subinterface question

tha_dub

I'm just going over some frame relay chapters and in one section it explicitly states not to have an ip address under the physical interface when using sub interfaces with frame relay.

This reminded me of a question in the boson test where they have a ROAS with the native vlan IP on the physical interface and the vlan 5 on a subinterface as the correct answer.

I guess my question is why can't you do it with frame relay but ROAS is okay?

(I did have a guess) Does it have to do with split horizon?

Thanks!

Slowhand

I think there must've been something funky with that Boson test. When you create subinterfaces, the physical interface should not have an IP address. Chances are, there was meant to be two subinterfaces, one with the main VLAN IP and the other with the VLAN 5 IP.

Here are some how-to's from various sites to illustrate:
Initial Configurations for OSPF over Frame Relay Subinterfaces
Configuring InterVLAN Routing and ISL/802.1Q Trunking
Frame Relay Subinterfaces And Split Horizon
Configuring And Troubleshooting Router-On-A-Stick

PhildoBaggins

yeppers, the interface should have the "no ip address" command present. Only the sub interfaces should be addressed.

networker050184

You can use the main interface with an IP on for the native on dot1q. You don't have to use the native command under a sub interface. I believe you can use frame-relay on sub interfaces and the main interface at the same time also. I'm not 100% sure though.