[Click] Sample IP router configuration: ARPQuerier + SetIPAddress?

[Egi, Norbert]

You're right, I was missing that.
Thanks.

________________________________

From: Anand Kanagala [mailto:akanagala at google.com]
Sent: Wed 5/16/2007 16:55
To: Egi, Norbert
Cc: click at amsterdam.lcs.mit.edu
Subject: Re: [Click] Sample IP router configuration: ARPQuerier + SetIPAddress?



LookupIPRoute (from the thesis)  will replace the destination ip
annotation with the ip addres of the gateway.

See  http://www.read.cs.ucla.edu/click/elements/radixiplookup  for an
explanation.



On 5/16/07, Egi, Norbert <n.egi at lancaster.ac.uk> wrote:
> Hi,
>
> I'm creating a multiple forwarding path IP router configuration by extending Eddie Kohler's sample IP router configuration shown on page 64 in his PhD thesis. It looks to me that this configuration is a little bit incomplete. My concern is about packets destined to an IP address multiple hops away. In this case, the destination address annotation will be set to this address by the CheckIPHeader element and based on this annotations the ARPQuerier will send out a request for the MAC address of this IP, but as it is far away (not on the LAN the interface is attached to) no answer will arrive. Thus, the packet won't go anywhere.
>
> I think what is missing from that configuration compared to Linux's basic routing is the next-hop's IP address (i.e. the gateway to that destined network). As far as I understand the operation of the whole sample configuration, this could simply be solved by putting a SetIPAddress element with the proper next-hop's IP address as argument after the IPLookup element and probably the entries in the IPLookup will have to be sorted a bit different, as packets leaving on the same interface but going to different next-hops have to go through different SetIPAddress elements. As a consequence, by the time the packet arrives at the ARPQuerier it will always have the next-hop's IP address in its destination address annotation rather than the 'final' destination address, which can definitely be resolved by the ARPQuerier.
>
> My question is whether I'm right on this destination address annotation and ARPQuerier issue or I'm missing something?
>
> As far as I understand, the ARPQuerier sets the SRC MAC address to the one it has in its argument and sends out a request if it doesn't have the MAC for the IP address in the destination address annotation. When the response arrives it puts that MAC in the destination field of Ethernet header and emits it on its output.
>
> Thanks in advance,
> Norbert
>
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