The Routing Over Large Clouds Mailing List Archive by date

[Bruce Cole <bcole@cisco.com>]

> If the normal routed path over the NBMA travels thru routers A, B, C and D,
> where routers B and C are transit routers,  wouldn't this lead to
> the generation of three seperate "short cut" link layer connections (in the
> case of a connection-oriented NBMA like ATM) for the same packet?
> For example, 
>     - router A receives a packet and determines that it is to be forwarded
>         to its NBMA interface.  it sends a NHRP request and forwards
>         the packet to router B,
>     - router B receives a packet and determines that it is to be forwarded
>         to its NBMA interface.  it sends a NHRP request and forwards
>         the packet to router C, etc
>     - once the NHRP replies return to routers A, B and C, they each establish
>         their own "short cut" connections to D.
> 
> If this is indeed the case, then option (c) above should be removed in favor
> of one of the remaining two.  Am I missing out on something?

You are missing: rate limiting.  Routers B & C need not transmit multiple
NHRP request packets.  They can drop NHRP packets which exceed whatever your
desired rate is.

The benefit of option (c) is that your IP traffic is not delayed until
address resolution (or worse - VC establishment) has completed.