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 <mailto: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 <mailto: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
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