How Frame-Rely Inverse ARP work ?

[ganpatspatil]

How Frame-Rely Inverse ARP work ?And what is the use of "frame-relay map ip 10.10.1.11 101 broadcast" brodcast word in this command ?

[Danilo Dy]

Frame-Relay Inverse ARP works by mapping a known Layer 2 address (e.g. DLCI) to an unknown Layer 3 address (e.g. IP Address).

"frame-relay map ip 10.10.1.11 101 broadcast"

- maps IP Address 10.10.1.11 to DLCI 100

- broadcast keyword is added to dynamic maps learned via Inverse ARP

[ganpatspatil]

Thnaks for reply....

Is there any role of Frame-rely switch while replying to INVERSE-ARP request ?

Who will reply to inverse ARP pakect ?

[Danilo Dy]

The remote device interface. InArp uses a query on each virtual circuit to determine the IP Address of the interface at the remote end.

Difference and similarity between Ethernet and Frame-Relay

- Ethernet ARP Request knows the Layer 3 Address, and requests the Layer 2 Address (MAC).

- Frame Relay Inverse ARP knows the Layer 2 Address (DLCI) and request the Layer 3 Address (Next-Hop IP Address).

Frame-Relay Inverse ARP is not required in point-to-point interface. You can disable it by executing "no frame-relay inverse arp" at the itnerface. However, Inverse ARP Reply cannot be disabled. So even you disabled Inverse ARP in a Frame-Relay Interface, it will still respond to Inverse ARP query.

[ganpatspatil]

Hi Medan,

DO you have any document on the fram-rely ?

Regards

Ganpat Patil

[Danilo Dy]

I use this link when I work with Frame Relay many years ago :) http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml

[ganpatspatil]

Is compulsoary to assign The DLCI number to each interface ?

[Danilo Dy]

No.

DLCI mapping can be accomplished by either static or dynamic.

Static mapping is to map the remote IP to a DLCI. .e.g

frame-relay map ip 10.10.1.11 101 broadcast

Dynamic mapping is to let Inverse ARP do its job.

[ganpatspatil]

do you mean if i configured,

ROUTER A:-

interface serial 0

encapsulation frame-relay

ip address x.x.x.x

ROUTER B:-

interface serial 0

encapsulation frame-relay

ip address y.y.y.y

In above configuration Inverse ARP is disabled.Will it work ?

so in which Case i have to assgin DLCI Number to the interface?

[John Blakley]

My understanding is that inverse arp is enabled by default.

In each of your interfaces, you would do:

int s0

encaps frame-relay

no frame-relay inverse-arp

frame-relay map ip 192.168.1.2 201 broadcast

To see if inverse arp is enabled, you can do a "sh frame-relay map", and if you have mapped ip addresses, then it's enabled. If you get back nothing, it's already disabled, and you'll need to manually map your ip addresses.

HTH,

John

[Lassek]

for the benefit of new readers

The command "encapsulation frame-relay" will enable by default Inverse ARP on all interfaces and subinterfaces, so with that configuration inverse ARP will be enabled and the config will work as In ARP will take care of doing the maping DLCI to IP dynamically. check "show frame-relay map".

It's also worth noting that the command encapsulation frame-relay will also by default associate all DLCIs to the physical interface, so there is no need to use the command "frame-relay interface-DLCI" on the physical interface. However, this command is compulsory on point-to-point subinterfaces though, it tells the IOS "this specific DLCI is associated with this subinterface".

Regards,

Raul