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Date:	Tue, 18 Feb 2014 14:14:09 -0800
From:	Vincent Li <vincent.mc.li@...il.com>
To:	Vincent Li <vincent.mc.li@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: socket bind to local address ::ffff:127.0.0.1 question

for my own education, and want to know where the code path for the
connect returns 'EHOSTUNREACH' in kernel, I grepped ''EHOSTUNREACH' in
./net directory and think  following might match the code path :

[root@...tos64-vm centos-6.2]# grep -r -w 'EHOSTUNREACH' net/*

net/ipv4/fib_semantics.c:               .error  = -EHOSTUNREACH,

net/ipv4/tcp_output.c:          return -EHOSTUNREACH; /* Routing
failure or similar. */ <------this one?


net/ipv4/ip_input.c:                    if (err == -EHOSTUNREACH)
net/ipv4/ip_output.c:   return -EHOSTUNREACH;
<------------------------------- or this one?

net/ipv4/tcp_ipv4.c:            err = EHOSTUNREACH;
net/ipv4/route.c:               case EHOSTUNREACH:
net/ipv4/route.c:       err = -EHOSTUNREACH;
net/ipv4/xfrm4_policy.c:                return -EHOSTUNREACH;

net/ipv6/route.c:                       err = -EHOSTUNREACH;
net/ipv6/xfrm6_policy.c:                return -EHOSTUNREACH;

net/xfrm/xfrm_output.c:                 err = -EHOSTUNREACH;
net/xfrm/xfrm_policy.c:                 err = -EHOSTUNREACH;

Could kernel expert confirm which code path the connect return comings from?

