Cisco single-Arm routing configuration, illustrated examples

Cisco single-ARM routing configuration

One-arm routing, which is to set up multiple logical subinterfaces on the router, one VLAN for each sub-interface. The data on each sub-interface is passed on the physical link to be labeled encapsulated. Cisco devices support ISL and 802.1q (dot1q) protocols. 

The difference between dot1q and ISL: dot1q is a generic VLAN protocol model for various products, and dot1q is a universally used standard for all switches and routing devices. Supports more than 1024vlan, while ISL supports up to 1024 VLANs. ISL is a proprietary protocol for Cisco devices and is suitable for Cisco devices. The ISL (Interior switching Link) Inter-switch protocol is used to implement VLAN trunking between Cisco switches. It is a packet-tagging protocol that is composed of a standard Ethernet frame and associated VLAN information for frames sent on an ISL-capable interface.

PC1:IP:172.16.3.1/24 gw:255.255.255.0

PC2:IP:172.16.4.1/24 gw:255.255.255.0

S1:

Switch>enable

Switch#vlan Database

Switch (VLAN) #vlan 30

Switch (VLAN) #vlan 40

switch# Configure terminal

Switch (config) #int fastethernet 0/1

Switch (config-if) #switchport Access VLAN 30

Switch (config-if) #int F0/2

Switch (config-if) #switchport Access VLAN 40

Switch (config-if) #int F 0/24

Switch (config-if) #switchport mode trunk (set the interface to trunk mode)

Switch (config-if) #switchport trunk allowed VLAN All (runs all VLANs through)

If you want to draw multiple ports of the switch to a VLAN, use the following command:

Switch-1 (config) #interface range fastethernet 0/1-10
Switch-1 (config-range) #switchport Access VLAN 30

RT1:

Router>enable

Router#configure Terminal

Router (config) #int fastethernet 0/0.1 (enter sub-interface)

Router (config-subif) #encapsulation dot1q 30 (Encapsulating dot1q Protocol, establishing an association with VLAN30)

Router (config-subif) #ip add 172.16.3.254 255.255.255.0

Router (config-subif) #int F 0/0.2

Router (config-subif) #encapsulation dot1q 40 (Encapsulating dot1q Protocol, establishing an association with VLAN40)

Router (config-subif) #ip add 172.16.4.254 255.255.255.0

Router (config-subif) #int F 0/0

Router (config-if) #no shutdown (Start f0/0 interface, including all sub-interfaces)

Complete. Vlan30 can communicate with VLAN40.