Hi Simon,Am 04.04.2019 22:10:19, "Simon Kelley" <si...@thekelleys.org.uk> schrieb:
Sorry, I wasn't clear. A DHCP client can set a bit in the DHCP DISCOVER message that asks the DHCP server to broadcast the reply to it. The packet captures you posted showed exactly that. It's quite possible that the ThinkPad X260, _doesn't_ do this, so the reply is not broadcast.
thank you! Now I see, what you mean. And you are absolutley right. My X260 haven't set the broadcast flag, when looking into that packets.
A source of problems in the past has been firewall (iptables) rules that block packets sent to the 255.255.255.255 broadcast address. Such a rule on the machine running dnsmasq would break DHCP but only for clients which set the broadcast bit in the DHCPDISCOVER. I don't know if the packet capture happens before or after iptables, for the packet to be blocked, but still appear (as it did) in the packet capture, it would have to be before iptables.
I've run now several tests and found the cause. First, it's not iptables, they allow here broadcast, as it should be. It's my switch, who is not fowarding those broadcast pakets. It's an Netgear GS116Ev2. I am speechless, why this switch doesn't forward them. According to the WebUI, Broadcast Forwarding is enabled and not filtered. Conrad
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