Understanding and Demonstration: frame-relay inverse-arp)

Understanding and Demonstration: frame-relay inverse-arp)

Understanding and Demonstration: frame-relay inverse-arp)The teaching video corresponding to the configuration in: Lesson 9)

Frame-relay inverse-arp) This function is used to dynamically map L2 DLCI numbers to L3 addresses. In the previous chapter of this chapter, When configuring frame relay, we have repeatedly mentioned using the frame-relay map ip command to perform static ing, declaring that a local DLCI number is used to map to a specific remote connection, for how many remote terminals, You need to manually configure the number of DLCI numbers to statically map the commands of the remote IP address. In some complex frame relay network environments, a large amount of management overhead will be added, in addition, it cannot adapt to changes in the frame relay topology. The generation of reverse ARP for Frame Relay will solve these problems. In fact, the reverse ARP resolution of frame relay is very similar to the ARP Address Resolution Protocol in the LAN environment. ARP resolution in the LAN is to parse the target MAC address after knowing the target IP address; the reverse resolution of Frame Relay ARP is the layer-3 IP address mapped by the router to the local DLCI Number of the known layer-2 address.

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0046423251-0.png "title =" 5.png"/>

Step 1:As shown in figure 8.73, when the DTE device of the frame relay router is successfully connected to the DCE device of the frame relay switch, the LMS message is exchanged, A frame relay switch can declare that a new virtual circuit and the DLCI number corresponding to the circuit are available, but it cannot address the other end and cannot complete communication with the remote end.

Step 2:At this time, if the reverse ARP resolution mechanism of frame relay is enabled on Cisco's network device, it is enabled by default), router R1 will send a reverse ARP request data frame for Frame Relay, as shown in Figure 8.74; "I am router R1 and my IP address is 192.168.1.1. I am using the DLCI Number 102. Who are you?"

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0046425R1-1.png "title =" 6.png"/>

Step 3:When vror2 R2 receives a reverse arp request for frame relay, it will respond to this request and respond to the data frame, as shown in Figure 8.75, "I am R2, and the layer-3 IP address is 192.168.1.2 ." Then the router R1 associates the address with the local DLCI Number 102) to complete the dynamic ing of Frame Relay.

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0046421202-2.png "title =" 2.png"/>

Demonstration: difference between reverse ARP resolution and static ing of Frame Relay

Demonstration objectives:Difference between reverse ARP resolution dynamic ing) and static ing.

Demo environment:The demo environment is shown in Figure 8.73.

Demonstration Background:First, in the demo environment, the reverse ARP resolution of dynamic frame relay is used to complete communication, then the reverse ARP function of frame relay is disabled, and static ing is used to complete communication, finally, the differences between the two methods are compared using the show frame-relay map command.

Demo steps:

Step 1:For details about the configuration of the frame relay switch, we will not repeat the configuration of the frame relay switch here. Note: by default, the reverse ARP resolution frame-relay inverse-arp for frame frames is enabled on Cisco devices ), therefore, the router can use the reverse ARP function of frame relay to map the local DLCI number to the remote ip address. In this way, the frame-relay map ip command is no longer required for static ing, you only need to encapsulate the frame relay on the interfaces R1 and R2 of the router and configure the IP address. The specific configuration is as follows:

Frame Relay configuration of router R1:

R1 (config) # inte s1/0

R1 (config-if) # ip address 192.168.1.1 255.255.255.0

R1 (config-if) # encapsulation frame-relay

R1 (config-if) # no shutdown

Frame Relay configuration of vror2 R2:

R2 (config) # inte s1/0

R2 (config-if) # ip address 192.168.1.2 255.255.255.0

R2 (config-if) # encapsulation frame-relay

R2 (config-if) # no shutdown

Step 2:After completing the preceding configuration, You can ping the router R1 to the router R2. If everything works properly, you can see that the router R1 successfully pinged R2, and then run the showframe-relay map command on the router R1, to view the Frame Relay ing of router R1, as shown in Figure 8.76. dynamic indicates dynamic ing. 0x66 is actually a hexadecimal representation of DLCI 102, 0x1860 is the DLCI number in frame encapsulation. The value varies depending on the location of each bit in the frame. In fact, 0x66 and 0x1860 are actually used, they all represent the DLCI number, but the display method is different. The 0x1860 display mode includes the DLCI, the expanded Address EA, and the 16-bit address field of the congestion control bit.

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0046422N0-3.png "title =" 3.png"/>

Step 3: Disable the reverse ARP resolution function of frame relay inverse-arp on the device, and then use static ing to complete frame relay communication. The specific configuration is as follows:

The configuration of router R1 Using Frame Relay static ing:

R1 (config) # interface s1/0

R1 (config-if) # no frame-relayinverse-arp

R1 (config-if) # frame-relay map ip192.168.1.2 102 broadcast

R1 (config-if) # exit

The configuration of router R1 Using Frame Relay static ing:

R2 (config) # interface s1/0

R2 (config-if) # no frame-relay inverse-arp

R2 (config-if) # frame-relay map ip 192.168.1.1 201 broadcast

R2 (config-if) # exit

Step 4: After completing the preceding configuration, You can ping R2. if all the configurations are normal, R_1 can successfully communicate with R2, then run the showframe-relay map command on router R1 to view the Frame relay ing of router R1. As shown in Figure 8.77, static ing is used.

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/0046422935-4.png "title =" 4.png"/>

Note: If the remote router does not support reverse ARP resolution when reverse ARP resolution is used for Frame Relay, you can only use static ing of frame relay to complete the configuration, reverse ARP resolution is enabled on Cisco devices by default. However, when you have configured static ing for Frame Relay, reverse ARP resolution is automatically disabled!

This article is from the "unknown Christ" blog. For more information, contact the author!