thanks

Vincent

On Mon, Feb 17, 2014 at 10:32 AM, Vincent Li <vincent.mc.li@...il.com> wrote:
> sorry to respond late, I don't have code access to the program and no
> sample code to reproduce the issue. the strace only shows connect and
> getsockname trace. so the trouble shooting is very limited. the kernel
> version is centos 6.2 based. (2.6.32*)
>
> the strace file is too large to paste here, so I extract out the
> relevant information I think related, the connect call finally returns
> ' EHOSTUNREACH (No route to host)'
>
> 6797  12:37:01.871842 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(46854), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151086333263900]) = 0
>
> 6797  12:37:01.872186 close(11)         = 0 <---here closed descriptor 11
>
> ------another new connection opened for discriptor 11, this is
> successfull one monitor instance----
>
> 6797  12:37:02.871031 fcntl64(11, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
>
> 6797  12:37:02.871121 fcntl64(11, F_SETFD, FD_CLOEXEC) = 0
>
> 6797  12:37:02.871229 connect(11, {sa_family=AF_INET6,
> sin6_port=htons(8180), inet_pton(AF_INET6, "::ffff:172.16.3.166",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=875638834}, 28) = -1
> EINPROGRESS (Operation now in progress)
>
> 6797  12:37:02.873006 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433145657494601756]) = 0
>
> 6797  12:37:02.876424 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151292491694108]) = 0
>
> 6797  12:37:02.878081 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151155052740636]) = 0
>
> 6797  12:37:02.878353 connect(11, {sa_family=AF_INET6,
> sin6_port=htons(8180), inet_pton(AF_INET6, "::ffff:172.16.3.166",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=875638834}, 28) = 0
>
> 6797  12:37:02.878467 getsockopt(11, SOL_TCP, TCP_MAXSEG,
> [700869393474651560], [4]) = 0
>
> 6797  12:37:02.878553 fcntl64(11, F_GETFL) = 0x802 (flags O_RDWR|O_NONBLOCK)
>
> 6797  12:37:02.878673 fcntl64(11, F_SETFL, O_RDWR|O_NONBLOCK) = 0
>
> 6797  12:37:02.878768 fcntl64(11, F_SETFD, FD_CLOEXEC) = 0
>
> 6797  12:37:02.878851 setsockopt(11, SOL_TCP, TCP_NODELAY, [1], 4) = 0
>
> 6797  12:37:02.880352 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151155052740636]) = 0
>
> 6797  12:37:02.880884 write(11, "GET /status HTTP/1.0\r\n\r\n", 24) =
> 24 <---monitor http request
>
> 6797  12:37:02.882551 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151155052740636]) = 0
>
> 6797  12:37:02.886150 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151292491694108]) = 0
>
> 6797  12:37:02.887843 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151086333263900]) = 0
>
> 6797  12:37:02.888096 read(11, "HTTP/1.1 200 OK\r\nServer:
> Apache-"..., 5120) = 3175 <----server response ok
>
> 6797  12:37:02.888214 read(11, "", 1945) = 0
>
> 6797  12:37:02.889833 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151086333263900]) = 0
>
> 6797  12:37:02.891532 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(33334), inet_pton(AF_INET6, "::ffff:172.16.17.161",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151086333263900]) = 0
>
> 6797  12:37:02.891896 close(11)         = 0 <-------this sucessfull
> monitor instance closed
>
> ------a failed monitor instance started on discriptor 11, no
> getsockopt and setsockopt traced-----------
>
> 6797  12:37:03.790155 fcntl64(11, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
>
> 6797  12:37:03.790237 fcntl64(11, F_SETFD, FD_CLOEXEC) = 0
>
> 6797  12:37:03.790342 connect(11, {sa_family=AF_INET6,
> sin6_port=htons(8180), inet_pton(AF_INET6, "::ffff:172.16.3.165",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=875638834}, 28) = -1
> EINPROGRESS (Operation now in progress)
>
> 6797  12:37:03.791998 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(45633), inet_pton(AF_INET6, "::ffff:127.0.0.1",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433145657494601756]) = 0
>
> 6797  12:37:06.796980 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(45633), inet_pton(AF_INET6, "::ffff:127.0.0.1",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151292491694108]) = 0
>
> 6797  12:37:06.798645 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(45633), inet_pton(AF_INET6, "::ffff:127.0.0.1",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
> [18433151155052740636]) = 0
>
> 6797  12:37:06.798919 connect(11, {sa_family=AF_INET6,
> sin6_port=htons(8180), inet_pton(AF_INET6, "::ffff:172.16.3.165",
> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=875638834}, 28) = -1
> EHOSTUNREACH (No route to host)
>
>
> 6797  12:37:06.800437 getsockname(11, {sa_family=AF_INET6,
> sin6_port=htons(45633), inet_pton(AF_INET6, "::", &sin6_addr),
> sin6_flowinfo=0, sin6_scope_id=0}, [18433150467857973276]) = 0
>
> 6797  12:37:06.800777 close(11)         = 0
>
> we have continuously ip route dump when the issue happend 'ip route
> get 172.16.3.165', there is always default route to 172.16.3.165 and
> the we also see the SYN packet going out on the wire sourcing from
> 127.0.0.1, so there is no layer 2 arp issue and no icmp error packet
> reported that is why I am looking for if there is potential kernel
> issue here.
>
>
>
>
>
>
>
>
>
>
>
>
> On Sat, Feb 15, 2014 at 9:10 AM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
>> On Wed, Feb 12, 2014 at 12:41:21PM -0800, Vincent Li wrote:
>>> we have a traffic path like <BIGIP monitor userland process on Linux>
>>> <------> router<------->pool/real server
>>>
>>> there is a  weird issue that intermittently, a socket is bound to
>>> loopback address '::ffff:127.0.0.1' which caused issue for us because
>>> remote end host can't SYN+ACK the SYN source from 127.0.0.1, strace
>>> the userland process shows:
>>>
>>> 6797  12:36:48.815296 connect(11, {sa_family=AF_INET6,
>>> sin6_port=htons(8180), inet_pton(AF_INET6, "::ffff:172.16.3.165",
>>> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=875638834}, 28) = -1
>>> EINPROGRESS (Operation now in progress)
>>
>> Have you checked the connect operation completed successfully in this
>> case? Error state would be interesting to see (SO_ERROR).
>>
>>> 6797  12:36:48.815464 gettimeofday({1391744208, 815499}, NULL) = 0
>>> 6797  12:36:48.815552 time(NULL)        = 1391744208
>>> 6797  12:36:48.815657 stat64("/etc/localtime", {st_mode=S_IFREG|0644,
>>> st_size=331, ...}) = 0
>>> ...................
>>> 6797  12:36:48.816948 getsockname(11, {sa_family=AF_INET6,
>>> sin6_port=htons(45621), inet_pton(AF_INET6, "::ffff:127.0.0.1",
>>> &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0},
>>> [18433145657494601756]) = 0
>>    ^^^
>> Urks!
>>
>> What kernel version are you using?
>>
>> Do you have a reproducer, sample code in C where this problem sometimes
>> happens or could you expand the strace listings a bit (maybe setsockopts,
>> bindv6only settings)?
>>
>> Also you seem to not initialize your struct sockaddr_in6 given to connect, as
>> the sin6_scope_id seems bogus (uninitialized memory?). But should not
>> matter with v4mapped addresses though.
>>
>> Greetings,
>>
>>   Hannes
>>
>>
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