Create 2 from 1 Physical Link

Like Magic! WoW, no magic in networking :d. As like in title create 2 logical link from 1 physical link, actually not just 2 link can we create, can more than 2 link. Physical link in here are Serial and Ethernet, but now I just use Serial link with frame-relay encapsulation, may be next time for Ethernet. Logical link is use subinterface Serial interface. Serial interface link identic with WAN and use E1/T1 dedicated link.

What is purpose separate 2 or more link from 1 physical link :

o traditional separate traffic type
o separate VPN with internet traffic
o out-of-band, separate main traffic like Internet or Data with signal or management traffic
o etc.

Example configuration with 1 physical link attach 2 Cisco router (R1 and R2).

R1#
frame-relay switching

interface Serial1/0
 no ip address
 encapsulation frame-relay
 serial restart_delay 0
 no frame-relay inverse-arp
 frame-relay intf-type dce

interface Serial1/0.1 point-to-point
 ip address 10.10.1.1 255.255.255.0
 frame-relay interface-dlci 100   

interface Serial1/0.2 point-to-point
 ip address 10.10.2.1 255.255.255.0
 frame-relay interface-dlci 200   

R2#
interface Serial1/0
 no ip address
 encapsulation frame-relay
 serial restart_delay 0
 no frame-relay inverse-arp

interface Serial1/0.1 point-to-point
 ip address 10.10.1.2 255.255.255.0
 frame-relay interface-dlci 100   

interface Serial1/0.2 point-to-point
 ip address 10.10.2.2 255.255.255.0
 frame-relay interface-dlci 200   

R1#sh frame-relay ?
  end-to-end     Frame-relay end-to-end VC information
  fragment       show frame relay fragmentation information
  ip             show frame relay IP statistics
  lapf           show frame relay lapf status/statistics
  lmi            show frame relay lmi statistics
  map            Frame-Relay map table
  multilink      Show Multilink Frame Relay bundle information
  pvc            show frame relay pvc statistics
  qos-autosense  show frame relay qos-autosense information
  route          show frame relay route
  svc            show frame relay SVC stuff
  traffic        Frame-Relay protocol statistics
  vc-bundle      FR VC-Bundle
  vofr           Show frame-relay VoFR statistics

R1#sh frame-relay map
Serial1/0.2 (up): point-to-point dlci, dlci 200(0xC8,0x3080), broadcast
          status defined, active
Serial1/0.1 (up): point-to-point dlci, dlci 100(0x64,0x1840), broadcast
          status defined, active

R1#sh frame-relay pvc 100

PVC Statistics for interface Serial1/0 (Frame Relay DCE)

DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0.1

  input pkts 16            output pkts 16           in bytes 3044      
  out bytes 3044           dropped pkts 0           in pkts dropped 0         
  out pkts dropped 0                out bytes dropped 0         
  in FECN pkts 0           in BECN pkts 0           out FECN pkts 0         
  out BECN pkts 0          in DE pkts 0             out DE pkts 0         
  out bcast pkts 6         out bcast bytes 2004      
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
  pvc create time 00:25:40, last time pvc status changed 00:05:24