Thanks a lot Luca, it's crystal clear for me now that the controller HAS TO be involved in this arp reply task even if it's very basic...
Because there is no IP src in an ARP request 2013/3/4 Luca Prete <luca.pr...@garr.it> > Hi! > This could help: > http://technet.microsoft.com/en-us/library/cc758357%28v=ws.10%29.aspx at > paragraph "How ARP resolves media access controll addresses for remote > traffic". The thing is that OpenFlow switches (based on rules, actions...) > can't reply alone (without contacting the controller) to ARP request, > because they don't have ARP tables, protocols, etc....inside. > Thus, everytime they have to contact the controller sending back to the > host who made the ARP request a specific ARP reply. > > In your case: let's say you want to ping from H3 another host under S2 > (let's call it H2) with IP address 10.0.2.2. > - the host check with IP in its routing table and sees that to reach > 10.0.2.2 must goes through the gateway > - the host check in its ARP table for a corrispondence for the gateway but > it doesn't find anything > - a broadcast arp request is generated and it arrives to s1 that intercept > it for the first time asking what to do to the controller (with a packetin) > - The controller, analyzing headers, sees an ARP request from host 10.0.1.2 > - The controller build a unicast ARP reply directed to the host witch > requested, generating a packetout to the ingress port (on the switch) of > the requesting message. > Every time this reply changes depending on witch host generated the > request.....by the way, also if the address for any reason would remain the > same, switches can't manage alone ARP relies because they don't have the > ARP protocol (as normal routers have!). > - The controller (simulating the behaviour of the router) adds an ARP > entry (in a ad-hoc ARP table similar to MAC table of learning switch) a > tuple with the association 10.0.1.2 - MAC address. > > Hope to be clear, let me know if you need more help! > > Cheers, > > Luca > > Il 04/03/2013 08:45, Arnaud M ha scritto: > > Hi, thanks for response > > Just to specify : I want my switch (which is a "router" in this case) > responds to ARP request concerning only its ip Address (like it has to do) > > > > 2013/3/4 Luca Prete <luca.pr...@garr.it> > >> Hi! >> >> If you have a table con the controller with some records ip -- mac addr >> you can intercept broadcast arp request with the packet in message and >> answer with a unicast packet out to the machine witch generated the request >> (arp reply) >> >> Of course you COULD install a flowmod on the switch but it would be >> unusefull because arp request anyway would change every time, host by host. >> >> Anyway usually on the controller topology and device manager modules >> should help you ;) >> >> Luca P. >> >> Il giorno 04/mar/2013, alle ore 07:46, Arnaud M <arnau...@gmail.com> ha >> scritto: >> >> Hi everyone, >> >> I did the first part of this (great) tutorial and now i'm in the routing >> part and i'm wondering few things : >> >> 1 - why do we need 2 switch for this topology ? one should be enough >> right ? >> 2 - In the switching part, one didn't care about ARP reply/request... but >> here in routing mode we should, so here is my question : how do you craft >> ARP reply ? In the controller after a packet In message by sending a packet >> out message to the switch ? Or is there a way to push a flow that would >> match the ARP request and with actions would send an ARP reply ? >> 3 - What about ARP request ? When one need to replace ethernet >> destination... the controller should do it by using a packet out ? >> >> Thanks for your help >> >> Arnaud M >> >> _______________________________________________ >> openflow-discuss mailing list >> openflow-discuss@lists.stanford.edu >> https://mailman.stanford.edu/mailman/listinfo/openflow-discuss >> >> > >
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