The Routing Table Must Be Reviewed by Using the Command Show Ip Route
Routing and Switching grade the foundation of computer networks and the Internet in general. A network engineer must know routing principles similar the back of his/her hand!!
In this practical tutorial we will discuss the Cisco "show ip route" command which allows a network engineer to examine the routing table of a router device in a network.
The cadre functionality of Layer 3 in the OSI model (Network Layer) is to forwards (route) packets received on an interface of a routing device to the best destination.
Information technology is the router's job to select the best path that volition evangelize a packet to its destination as quickly and efficiently as possible.
This path selection process depends on the destination IP accost of the package received and the knowledge that the Router has almost reaching that destination.
Routing and Routing Tables
The "knowledge" that a Router has almost the fashion to accomplish destination networks is stored in the "Routing Table" of the device.
This Routing Tabular array contains all known destination networks, how they were learned and how to reach them (outgoing Interface).
The entire process of edifice this Routing Table relies on the information from neighboring routers (dynamic routes) or from statically configured entries by the network administrator (static routes).
This means when a network topology is created, there has to be some kind of configuration for the devices on that network to communicate with each other.
The two major options are dynamic routing and static routing – these are basically how routers learn about routes to destination networks.
Dynamic Routing
When dynamic routing is used, a routing protocol has to be configured on the Layer3 devices on the network, in order for them to share routing information.
Some popular routing protocols supported by Cisco routers include Routing Information Protocol (RIP), Open Shortest Path First Protocol (OSPF), Interior Gateway Routing Protocol (IGRP) and Extended Interior Gateway Routing Protocol (EIGRP), amid others.
When y'all opt for the implementation of dynamic routing, note that all routers on the network must be configured with 1 or more dynamic routing protocols.
If multiple routing protocols are used, then you accept to implement what is known as "road redistribution", which allows multiple routing protocols to work together and share routing information.
Although dynamic routing has the advantage of automatically updating the routing tabular array, it has a disadvantage of overusing router resources due to its nature of sending periodic updates. When dynamic routing is used, routing information is automatically learned and added to the routing table.
Static Routing
Static routing deals with the manual configuration of routes past the administrator. This means routing information is manually inserted into the routing tabular array.
This data includes things such as destination IP addresses, administrative distance or cost of getting to the destination network, and gateway IP to achieve the destination network.
The "prove ip route" control explained
One time a routing table is created i.eastward. there is convergence in the network, a logical topology is created from the physical network topology.
At this stage, routers on the network volition take all the necessary information to forrad packets they receive to the correct destination.
As a network administrator, information technology is important that you lot know how to verify this data. It is crucial that yous know how to check the routing table to encounter if y'all take all the routes needed for complete network communication to have place.
The "testify ip route" control is one of the most important commands related to routing on Cisco IOS devices in order to bear witness the routing tabular array of the router.
It gives you detailed information well-nigh the networks that are known to the router, either direct connected to the router, statically configured using static routing or automatically added to the routing table using dynamic routing protocols.
Let us take a look at the output from a show ip road command to sympathize how information technology works using the instance networks depicted beneath.
Nosotros have two example topologies beneath, 1 using RIP and another i using EIGRP so that to run into how the routing table looks in both cases:
Routing Table with RIP
The control was executed on router R2 shown in the figure below.
R2#show ip route
Codes:
C – connected, Southward – static, I – IGRP, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter expanse
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type two
E1 – OSPF external type 1, E2 – OSPF external blazon 2, Due east – EGP
i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, ia – IS-IS inter area
* – candidate default, U – per-user static route, o – ODR P – periodic downloaded static road Gateway of last resort is not set.
C 192.168.i.0/24 is straight connected, Serial0/0/0
C 192.168.2.0/24 is directly connected, Serial0/one/0
R 192.168.3.0/24 [120/1] via 192.168.1.1, 00:00:eighteen, Serial0/0/0
R 192.168.4.0/24 [120/2] via 192.168.ane.i, 00:00:xviii, Serial0/0/0
The C in the routing table output means that the networks listed are "straight continued". These represent the networks of the IP addresses configured on the physical (or virtual) interfaces of the device.
The R in the routing table shows destination networks learned via RIP dynamic routing protocol. If we were running OSPF, the entry would show O instead of R.
And so, Router R2 is learning almost the other networks via RIP routing protocol, which is depicted as R in the codes as we've said above.
For example, network 192.168.3.0/24 has been learned via 192.168.1.ane and can be reached via Serial0/0/0. This route has been added to the routing table by RIP.
As mentioned earlier, the routing table contains ALL the data about routes that are known to the router.
Administrative Distance
From the routing tabular array above, find the number [120/1] shown in the RIP road. This is the default Authoritative Distance of RIP which is 120.
Routing Table with EIGRP
In the following network topology the three routers implement EIGRP to dynamically distribute routing data between each other.
