Configuring 2 or more subnets on the same Frame Relay T1

[asidney]

my question is on how to configure 2 or more subnets on a single Frame Relay T1 interface using the same DLCI (dlci 851 in this case)?

In other words, I need to configure two subnets: 10.5.15.1/240 and 10.5.15.17/240 on a T1 that terminates at my Cat 6509. I have a single dlci (dlci 851) that I need to map or associate these subnets to locally.

[Edison Ortiz]

You create subinterfaces.

interface s0/0

encapsulation frame-relay

frame-relay lmi-type [ansi | cisco]

interface s0/0.1

ip address 10.5.15.1 255.255.255.240

frame-relay interface-dlci [remote dlci]

interface s0/0.17

ip address 10.5.15.17 255.255.255.240

frame-relay interface-dlci [remote dlci]

Please rate helpful posts.

Thanks

[Richard Burts]

Edison

In the original post Anthony was very clear that he had a single DLCI. Your suggested solution of configuring subinterfaces requires 2 DLCIs.

I am not clear why Anthony needs two subnets on a single DLCI which is inherently a point to point connection. But if he does need two subnets then I believe that the appropriate solution is to configure secondary address on the frame relay interface. It could be done on the primary physical interface or could be done on a subinterface. Without knowing more about the environment and the requirements I would probably suggest configuring a single subinterface with secondary addressing. The configuration would look something like this:

interface s0/0.851

ip address 10.5.15.1 255.255.255.240

ip address 10.5.15.17 255.255.255.240 secondary

frame-relay interface-dlci 851

HTH

Rick

[Edison Ortiz]

Rick, you are right. My apologies for posting an incorrect suggestion.

[Richard Burts]

Edison

Your instincts were right. Your solution is a common and very good solution - just for a slightly different question.

HTH

Rick

[ilya.varlashkin]

I'd add one more thing - the sub-interface has to be point-to-point, so any traffic matching subnet but not matching local interface address will be send out. If the sub-interface is point-to-multipoint, or if this configured on main interface then static mapping for remote secondary address will be necessary since InARP apparently works only on primary address.

[asidney]

Thanks for the reponse. However, configuring subinterfaces was not the issue. I've done that many times before. What was unique this time is that I needed to apply the same dlci to both subintfs. IOS complains when you try to do this because it knows the dlci is already configured on the first subintf. What I realized I had to do was apply the dlci to the primary interface only. This seemed to have worked.

interface Serial1/1/3:0

no ip address

encapsulation frame-relay

shutdown

no fair-queue

frame-relay interface-dlci 851

frame-relay lmi-type ansi!

interface Serial1/1/3:0.2 point-to-point

bandwidth 1544

ip address 10.5.15.1 255.255.255.240!

interface Serial1/1/3:0.3 point-to-point

bandwidth 1544

ip address 10.5.15.17 255.255.255.240

[zhiqiang.yan]

I think you don't need to use subinterface.

like this:

interface s0/0

ip address 10.5.15.1 255.255.255.240

ip address 10.5.15.17 255.255.255.240 secondary

frame-relay interface-dlci 851

[asidney]

This makes sense and is much easier.

Thanks for the info! I'll try it.