FR: invarp - learning from requests ?

Answered Question
Aug 5th, 2009

hello

According to RFC2390: " Upon receiving an InARP request, a station may put the requester's protocol address/hardware address mapping into its ARP cache as it would any ARP request."

If i have R1,R2,R3 with R1 as the hub, and i will configure:

- on R2 static mapping to R3

- on R3 static mapping to R2

- on R1 inverse arp

R1 after receiving LMI will send inverse arp request to R2 and R3 which will respond to this packet. The question is: will R2 and R3 add dynamic mapping for that DLCI/IP received in this inverse-arp request ?

Thanx

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Correct Answer by Peter Paluch about 7 years 4 months ago

Hello,

On Cisco routers, they will. The Cisco routers learn also by receiving requests, not just by receiving replies.

However, this is an implementation dependent behavior, I believe. The RFC clearly does not require that FR DTE devices learn InverseARP mappings also by requests. I can imagine a more naive (or perhaps, more strict) implementation that learns only using replies.

Best regards,

Peter

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Correct Answer
Peter Paluch Wed, 08/05/2009 - 02:25

Hello,

On Cisco routers, they will. The Cisco routers learn also by receiving requests, not just by receiving replies.

However, this is an implementation dependent behavior, I believe. The RFC clearly does not require that FR DTE devices learn InverseARP mappings also by requests. I can imagine a more naive (or perhaps, more strict) implementation that learns only using replies.

Best regards,

Peter

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