We will non examine how EIGRP is configured just let'due south discuss and explain the "prove ip route" output from each router:
R1#evidence ip route
Codes: C – connected, S – static, I – IGRP, R – RIP, Grand – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type one, N2 – OSPF NSSA external blazon two
E1 – OSPF external blazon one, E2 – OSPF external blazon 2, E – EGP
i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-ii, ia – IS-IS inter expanse
* – candidate default, U – per-user static road, o – ODR
P – periodic downloaded static road
Gateway of last resort is not fix
10.0.0.0/30 is subnetted, 2 subnets
C 10.10.ten.0 is direct connected, Serial0/0/0
D 10.10.10.4 [90/2172416] via x.10.10.2, 01:00:09, Serial0/0/0
C 192.168.10.0/24 is directly connected, FastEthernet0/0
D 192.168.20.0/24 [90/2172416] via 10.10.10.2, 01:00:09, Serial0/0/0
D 192.168.thirty.0/24 [90/2174976] via 10.10.ten.2, 01:00:09, Serial0/0/0
The routing table of Router R1 shows three networks learnt via EIGRP (denoted as D) and also 2 directly continued routes denoted as C.
For example, destination network 192.168.30.0 is learnt via EIGRP and can be reached via 10.10.10.2 from the Serial0/0/0 interface.
R2#testify ip route
Codes: C – connected, S – static, I – IGRP, R – RIP, G – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external blazon 2
E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP
i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, ia – IS-IS inter surface area
* – candidate default, U – per-user static road, o – ODR
P – periodic downloaded static route
Gateway of last resort is not set
ten.0.0.0/thirty is subnetted, 2 subnets
C 10.10.10.0 is direct connected, Serial0/0/0
C 10.x.ten.4 is directly connected, FastEthernet0/1
D 192.168.ten.0/24 [xc/2172416] via x.x.ten.ane, 01:05:eleven, Serial0/0/0
C 192.168.20.0/24 is directly continued, FastEthernet0/0
D 192.168.xxx.0/24 [90/30720] via 10.10.10.6, 01:12:53, FastEthernet0/1
The 2d router in the topology shows iii directly continued routes and two dynamic routes from EIGRP.
R3#show ip route
Codes: C – connected, South – static, I – IGRP, R – RIP, G – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type one, E2 – OSPF external blazon 2, E – EGP
i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-two, ia – IS-IS inter surface area
* – candidate default, U – per-user static route, o – ODR
P – periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/30 is subnetted, two subnets
D x.10.ten.0 [ninety/2172416] via x.10.x.5, 01:16:22, FastEthernet0/ane
C 10.10.10.4 is directly connected, FastEthernet0/1
D 192.168.10.0/24 [90/2174976] via 10.x.10.5, 01:16:22, FastEthernet0/ane
D 192.168.20.0/24 [ninety/30720] via 10.ten.10.5, 01:xv:xl, FastEthernet0/i
C 192.168.30.0/24 is straight connected, FastEthernet0/0
Authoritative Distance
The number [90/2172416] in the EIGRP routes above shows the default administrative distance of EIGRP which is xc and the metric value.
Other "Bear witness IP Route" command options
testify ip road [ip accost] : shows only information virtually the specified IP address.
prove ip route [ospf, rip, eigrp, etc] : shows only routing information learned from the specified routing protocol (e.one thousand bear witness ip road ospf).
evidence ip route static : displays information nigh statically configured routes.
show ip route continued : displays information about direct connected networks.
show ip route summary : shows summary data near ALL IP routes in the routing table.
Permit's see the above commands on the EIGRP network scenario shown above:
R1#show ip road eigrp
10.0.0.0/30 is subnetted, ii subnets
D x.x.10.4 [90/2172416] via x.x.ten.2, 01:19:53, Serial0/0/0
D 192.168.20.0/24 [90/2172416] via 10.10.x.2, 01:19:53, Serial0/0/0
D 192.168.thirty.0/24 [90/2174976] via ten.ten.ten.2, 01:19:53, Serial0/0/0
The to a higher place shows only routes learned by EIGRP.
R1#show ip route continued
C 10.10.ten.0/30 is directly connected, Serial0/0/0
C 192.168.ten.0/24 is directly connected, FastEthernet0/0
The above displays only directly continued routes.
R1#show ip route summary
IP routing table proper noun is Default-IP-Routing-Table(0)
IP routing table maximum-paths is 16
Route Source Networks Subnets Overhead Retentiveness (bytes)
connected 1 1 144 256
static 0 0 0 0
eigrp x 2 1 216 384
internal i 1148
Total 4 2 360 1788
The in a higher place displays a summary of all the routes and their source in the routing table.
R1#bear witness ip route 192.168.30.0
Routing entry for 192.168.30.0/24
Known via "eigrp ten", distance ninety, metric 2174976, blazon internal
Redistributing via eigrp 10
Last update from 10.10.x.ii on Serial0/0/0, 01:30:17 ago
Routing Descriptor Blocks:
* 10.ten.10.ii, from 10.10.x.two, 01:xxx:17 ago, via Serial0/0/0
Route metric is 2174976, traffic share count is one
Full delay is 20200 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops ii
If you insert a specific destination network in the control (for example 192.168.30.0 as shown to a higher place) then yous volition get all details about how this destination network is learned by the device. In our example to a higher place, network 192.168.30.0 is known via EIGRP process 10, from interface Serial0/0/0.
CCNA Heave
Chap half-dozen. IP Routing Routing Protocols
Source: https://xmccomplex.com.vn/view-routing-table/
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