Re: [Autoconf] what's a router

Alexandru Petrescu <alexandru.petrescu@gmail.com> Thu, 05 August 2010 11:25 UTC

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Date: Thu, 05 Aug 2010 13:25:42 +0200
From: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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To: Ulrich Herberg <ulrich@herberg.name>
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Subject: Re: [Autoconf] what's a router
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Le 05/08/2010 12:29, Ulrich Herberg a écrit :
> Alex,
>
>> [...] To me a router is a device and its software doing this: - has
>> a routing table called such. - does longest-prefix match algorithm
>> to search in it.  This operation is not specified (no RFC) but it
>> is there everywhere in every router, thanks BSD. - includes that
>> route.h I believe as CP said. - has multiple interfaces.
>>
>> In a sense every other host (my Windows PC) is a router because it
>>  does all these things.  My PDA, my cell phone, are all routers.
>
> Well, that seems like a strange definition of a router. In a recent
> mail of Teco, he summarized the three typical definitions of
> routers. And as Henning said, MANET routers may have a single
> interface and still perform routing (in the sense of receiving an
> incoming IP packet not destined to the receiving router itself,
> looking up the next hop from the routing table using longest-prefix
> match, and retransmission on the appropriate network interface).

If the 'appropriate' network interface is always the same interface
becuase there's only one, then... why the need to look it up in a
routing table?  Why the need to select among other routes?

Or is it simply because the longest-prefix match algorithm is there
everywhere, works with any socket () program setting the dst IP address
field, and with a default route set there.

Just because the longest-prefix match algo is called everytime a packet
is sent does not mean to me it _should_ be called.

An optimizer human looking at a router with a single interface and a
single-entry routing table would surely get rid of this latter
including its algo.  Because this happens at each packet and takes
unnecessary time.  And removing this table and algo makes it a no-router.

Alex

>
> Ulrich
>