3Com 10014299 manual Typical Sub-Interface Configuration Example

228CHAPTER 16: CONFIGURING LAPB AND X.25

[Router-Ethernet0]ip address 196.25.231.1 255.255.255.0

[Router-Ethernet0]interface serial 0[Router-Serial0]ip address

192.149.13.2 255.255.255.0

[Router-Serial0]link-protocol x25

[Router-Serial0]x25 x121-address 1004358902

[Router-Serial0]x25 vc-range bi-channel 8 1024

[Router-Serial0]x25 pvc 4 ip 192.149.13.1 x121-address 1004358901 broadcast packet-size 512 512 window-size 5 5 [Router-Serial0]quit

[Router]rip

In above configuration, the permanent virtual circuit numbers of routers A and B are different: 3 and 4 respectively. Virtual circuit refers to the end-to-end logical link between the calling DTE and the called DTE, while logical channel refers to the logical link between two directly connected devices (either between DTE and DCE, or between the ports of two packet switching exchanges). A virtual circuit consists of several logical channels, and each logical channel has a separate number. The virtual circuit between routers A and B is shown in (suppose this virtual circuit passes four packet switching exchanges in the network).

Figure 71 A virtual circuit consisting of several logical channels

	LC 3
RouterA		PBX
	PBX
		LC 3	LC 4
	LC 243
		PBX	RouterB
	PBX	LC 24

Typical X.25

Sub-Interface

Configuration Example

Therefore, the PVC 3 and PVC 4 mentioned above actually refer to the numbers of the logical channels between the router and the switch directly connected to it. However, on one side of this virtual circuit, the logical channel number can be used to identify this virtual circuit without causing misunderstanding. This is why no strict distinction is made between "virtual circuit" and "logical channel".

I. Networking Requirement

Multiple sub-interfaces are configured on a physical interface to connect with multiple peers of different network sections. In the following diagram, Router A is configured with two sub-interfaces, respectively interconnected with Router B and Router C.