Why cannot the serial interface be put into encapsulation?

[wfqk]

Hi, Do you think the following two cases are all normal? I think the first case is normal and the fastethernet does as normal, but the second one is serial port. The encapsulation command cannot be entered. Anyone have an idea for this? Thanks

First case:

R1(config-if)#int f0/1.101
R1(config-subif)#encapsulation dot1Q 10
R1(config-subif)#ip address 1.1.1.1 255.255.255.0

R1(config-subif)#do ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!

-------------------

Second case

R1(config-if)#int s0/0/0.109
R1(config-subif)#encapsulation ?
% Unrecognized command

[Richard Bradfield · Accepted solution]

HI,

You are talking about 2 different things here.Serial and Ethernet are physically different sort of interfaces with different characteristics .

On the Ethernet interface you are really defining Vlans for a trunk interface and the encapsulation command is the way it is done for each Vlan on that Ethernet trunk port.

Serial on the other hand the type of interface ( encapsulation) is done on the main interface (s0/0/0)

such as HDLC ( default) frame-relay,ppp sdlc-primary etc, and the secondary interface configuration are used to define parameters for the selected encapsulation such as the PVC for frame relay.

HTH

Richard

[wfqk]

Thank you for your reply. I think you are right. By default, serial port is hdlc, which means the interface cannot be configured as subinterface, right ? unless it is frame-relay. 

[Richard Bradfield]

that's about right