Sub-Interface question

[bmellis1984]

So here's my question; do sub-interfaces automatically route traffic without a routing protocol enabled?  This is just one little detail either I missed or forgotten.

interface Serial0/0
no ip address
encapsulation frame-relay
clock rate 2000000
!
interface Serial0/0.1 point-to-point
ip address 192.168.0.1 255.255.255.248
frame-relay interface-dlci 103
!
interface Serial0/0.2 point-to-point
ip address 192.168.0.9 255.255.255.248
frame-relay interface-dlci 102
!
interface Serial0/0.3 point-to-point
ip address 192.168.0.17 255.255.255.248
frame-relay interface-dlci 101
!

!


!

R1#show ip route

Gateway of last resort is not set

192.168.0.0/29 is subnetted, 3 subnets
C 192.168.0.8 is directly connected, Serial0/0.2
C 192.168.0.0 is directly connected, Serial0/0.1
C 192.168.0.16 is directly connected, Serial0/0.3

[Richard Burts · Accepted solution]

The answer to your question about subinterfaces is the same as the answer to a similar question about physical interfaces. On an IOS router any interface (either physical or subinterface) in the state of up/up which has an appropriate IP address and subnet mask configured will route for that address locally. So in your example any device connected on one of your subinterfaces will be able to communicate with devices on any of the other subinterfaces (their traffic will be routed). To get to anything remote you would need a static route or would need a dynamic routing protocol.

HTH

Rick

[bmellis1984]

Thanks I think I understand now. I appreciate the quick response.

[Richard Burts]

You are welcome. I am glad that my explanation was helpful. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions that have helpful information.

I hope to see you continue to be active in the forums.

HTH

Rick