[Dnsmasq-discuss] ARP ignores DHCP ACKs !
albert.aribaud at free.fr
Wed Dec 25 13:52:58 GMT 2013
Le 25/12/2013 12:07, Nikita N. a écrit :
>> The important point for your situation is that it's perfectly normal to
>> see a DHCP client make an ARP request as part of the address-aquisition
>> process, and for that ARP request to go un-answered.
> Hi Simon :)
> Yes, that I understood very clearly, such unanswered ARPs are normal,
> everybody told me that.. :))
> As matter of fact, such ARPs appear in XP and Vista too, but 2/3 frames
> at most..
> On Win7 they appear in number of 50/100 frames, multiple times, that
> raised my suspects..
> Still, would like to ask you about ICMP frames, if I can.. ;)
> because you say client uses ARP, the GW uses ICMP.. right?
Not the gateway, the DHCP server (which may or may not be a gateway).
> Well, I cant see that.. the only ICMP I see are from the client to GW,
> sent after DNS answers from dnsmasq (dnsmasq runs on GW)..
You mean the client pings the IP of the gateway? Well, obviously I don't
have the same setup as you have, but I have two Windows machines in my
LAN, and none of them ever emits ICMP echo requests unless someone
actually runs a ping on them in a DOS window. They do emit ARP requests,
though, just like any other hosts in my LAN.
> As I wrote, I set to drop all in/out ICMP frames on GW (iptables), and
> still connection keeps alive allright on Vista, XP and Linux..
> But on Win7 cant see the light.. lots of those unanswered ARPs, few ARP
> req about who has GW, few Netbios, ipv6 frames and other useless
> protocol frames, stop.. Win7 gives up, red X on connection, finish.. any
> hint comes in your mind about that?
Yes: do a Wireshark / tcpdump on both the DHCP server and client, force
a DHCP exchange, see what is emitted by one machine and not received by
> About ICMP in general, since Im serving only local pages to client, is
> it ok in my local network to set drop all ICMP on GW?
> Thanks :)
This is unrelated to dnsmasq, but here is a quick answer:
ICMPv6: you can't block it if you want routing to happen at all.
ICMPv4: you might experience issues between your local machines and the
What's the point of blocking ICMP on the local network? I can understand
blocking IMCP ECHO REQUESTs coming from the Internet and directed at
your local network (well, at those machines from your LAN which can be
addressed from the Internet); but local traffic is not really an issue.
Or is it?
More information about the Dnsmasq-discuss