Overview of vro principles, Overview of vrouters

Overview of vro principles, Overview of vrouters

I. Principle Overview

Vro is one of the most common network devices. This article briefly describes its working principle:

1. Table: When the IP address is configured on the vro port, a direct connection route entry is automatically formed. Then, no matter Static Routing or dynamic routing protocol is used, route entries corresponding to each CIDR Block in the network must be generated in the routing table.

2. query table: analyze the destination IP address of the data packet and find the route table. If the corresponding route entry can be found, the data packet is forwarded on the corresponding port. If the corresponding route entry cannot be found, the data packet is discarded.

Note: In combination with my previous article "working principles of switches without VLAN configuration", we can see that the working principles of the switching network and the routing network are similar.

Ii. Case studies:

1. network topology:

For ease of understanding, we will explain the following in combination:

As shown in, host PC1 and PC2 Connect To routers R1 and R2 respectively. The gateway address of PC1 is 192.168.1.254, And the gateway address of PC2 is 192.168.3.254. Other configurations are shown in.

Now we can view the route tables of R1 and R2 (execute show ip route in privileged mode), as shown below:

It can be seen that there are only two direct connection CIDR blocks 192.168.1.0/24 and 192.168.2.0/24 in the R1 route table, while there are only two direct connection CIDR blocks 192.168.2.0/24 and 192.168.3.0/24 in the R2 route table.

At this time, ping the host PC2 from the PC1 host is not available, because R1 does not have a route of PC2 CIDR Block 192.168.3.0/24, and R2 does not have a route of PC1 CIDR Block 192.168.1.0/24.

The test results are as follows:

The result returned by the gateway 192.168.1.254 of PC1 is Destination host unreachable, indicating that the target host is inaccessible. When the ICMP packet sent by PC1 reaches R1, R1 checks its route table and does not find the route table corresponding to the CIDR Block of the destination address 192.168.3.0/24. Therefore, the data is discarded, A prompt message is returned to the source host PC1.

2. Table Creation

To connect PC1 and PC2 networks, we need to add route entries of PC2 and PC1 in the route tables of R1 and R2 respectively. This experiment is implemented through static routing. The command is as follows:

R1 (config) # ip route 192.168.3.0 255.255.255.0 192.168.2.2

R2 (config) # ip route 192.168.1.0 255.255.255.0 192.168.2.1

Now we can view the route tables of R1 and R2 (execute show ip route in privileged mode), as shown below:

We can see that a route entry of the "S" type is added (S-Static, which refers to Static Routing ).

3. query table

Ping the host PC2 from the PC1 host. The test result is as follows (the first two packets "timed out" are due to ARP execution. For details, refer to the working principle of ARP ):

When an ICMP packet arrives at R1 from PC1, R1 checks the destination IP address 192.168.3.1 of the packet, then, find the corresponding route entry "S 192.168.3.0/24 [1/0] via 192.168.2.2" in your route table and forward it from 192.168.2.2, then, let's look at the route entry "C 192.168.2.0/24 is directly connected, GigabitEthernet0/1", knowing that the data packet needs to be sent out from the port "GigabitEthernet0/1.

The packet sent from the "GigabitEthernet0/1" Port of R1 is received by the "GigabitEthernet0/1" Port of R2. R2 checks the destination IP address of the packet 192.168.3.1, then, find the corresponding route entry "C 192.168.3.0/24 is directly connected, GigabitEthernet0/0" in your route table ", therefore, the data packet is sent from the "GigabitEthernet0/0" Port of R2 to the target host pc2.

After receiving the ICMP packet, the target host PC2 finds that the target IP address is itself. Therefore, it constructs an ICMP response packet to change the target address to 192.168.1.1 and the source address to 192.168.3.1, after R2 and R1 return PC1 (the process of finding the route table of R2 and R1 is similar to the above), PC1 and PC2 can ping each other.

Iii. Summary

The above process shows that the working principle of a vro can be divided into two steps: "table" and "Table query", which are similar to that of a vswitch.