Re: e1000 and 802.1ad/stacked vlan tagging
On Mon, 28 Aug 2006 13:53:36 -0700 Brandeburg, Jesse [EMAIL PROTECTED] wrote: I tried enlarging both real-device and first vlan interface mtu but that does not work out. I really thought that the visible device setting of mtu=1500 should have worked out and that the driver (or some code in between) should have corrected the allowed frame size to reflect the actual setup, not? unfortunately I believe that your hardware MTU on the base interface MUST be adjusted in order to do stacked vlans because the vlan code doesn't fragment packets, it just inserts tags. The e1000 hardware is capable of inserting/stripping 1 level of tags without dropping overlong frames, but cannot seamlessly handle 1+n levels of inserted tags. Transmit, we don't care how long the frames are that are given to us (the driver doesn't enforce MTU on transmit) but on receive we have limited space so it is important that each frame fit into the allocated buffer (including CRC). Please try MTU 1508 on eth0 (base interface only), as that configuration worked for me. Hello Jesse, I can confirm that the setup seems to work if enlarging the hw if mtu to 1508. This is good. Nevertheless I think that the receive buffer size of a physical device should always be MAX(all virtual device mtu + tags and the like), you know what I mean. If I enlarge the basic mtu this may or may not have drawbacks concerning the traffic routed directly via this interface. Obviously the setup is somehow not consistent, as everything works well without tuning mtus as long as you use only 1 tag. I always thought that the driver uses at least hard_header_len + mtu as buffer size which should be correct even in stacked setup. Only this information doesn't make it to the driver level, right? -- Regards, Stephan von Krawczynski - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: e1000 and 802.1ad/stacked vlan tagging
Hello Jesse, thank you for answering anyway. Though I think your answer covers only the obvious half of the problem. Indeed one might think that this solves the issue - as long as there are only linux kernels involved. Unfortunately my setup is a bit more complicated in terms of hardware. So I should have probably clarified the question this way: how do you configure the interface in a manner that packets with data length of 1500 get transferred, and not only 1496 ? I tried enlarging both real-device and first vlan interface mtu but that does not work out. I really thought that the visible device setting of mtu=1500 should have worked out and that the driver (or some code in between) should have corrected the allowed frame size to reflect the actual setup, not? Regards, Stephan PS: crossposted to both lists, list-members keep in mind I am not subscribed when answering! Thank you. On Mon, 28 Aug 2006 10:23:09 -0700 Brandeburg, Jesse [EMAIL PROTECTED] wrote: Stephan von Krawczynski wrote: Hello Jesse, sorry to bother you directly, but since you did the patch for my e1000 interrupt problem last time (February) I hope you have a short-hand idea for my current issue, too. I am trying to make stacked vlan tagging work under kernel 2.4 with e1000. Generally I do this on two boxes connected back-to-back: ifconfig eth0 up vconfig add eth0 4094 ifconfig eth0.4094 up vconfig add eth0.4094 1 ifconfig eth0.4094.1 192.168.1.1 netmask 255.255.255.0 broadcast 192.168.1.255 up (of course the second box gets another ip, lets assume .2). if you do a ping -s 1472 192.168.1.2 through the stacked vlan you see the packets vanish. With ping -s 1468 192.168.1.2 everything seems ok. I have the impression that the stacked vlans show some problem with mtu handling inside the e1000 driver. Mtu is set to 1500 but because stacking tags uses 4 bytes more the packets cannot use the full mtu. Any ideas what happens here? The packet is being dropped because it is longer than the allowed frame size for 1500 MTU. check ethtool -S eth0 mine shows rx_long_length_errors: 169 which indicates that you need to change your mtu on the stacked interface to 1496, at which point after I did: ip l s eth1.4094.1 mtu 1496 on both sides of my connection, everything was working. I think in this case it is just a configuration problem. When you stack vlans you have to account for the extra inserted length someplace and that place is by reducing the MTU. I'd appreciate it in the future if you could use [EMAIL PROTECTED] or netdev@vger.kernel.org for support questions like this because I'm not the only one who can answer questions (and I might have been on vacation! :-) ) Jesse - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: e1000 and 802.1ad/stacked vlan tagging
Stephan von Krawczynski wrote: thank you for answering anyway. Though I think your answer covers only the obvious half of the problem. Indeed one might think that this solves the issue - as long as there are only linux kernels involved. Unfortunately my setup is a bit more complicated in terms of hardware. So I should have probably clarified the question this way: how do you configure the interface in a manner that packets with data length of 1500 get transferred, and not only 1496 ? I tried setting mtu 2000 and everything worked with the virtual device (both) mtu at 1500. If you are getting long_packet errors at the mtu settings you tried (you didn't mention which ones) then the hardware is dropping the packets due to being over 1522 bytes in length (including CRC). I tried enlarging both real-device and first vlan interface mtu but that does not work out. I really thought that the visible device setting of mtu=1500 should have worked out and that the driver (or some code in between) should have corrected the allowed frame size to reflect the actual setup, not? unfortunately I believe that your hardware MTU on the base interface MUST be adjusted in order to do stacked vlans because the vlan code doesn't fragment packets, it just inserts tags. The e1000 hardware is capable of inserting/stripping 1 level of tags without dropping overlong frames, but cannot seamlessly handle 1+n levels of inserted tags. Transmit, we don't care how long the frames are that are given to us (the driver doesn't enforce MTU on transmit) but on receive we have limited space so it is important that each frame fit into the allocated buffer (including CRC). Please try MTU 1508 on eth0 (base interface only), as that configuration worked for me. Jesse - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: e1000 and 802.1ad/stacked vlan tagging
Stephan von Krawczynski wrote: Hello Jesse, thank you for answering anyway. Though I think your answer covers only the obvious half of the problem. Indeed one might think that this solves the issue - as long as there are only linux kernels involved. Unfortunately my setup is a bit more complicated in terms of hardware. So I should have probably clarified the question this way: how do you configure the interface in a manner that packets with data length of 1500 get transferred, and not only 1496 ? I tried enlarging both real-device and first vlan interface mtu but that does not work out. I really thought that the visible device setting of mtu=1500 should have worked out and that the driver (or some code in between) should have corrected the allowed frame size to reflect the actual setup, not? Unless you are patching the VLAN code, stacked VLANs are not going to work anyway. Search the archives of the VLAN mailing list for reasons why..and at least a few patches that 'fix' the problem for a few types of uses. Ben - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
