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Message-ID: <1468217682.5588.4.camel@synopsys.com> Date: Mon, 11 Jul 2016 06:15:58 +0000 From: Alexey Brodkin <Alexey.Brodkin@...opsys.com> To: "russell@...sonaltelco.net" <russell@...sonaltelco.net> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "lede-dev@...ts.infradead.org" <lede-dev@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "davem@...emloft.net" <davem@...emloft.net>, "aczlan+ledev@...il.com" <aczlan+ledev@...il.com>, "linux-snps-arc@...ts.infradead.org" <linux-snps-arc@...ts.infradead.org> Subject: Re: [LEDE-DEV] DHCP via bridge in case of IPv4 Hi Russel, On Sun, 2016-07-10 at 00:19 -0700, Russell Senior wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > "Alexey" == Alexey Brodkin <Alexey.Brodkin@...opsys.com> writes: > Alexey> Hi Aaron, > Alexey> On Sat, 2016-07-09 at 07:47 -0400, Aaron Z wrote: > > > > > > > > On Sat, Jul 9, 2016 at 4:37 AM, Alexey Brodkin > > > <Alexey.Brodkin@...opsys.com> wrote: > > > > > > > > > > > > Hello, > > > > > > > > I was playing with quite simple bridged setup on different boards > > > with > very recent kernels (4.6.3 as of this writing) and found one > > > interesting > behavior that I cannot yet understand and googling > > > din't help here as well. > > > > > > > > > > > > My setup is pretty simple: > > > > ------------- ------------------ ------------------------- > > > > > > > > > > > > > > > > > > > HOST | | "Dumb AP" | | Wireless > > > client | > > with DHCP |<----->(eth0) (wlan0)<----->| > > > attempting to | > > server | | \ br0 > > > / | | get settings via DHCP | > > > > ------------- ------------------ ------------------------- > > > > > > > > > > > > * HOST is my laptop with DHCP server that works for sure. > * > > > "Dumb AP" is a separate board (I tried ARM-based Wandboard and > > > ARC-based > AXS10x boards but results are exactly the same) with > > > wired (eth0) and wireless > (wlan0) network controllers bridged > > > together (br0). That "br0" bridge flawlessly > gets its settings > > > from DHCP server on host. > * Wireless client could be either a > > > smatrphone or another laptop etc but > what's important it should > > > be configured to get network settings by DHCP as well. > > > > > > > > > > > > So what happens "br0" always gets network settings from DHCP server > > > on HOST. > That's fine. But wireless client only reliably gets > > > settings from DHCP server > if IPv6 is enabled on "Dumb AP" board. If > > > IPv6 is disabled I may see that > wireless client sends "DHCP > > > Discover" then server replies with "DHCP Offer" but > that offer > > > never reaches wireless client. > > > > > > > > > Do you have WDS enabled? If not, DHCP has issues in that scenario: > > > https://wiki.openwrt.org/doc/howto/clientmode > If the Dumb AP's wireless interface is in ap-mode, then this shouldn't > be an issue. It's only client-mode interfaces that have trouble with bridging. > > I'd suggest running tcpdump on the Dumb AP's wireless interface and the > client's wireless interface and see which of them sees the various parts > of the DHCP handshake. So I did but for DHCP server and wireless client (had no tcpdump on Dump AP at the moment). That's what I see on the server: ----------------------------->8------------------------------- No. Time Source Destination Protocol Length Info 3 0.151181000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 11 2.760796000 10.42.0.1 10.42.0.13 DHCP 342 DHCP Offer - Transaction ID 0x31dc321f 14 5.220985000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 15 5.221150000 10.42.0.1 10.42.0.13 DHCP 342 DHCP Offer - Transaction ID 0x31dc321f 23 15.649835000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 24 15.650017000 10.42.0.1 10.42.0.13 DHCP 342 DHCP Offer - Transaction ID 0x31dc321f 32 25.648589000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 33 25.648758000 10.42.0.1 10.42.0.13 DHCP 342 DHCP Offer - Transaction ID 0x31dc321f 43 35.864567000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 48 38.832837000 10.42.0.1 10.42.0.13 DHCP 342 DHCP Offer - Transaction ID 0x31dc321f ----------------------------->8------------------------------- That's on the wireless client: ----------------------------->8------------------------------- No. Time Source Destination Protocol Length Info 1171 94.192971000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 1182 99.263686000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 1185 109.692642000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 1186 119.691474000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f 1190 129.907507000 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x31dc321f ----------------------------->8------------------------------- I'll try to capture data from Dumb AP sometime soon and will reply to the thread. -Alexey
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