netdev - Re: [PATCH] ipv4/ipv6: check hop limit field on input

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Message-ID: <4A24F247.2040406@dev.6wind.com>
Date:	Tue, 02 Jun 2009 11:35:03 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	John Dykstra <john.dykstra1@...il.com>
Cc:	Brian Haley <brian.haley@...com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Florian Westphal <fw@...len.de>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv4/ipv6: check hop limit field on input

John Dykstra wrote:
> On Mon, 2009-06-01 at 14:55 -0400, Brian Haley wrote: 
>> 'ping6 -t 0 host' does work however.  The problem I see is that if you ping a system,
>> if it's a host it will respond, if it's a router it won't - the RFCs don't
>> explicitly state the host should drop the packet.  
> 
> There are two cases--an echo request to an address assigned to a
> router's interface, and to an address _beyond_ the router on another
> link.
> 
> Any given interface on a router can have forwarding dynamically enabled
> or disabled.  I don't remember prescribed echo request or hop limit
> behavior changing depending on the forwarding enable, so it seems that
> if you ping an address assigned to a router's interface, the router is
> expected to follow the (apparently unwritten) host rules.  
Good point.

> 
> Echo requests forwarded by a router should obviously have the hop limit
> decremented and checked.
> 
>> I don't know if that difference
>> in behavior is desired.  Do we know how any other OSes behave?
> 
> FWIW, the random BSD flavors I have on hand all check hop limit when
> forwarding, but not when processing local ingress traffic.
> 
> Also FWIW, as I remember, the TAHI tests only check hop limit behavior
> on forwarded traffic.
Right.

> 
> Nicolas, what's driving your patch?  Are you trying to align slow path
> behavior with one of the 6WIND fast path implementations?
No. I'm just checking RFC conformance ;-)


Nicolas

> 
>   --  John
> 
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