAN loops, or if you use two routing protocols (even if one of them is static), you should be aware of the importance of managing spacing.

Routing resources are not just some routing protocols such as RIP, OSPF, or BGP, but there may also be resources connected to the router (such as the router's interface) and static routes (the routers you use as the Management Server).

Routers choose which resources to trust based on administrative spacing. The smaller the management spacing, the more trustworthy it is to route resources.

To facilitate this decision, the router installs a scheduler schedule that is displayed in all possible resources and by default management spacing. Table A provides a demonstration of this form. (Although the manager changes the default management spacing by using the distance command in router configuration mode, this is often an undesirable method.) ）

For example, if the router receives a route from OSPF and a route from RIP, it chooses the OSPF route. Because the management spacing of OSPF is 110, the management spacing of RIP is 120.

Here's another example: your router receives a route from EIGRP internal, and its management spacing is 90, but you accidentally enter a static route into an IP address where the spacing management address is 1. Then the router uses a static route and does not use EIGRP routing. (☆ Introduction to Programming Network ☆)

Finally, it is emphasized that management spacing is the focus of CCNA examination. If you are going to take this exam, be sure to know the management spacing of general routing protocols.

Measure

The routing protocol uses metrics to determine which route the routing table is placed in when there are two valid routes that can be sent to the same destination file. The router puts the routing table in the least-measured route because it considers the route to be the most recent and therefore the best.

As opposed to management spacing, metrics have only one routing protocol. They cannot process routes in multiple resource pools.

For example: Enter a show ip eigrp topology command:

P 10.55.103.0/24, 1 successors, FD is 6049536
via 10.220.100.1 (6049536/5537536), Serial3/0
via 10.55.100.14 (52825600/281600), Tunnel55

Note that this EIGRP routing protocol has two routes routed to this network. However, this router accepts only one of the shortest routes in the routing table. Here is an example of a routing table entry:

Router# show ip route 10.55.103.0
Routing entry for 10.55.103.0/24
Known via "eigrp 100", distance 120, metric 6049536, type internal
Redistributing via eigrp 100
Last update from 10.220.100.1 on Serial3/0, 00:56:12 ago
Routing Descriptor Blocks:
* 10.220.100.1, from 10.220.100.1, 00:56:12 ago, via Serial3/0
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. The RIP algorithm is based on the hop count, OSPF is based on bandwidth, and the EIGRP is based on bandwidth, latency, load, and reliability.

David Davis has been engaged in it for 12 years and has received a series of certificates including Ccie,mcse+i, CISSP, CCNA, CCDA and CCNP. He currently holds a system/network administrator position in a private retail company and is a part-time advisor to the network system.