frame relay sub-interface static mapping

[willowklan1]

Hi guys,

what if I don`t want to use the "frame relay interface dlci" command with inverse arp on my sub-interface on a frame relay topology?

I want to map the dlci to the IP address in a static manner on the sub-interface (multipoint) using the "frame relay map ip" command (no inverse arp ofcourse).

I configured the setup and all seems to be in order (i.e. "frame relay map" and "frame relay pvc" commands show everything correctly) but no ping can pass anywhere... why is that?

the ISP is configured correctly so the problem isn`t there.

the topology is fairly simple: a hub & spoke using the 10.0.0.0 network (photo at the bottom).

here are the relevant parts of the running-config + the map and pvc commands from router 1 (the hub)

=================================

router1

=======

interface Serial0/1/0

ip address 10.0.0.1 255.0.0.0

encapsulation frame-relay

no frame-relay inverse-arp

!

interface Serial0/1/0.1 multipoint

no ip address

frame-relay map ip 10.0.0.2 102 broadcast

frame-relay map ip 10.0.0.3 103 broadcast

no frame-relay inverse-arp

clock rate 2000000

=======

router 2

=======

interface Serial0/1/0

ip address 10.0.0.2 255.0.0.0

encapsulation frame-relay

no frame-relay inverse-arp

!

interface Serial0/1/0.1 multipoint

no ip address

frame-relay map ip 10.0.0.1 201

frame-relay map ip 10.0.0.3 203

no frame-relay inverse-arp

clock rate 2000000

======

router 3

======

interface Serial0/1/0

ip address 10.0.0.3 255.0.0.0

encapsulation frame-relay

no frame-relay inverse-arp

!

interface Serial0/1/0.1 multipoint

no ip address

frame-relay map ip 10.0.0.1 301

frame-relay map ip 10.0.0.2 302

no frame-relay inverse-arp

clock rate 2000000

==============

router1> show frame relay map

Serial0/1/0.1 (up): ip 10.0.0.2 dlci 102, static,

broadcast,

CISCO, status defined, active

Serial0/1/0.1 (up): ip 10.0.0.3 dlci 103, static,

broadcast,

CISCO, status defined, active

=====================

router1> show frame relay pvc

PVC Statistics for interface Serial0/1/0 (Frame Relay DTE)

DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/1/0.1

input pkts 14055 output pkts 32795 in bytes 1096228

out bytes 6216155 dropped pkts 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 32795 out bcast bytes 6216155

DLCI = 103, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/1/0.1

input pkts 14055 output pkts 32795 in bytes 1096228

out bytes 6216155 dropped pkts 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 32795 out bcast bytes 6216155

=============================================

thanks,

willow

[Peter Paluch · Accepted solution]

Hi Willow,

Your configuration has created a strange state in each of your routers:

• The Serial0/1/0.1 subinterface does not have an IP address configured. That means that all IP processing is disabled on this subinterface - it simply does not exist for IP, and you can also see that this interface does not show up in your show ip route output where all working IP-enabled interfaces should be visible. In short, the router will never try to use it to send IP packets, and if there was an IP packet received on it, it would be dropped. However, because you have used the frame-relay map commands on this subinterface, the DLCIs available to your router have been moved under this subinterface (that is unusable for IP).
• The Serial0/1/0 interface has an IP address configured but because all DLCIs available to your router have already been moved away to Serial0/1/0.1 subinterface, there are none that would be usable for Serial0/1/0. As a result, the Serial0/1/0 interface is unable to send and receive Frame Relay frames because all DLCIs have been claimed by the S0/1/0.1 subinterface.

Correctly, you should have both the IP address and the frame-relay map commands on the same interface, either on Serial0/1/0 or on Serial0/1/0.1. Please keep in mind that for a router, you cannot have two or more interfaces in the same IP network (which is what you are trying to achieve now). Even if you create a subinterface, that subinterface must be in a unique IP network.

Please feel welcome to ask further!

Best regards,
Peter

[willowklan1]

Hi Peter, 

thanks alot for the quick (and detailed) respone. seems I forgot to put IP addresses on the sub-interfaces... how embarrassing! 

so just to get this one clear: I do not have to use the "frame relay interface dlci" command with inverse arp on the sub-interfaces. I might as well use the "frame relay map ip" statement with "no inverse arp" in the background.

if that is so, why do I read that there can be no self-ping on an multipoint sub-interface? after configuring the missing IP addresses, all you need to do is add 

"frame relay map ip 10.0.0.1 102" 

on the hub, and voia-la, you can ping yourself. you can do that on the spokes as well, just choose a dlci and map it to yourself and you`ll get a self-ping. so why everyone says it is impossible? 

thanx again,

willow

[Peter Paluch]

Hi Willow,

so just to get this one clear: I do not have to use the "frame relay interface dlci" command with inverse arp on the sub-interfaces. I might as well use the "frame relay map ip" statement with "no inverse arp" in the background.

Yes, it would seem so. In fact, by referencing a DLCI in a frame-relay map command, the InverseARP on that DLCI is deactivated automatically; more precisely, the router stops sending out Queries but it will still respond to a received Query in case the other side is asking.

I have, however, always found it to be more understandable to use both frame-relay interface-dlci and frame-relay map commands on subinterfaces. By using frame-relay interface-dlci, you are making it very clear that you want that particular DLCI to be anchored to the specific interface. Every DLCI that has not been explicitly tied to a subinterface, either using the frame-relay interface-dlci or the frame-relay map command, will be tied to the physical interface.

why do I read that there can be no self-ping on an multipoint sub-interface?

As you have correctly explained yourself in subsequent post, this is not correct. It is true that you cannot ping yourself without additional configuration. However, as soon as you map your own IP address to a DLCI that goes to another router, and that router knows the mapping back to you, the ping will start working. The trick, however, is that the single ping packet truly makes a full round across the DLCI to the remote end and back before it is received by the originating router. The reply to this ping will again be sent to the other end and back before it is "received".

Best regards,
Peter

[willowklan1]

Hi Peter,

thanks alot mate. that really cleared some issues.

[Peter Paluch]

Hi Willow,

You're very much welcome!

Best regards,
Peter