Frame Relay configuration - please help

[Marcos.Zimmermann]

Hi,

I had configured the following on each of my serial interfaces of both routers connected together by a dce/dte cable:

router A:

interface Serial0

ip address 192.168.100.1 255.255.255.0

encapsulation frame-relay

frame-relay interface-dlci 140

router B:

interface Serial0

ip address 192.168.100.2 255.255.255.0

encapsulation frame-relay

frame-relay interface-dlci 150

The serial interface is up but the line protocol is down. I have no idea what I did wrong...

Regards

Marcos

[Georg Pauwen]

Hello,

try the following (I am assuming that router A is your DCE end):

router A:

-->frame-relay switching

interface Serial0

ip address 192.168.100.1 255.255.255.0

encapsulation frame-relay

--> frame-relay map ip 192.168.100.2 102 broadcast

--> frame-relay intf-type dce

--> clock rate 64000

router B:

interface Serial0

ip address 192.168.100.2 255.255.255.0

encapsulation frame-relay

frame-relay map ip 192.168.100.1 102 broadcast

If router B is your DCE end, change the config accordingly. You can find out which end is the DCE and which the DTE by doing a ´show controller serial 0´on each router.

Regards,

Georg

[Marcos.Zimmermann]

Hi Georg,

thank your for your fast answer. This configuration works ;-) I think the "frame-relay intf-type dce" was the key point I didn't configured. I remember, every time I use "sh int ser 0" the interface of each router displays "frame relay DTE". Now router A display DCE ...

Regards

Marcos

[Georg Pauwen]

Hallo Marcos,

no problem, viel Glück.

Georg

[Marcos.Zimmermann]

Hi,

now I have some other problems when I use the configuration above... The router A has some other routes, that are not advertised via OSPF. When I use HDLC as encasulation everything is fine and the routes are advertised. As soon as I configure the interfaces for frame-relay the routes are not advertised... The other problem is, that I can't ping the local router interface from the router console, but the other end of the point to point link. This problem exists only when I configured the interfaces for frame.relay, if I use HDLC everything is fine...

Do you have some idea`s?

Regards

Marcos

[Georg Pauwen · Accepted solution]

Hello Marcos,

OSPF sees the Frame Relay interface as a non-broadcast network interface, and that´s why neighbor relationships are not established. Either manually configure a neighbor on one side in router configuration mode with the ´neighbor X.X.X.X´ command, where X.X.X.X is the IP address of the other side, or change the network type to broadcast with the interface configuration command ´ip ospf network broadcast´, make sure to configure that on both interfaces.

Regarding the second problem: map the local ip address to a DLCI in order to ping your own interface. Let´s say your local interface address is 192.168.1.1, add the following statement to your configuration:

frame-relay map ip 192.168.1.1 102

Here is the ´éxtended´ exlanantion for that problem, if you don´t mind a little reading:

Why am I unable to ping my own interface address?

A. You cannot ping your own IP address on a multipoint Frame Relay interface. To make a ping successful on a serial interface, an Internet Control Message Protocol (ICMP) echo request packet must be sent, and an ICMP echo reply packet must be received. Pings to your own interface address are successful on point-to-point subinterfaces or high-level data link control (HDLC) links because the router on the other side of the link returns the ICMP echo and echo reply packets.

The same principle also applies with multipoint (sub) interfaces. To successfully ping your own interface address, another router must send back the ICMP echo request and the echo reply packets. Because multipoint interfaces can have multiple destinations, the router must have Layer 2 (L2) to Layer 3 (L3) mapping for every destination. Because mapping is not configured for our own interface address, the router does not have any L2 to L3 mapping for its own address and does not know how to encapsulate the packet. That is, the router does not know which data-link connection identifier (DLCI) to use to send echo request packets to its own IP address resulting in encapsulation failure. To be able to ping its own interface address, a static mapping must be configured pointing towards another router over the Frame Relay link which can send back the ICMP echo request and reply packets.

HTH,

Georg

[Marcos.Zimmermann]

Hi Georg,

thank you for your help. Now it works fine.

Regards

Marcos