Hi, On Wed, Nov 30, 2011 at 10:06 AM, Thomas De Schampheleire <[email protected]> wrote: > On Wed, Nov 30, 2011 at 8:52 AM, Jiri Pirko <[email protected]> wrote: >> Tue, Nov 29, 2011 at 09:35:00PM CET, [email protected] wrote: >>>Le 29/11/2011 14:38, Thomas De Schampheleire a écrit : >>>>Hi, >>>> >>>>I'm seeing incorrect tcpdump output in the following scenario: >>>> >>>>* ethernet bonding enabled in the kernel, and a single network >>>>interface (eth0) added as slave >>>>* bonding mode was set to broadcast, but I don't think this matters >>>>* VLAN added to the bond0 network interface >>>>* ip address set on the vlan interface (bond0.1234) >>>>* tcpdump capturing full packets (-xx or even -x) on the eth0 interface >>>> >>>>Then, when pinging from another machine to this ip address, the ping >>>>reply packets shown by tcpdump incorrectly have a double VLAN tag. >>>>However, what really appears on the wire is correct: a single VLAN >>>>tag. >>> >>>Copied netdev, because bonding and vlan developers are there. >>> >>>Jiri, don't you think this might be related to the work you have done >>>to make non-hw-accel rx path similar to hw-accel? >> >> I do not think so. The changes you are reffering to are unrelated to tx >> path (where this issue has most probably roots in) >> >>> >>> Nicolas. >>> >>>> >>>>Here is the output from tcpdump: >>>># /tmp/tcpdump -i eth0 -xx >> >> What hw is this? > > This is on a Freescale P4080 DPA mac (fsl,p4080-fman-1g-mac). > >> >>>>tcpdump: verbose output suppressed, use -v or -vv for full protocol decode >>>>listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes >>>>01:04:04.607880 IP 192.168.1.2> 192.168.1.1: ICMP echo request, id 26933, >>>>seq 4 >>>>16, length 64 >>>> 0x0000: 0600 0000 0020 0600 0000 0020 8100 0ffe >>>> 0x0010: 0800 4500 0054 0000 4000 4001 b755 c0a8 >>>> 0x0020: 0102 c0a8 0101 0800 98d7 6935 01a0 e528 >>>> 0x0030: 0f2a 0000 0000 0000 0000 0000 0000 0000 >>>> 0x0040: 0000 0000 0000 0000 0000 0000 0000 0000 >>>> 0x0050: 0000 0000 0000 0000 0000 0000 0000 0000 >>>> 0x0060: 0000 0000 0000 >>>>01:04:04.607889 IP 192.168.1.1> 192.168.1.2: ICMP echo reply, id 26933, >>>>seq 416 >>>>, length 64 >>>> 0x0000: 0600 0000 0020 0600 0000 0020 8100 0ffe >>>> 0x0010: 8100 0ffe 0800 4500 0054 cc07 0000 4001<-------- >>>>extra VLAN header at 0x10 >>>> 0x0020: 2b4e c0a8 0101 c0a8 0102 0000 a0d7 6935 >>>> 0x0030: 01a0 e528 0f2a 0000 0000 0000 0000 0000 >>>> 0x0040: 0000 0000 0000 0000 0000 0000 0000 0000 >>>> 0x0050: 0000 0000 0000 0000 0000 0000 0000 0000 >>>> 0x0060: 0000 0000 0000 0000 0000 >>>> >>>> >>>>Initial debugging showed that the addition of the extra VLAN header >>>>takes place in function pcap_read_linux_mmap() of libpcap, in the >>>>following snippet: >>>> >>>>#ifdef HAVE_TPACKET2 >>>> if (handle->md.tp_version == TPACKET_V2&& >>>> h.h2->tp_vlan_tci&& >>>> tp_snaplen>= 2 * ETH_ALEN) { >>>> struct vlan_tag *tag; >>>> >>>> bp -= VLAN_TAG_LEN; >>>> memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN); >>>> >>>> tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN); >>>> tag->vlan_tpid = htons(ETH_P_8021Q); >>>> tag->vlan_tci = htons(h.h2->tp_vlan_tci); >>>> >>>> pcaphdr.caplen += VLAN_TAG_LEN; >>>> pcaphdr.len += VLAN_TAG_LEN; >>>> } >>>>#endif >> >> I haven't look into this code yet, but where's the code which does the >> first header inclusion? > > I would assume this is done by the VLAN layer. This is a ping reply > originating from the icmp code, passing down to the vlan layer, then > to the ethernet bonding layer, and then to the hardware. But before > this is passed to hardware, libpcap captures the packet. > > I haven't debugged that part, though, so I can't give you a direct > pointer to the code that does it. > >> >> >>>> >>>>Upon entry of this code, the packet in bp already contains a VLAN header. >>>> >>>>It's unclear to me where the problem lies exactly. I suspect it has >>>>something to do with the ethernet bonding layer indicating it has >>>>hardware vlan tagging support, while it does already fill in the vlan >>>>header, and libpcap being confused by this. >>>> >>>>As mentioned previously, the packets on the wire are correct, and this >>>>is purely a capturing problem. >>>> >
Does anyone have an idea on how this is supposed to work and why the extra header gets inserted? Thanks, Thomas - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
