Problem with a UDP server implements
Hi: I'm writing a UDP server and meet a problem the UDP server program is run on a box with single card but has multi ip: like eth0 10.0.0.1 eth0:1 10.0.0.2 eth0:2 11.0.0.1 I bind the server socket with INADDR_ANY when a client send a packet to 10.0.0.2(the eth0:1 's ip) the server can recieve the packet and reply, but the client can't recieve the server's response I use wireshark to capture the response packet and found that the server use 10.0.0.1(the eth0 's ip) as saddr in the response packet I expected it to be 10.0.0.2 but it's not my question : is there any way to let the UDP server relpy just use the ip it receieved the request ? It's : when a client send a request to 10.0.0.1(eth0); the server use 10.0.0.1 to response and another client send a request to 10.0.0.2(eth0:1); the server use 10.0.0.2 to response Thanks. 2011-10-15 jiangtao.jit
Hi! On 01:51 Sat 15 Oct , jiangtao.jit wrote:
Hi:
I'm writing a UDP server and meet a problem the UDP server program is run on a box with single card but has multi ip: like eth0 10.0.0.1 eth0:1 10.0.0.2 eth0:2 11.0.0.1
I bind the server socket with INADDR_ANY ... when a client send a request to 10.0.0.1(eth0); the server use 10.0.0.1 to response and another client send a request to 10.0.0.2(eth0:1); the server use 10.0.0.2 to response
Well, is seems there is neither a variant of recvfrom() which tells you your local address nor a variant of sendto() which allows you to specify your local address. I guess you have to call getaddrinfo() and create a socket for every address you want to bind to. If you want to stay single threaded you can switch them to nonblocking and use epoll to wait for packets. -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com
michi: 1. Is that to create two sockets and one bind to 10.0.0.1 the other bind to 10.0.0.2 then use epoll wait these two sockets ? 2. Is there any way to find out the turple like TCP then the UDP server can reply with exactly the ip it recieved the client's request ? Thanks. 2011/10/15 <michi1@michaelblizek.twilightparadox.com>:
Hi!
On 01:51 Sat 15 Oct , jiangtao.jit wrote:
Hi:
I'm writing a UDP server and meet a problem the UDP server program is run on a box with single card but has multi ip: like eth0 10.0.0.1 eth0:1 10.0.0.2 eth0:2 11.0.0.1
I bind the server socket with INADDR_ANY ... when a client send a request to 10.0.0.1(eth0); the server use 10.0.0.1 to response and another client send a request to 10.0.0.2(eth0:1); the server use 10.0.0.2 to response
Well, is seems there is neither a variant of recvfrom() which tells you your local address nor a variant of sendto() which allows you to specify your local address. I guess you have to call getaddrinfo() and create a socket for every address you want to bind to. If you want to stay single threaded you can switch them to nonblocking and use epoll to wait for packets.
-Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com
Hi! On 16:29 Sat 15 Oct , tao jiang wrote:
michi:
1. Is that to create two sockets and one bind to 10.0.0.1 the other bind to 10.0.0.2 then use epoll wait these two sockets ?
Yes, exactly.
2. Is there any way to find out the turple like TCP then the UDP server can reply with exactly the ip it recieved the client's request ?
You should receive the packet only on the socket which is bound to the address. You can save the bind address somewhere, so you know the local address. You will know the client address because it is passed back by recvfrom. -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com
michi: Thanks for your help. Much appreciated. 2011/10/15 <michi1@michaelblizek.twilightparadox.com>:
Hi!
On 16:29 Sat 15 Oct , tao jiang wrote:
michi:
1. Is that to create two sockets and one bind to 10.0.0.1 the other bind to 10.0.0.2 then use epoll wait these two sockets ?
Yes, exactly.
2. Is there any way to find out the turple like TCP then the UDP server can reply with exactly the ip it recieved the client's request ?
You should receive the packet only on the socket which is bound to the address. You can save the bind address somewhere, so you know the local address. You will know the client address because it is passed back by recvfrom.
-Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com
On Sam, 2011-10-15 at 01:51 +0800, jiangtao.jit wrote:
Hi:
I'm writing a UDP server and meet a problem the UDP server program is run on a box with single card but has multi ip: like eth0 10.0.0.1 eth0:1 10.0.0.2 eth0:2 11.0.0.1
I bind the server socket with INADDR_ANY
when a client send a packet to 10.0.0.2(the eth0:1 's ip) the server can recieve the packet and reply, but the client can't recieve the server's response I use wireshark to capture the response packet and found that the server use 10.0.0.1(the eth0 's ip) as saddr in the response packet I expected it to be 10.0.0.2 but it's not my question : is there any way to let the UDP server relpy just use the ip it receieved the request ? It's : when a client send a request to 10.0.0.1(eth0); the server use 10.0.0.1 to response and another client send a request to 10.0.0.2(eth0:1); the server use 10.0.0.2 to response
You can always build the complete raw packet (including the IP header) yourself. Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
Bernd: Is it to create a SOCK_RAW socket for receieve and send? Then is it means I have to parse the IP header and options if any? Will it cause performance problem, compare to SOCK_DGRAM? Thanks. 2011/10/15 Bernd Petrovitsch <bernd@petrovitsch.priv.at>:
On Sam, 2011-10-15 at 01:51 +0800, jiangtao.jit wrote:
Hi:
I'm writing a UDP server and meet a problem the UDP server program is run on a box with single card but has multi ip: like eth0 10.0.0.1 eth0:1 10.0.0.2 eth0:2 11.0.0.1
I bind the server socket with INADDR_ANY
when a client send a packet to 10.0.0.2(the eth0:1 's ip) the server can recieve the packet and reply, but the client can't recieve the server's response I use wireshark to capture the response packet and found that the server use 10.0.0.1(the eth0 's ip) as saddr in the response packet I expected it to be 10.0.0.2 but it's not my question : is there any way to let the UDP server relpy just use the ip it receieved the request ? It's : when a client send a request to 10.0.0.1(eth0); the server use 10.0.0.1 to response and another client send a request to 10.0.0.2(eth0:1); the server use 10.0.0.2 to response
You can always build the complete raw packet (including the IP header) yourself.
Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
On Die, 2011-10-18 at 07:26 +0800, tao jiang wrote: [....]
Is it to create a SOCK_RAW socket for receieve and send?
Only for sending. Search for sourcecode for `ping` - there are several around that show how to do it. You can use recvfrom() to get the senders address for each packet. [...]
Will it cause performance problem, compare to SOCK_DGRAM?
IMHO that won't measurably - either user-space constructs the UDP and IP header or the kernel does. And we talk about a few bytes only. [ Don't top-post. ] Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
Bernd: Thanks for your guide. But there is still a question if recvfrom() used, how to figure out the client's dest ip for reply ? i.e. on which ip the server receieved the request when construct the IP header, i don't know which saddr to fill in Thanks. 2011/10/18 Bernd Petrovitsch <bernd@petrovitsch.priv.at>:
On Die, 2011-10-18 at 07:26 +0800, tao jiang wrote: [....]
Is it to create a SOCK_RAW socket for receieve and send?
Only for sending. Search for sourcecode for `ping` - there are several around that show how to do it.
You can use recvfrom() to get the senders address for each packet.
[...]
Will it cause performance problem, compare to SOCK_DGRAM?
IMHO that won't measurably - either user-space constructs the UDP and IP header or the kernel does. And we talk about a few bytes only.
[ Don't top-post. ]
Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
Hi! On Die, 2011-10-18 at 22:48 +0800, tao jiang wrote: [...]
Thanks for your guide. But there is still a question if recvfrom() used, how to figure out the client's dest ip for reply ? i.e. on which ip the server receieved the request when construct the IP header, i don't know which saddr to fill in
Ooops, forgot that we need the destination address of the received packet too to construct the answer for it. Then yes, it seems that you would need the raw packet on the receiving side too. [ Full quote deelted ] Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
Bernd: Thanks again. 2011/10/19 Bernd Petrovitsch <bernd@petrovitsch.priv.at>:
Hi!
On Die, 2011-10-18 at 22:48 +0800, tao jiang wrote: [...]
Thanks for your guide. But there is still a question if recvfrom() used, how to figure out the client's dest ip for reply ? i.e. on which ip the server receieved the request when construct the IP header, i don't know which saddr to fill in
Ooops, forgot that we need the destination address of the received packet too to construct the answer for it. Then yes, it seems that you would need the raw packet on the receiving side too.
[ Full quote deelted ]
Bernd -- Bernd Petrovitsch Email : bernd@petrovitsch.priv.at LUGA : http://www.luga.at
participants (4)
-
Bernd Petrovitsch -
jiangtao.jit -
michi1＠michaelblizek.twilightparadox.com -
tao jiang