Re: [Xen-devel] [PATCH] [XM-TEST] Use explicit (IP id==packet size) on hping2 tests to avoid problems with IP id==0

[Nivedita Singhvi <niv@xxxxxxxxxx>]

James Dykman wrote:
> We have run into some xm-test network test failures in the tests that use 
> hping2 that are caused by an IP id of 0:
> - hping2 uses a packet socket, so must do its own fragmentation when 
> sending messages >1500 bytes.
> - When fragmenting, hping2 uses the low byte of the PID as the IP id in 
> each of the fragmented IP headers.
> - The kernel will assign an IP id if it sees the IP id ==  0 in the header 
> that hping2 passes down 
>    (net/ipv4/raw.c:raw_send_hdrinc())
> So if the low byte of the PID is 0, every fragment will get assigned a 
> unique IP id by the kernel, and 
> reassembly will fail at the destination.
> Jim
> ----------------------------------
> Use explicit (IP id==packet size) on hping2 tests to avoid problems with 
> IP id==0
Jim, will this not be a cause potential corruption - if we have incoming
fragments belonging to different packets with the same ipid
there is no way for the reassembly code to distinguish them.
Checksum failures might catch some, but that is no guarantee of
safe delivery.

I realize the stuff may be getting serialized enough for now
that we don't run into the problem while testing - but a globally
unique ipid is necessary to avoid corruption in an
environment where fragments can get dropped or arrive out
of order. What am I missing?

thanks,
Nivedita


> Signed-off-by: Jim Dykman <dykman@xxxxxxxxxx>
>
> diff -r dc213d745642 
> tools/xm-test/tests/network/03_network_local_tcp_pos.py
> --- a/tools/xm-test/tests/network/03_network_local_tcp_pos.py   Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/03_network_local_tcp_pos.py   Thu May 18 
> 14:19:01 2006
> @@ -44,7 +44,7 @@
>      lofails=""
>      for size in trysizes:
>          out = console.runCmd("hping2 127.0.0.1 -E /dev/urandom -q -c 20 "
> -              + "--fast -d " + str(size))
> +              + "--fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              lofails += " " + str(size)
>
> @@ -54,7 +54,7 @@
>      ip = netdev.getNetDevIP()
>      for size in trysizes:
>          out = console.runCmd("hping2 " + ip + " -E /dev/urandom -q -c 20 
> "
> -              + "--fast -d "+ str(size))
> +              + "--fast -d "+ str(size) + " -N " + str(size))
>          if out["return"]:
>              eth0fails += " " + str(size)
>  except ConsoleError, e:
> diff -r dc213d745642 
> tools/xm-test/tests/network/04_network_local_udp_pos.py
> --- a/tools/xm-test/tests/network/04_network_local_udp_pos.py   Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/04_network_local_udp_pos.py   Thu May 18 
> 14:19:01 2006
> @@ -43,7 +43,7 @@
>      lofails=""
>      for size in trysizes:
>          out = console.runCmd("hping2 127.0.0.1 -E /dev/urandom -2 -q -c 
> 20 "
> -              + "--fast -d " + str(size))
> +              + "--fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              lofails += " " + str(size)
>              print out["output"]
> @@ -54,7 +54,7 @@
>      ip = netdev.getNetDevIP()
>      for size in trysizes:
>          out = console.runCmd("hping2 " + ip + " -E /dev/urandom -2 -q -c 
> 20 "
> -              + "--fast -d " + str(size))
> +              + "--fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              eth0fails += " " + str(size)
>              print out["output"]
> diff -r dc213d745642 
> tools/xm-test/tests/network/06_network_dom0_tcp_pos.py 
> --- a/tools/xm-test/tests/network/06_network_dom0_tcp_pos.py    Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/06_network_dom0_tcp_pos.py    Thu May 18 
> 14:19:01 2006
> @@ -44,7 +44,7 @@
>      dom0ip = netdev.getDom0AliasIP()
>      for size in trysizes:
>          out = console.runCmd("hping2 " + dom0ip + " -E /dev/urandom -q -c 
> 20 "
> -              + "--fast -d " + str(size))
> +              + "--fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              fails += " " + str(size)
>              print out["output"]
> diff -r dc213d745642 
> tools/xm-test/tests/network/07_network_dom0_udp_pos.py
> --- a/tools/xm-test/tests/network/07_network_dom0_udp_pos.py    Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/07_network_dom0_udp_pos.py    Thu May 18 
> 14:19:01 2006
> @@ -43,7 +43,7 @@
>      dom0ip = netdev.getDom0AliasIP()
>      for size in trysizes:
>          out = console.runCmd("hping2 " + dom0ip + " -E /dev/urandom -2 -q 
> -c 20"
> -             + " --fast -d " + str(size))
> +             + " --fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              fails += " " + str(size)
>              print out["output"]
> diff -r dc213d745642 
> tools/xm-test/tests/network/12_network_domU_tcp_pos.py
> --- a/tools/xm-test/tests/network/12_network_domU_tcp_pos.py    Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/12_network_domU_tcp_pos.py    Thu May 18 
> 14:19:01 2006
> @@ -50,7 +50,7 @@
>      ip2 = dst_netdev.getNetDevIP()
>      for size in pingsizes:
>          out = src_console.runCmd("hping2 " + ip2 + " -E /dev/urandom -q 
> -c 20 "
> -              + "--fast -d " + str(size))
> +              + "--fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              fails += " " + str(size)
>              print out["output"]
> diff -r dc213d745642 
> tools/xm-test/tests/network/13_network_domU_udp_pos.py
> --- a/tools/xm-test/tests/network/13_network_domU_udp_pos.py    Mon May 15 
> 15:32:09 2006
> +++ b/tools/xm-test/tests/network/13_network_domU_udp_pos.py    Thu May 18 
> 14:19:01 2006
> @@ -50,7 +50,7 @@
>      ip2 = dst_netdev.getNetDevIP()
>      for size in pingsizes:
>          out = src_console.runCmd("hping2 " + ip2 + " -E /dev/urandom -2 
> -q "
> -              + "-c 20 --fast -d " + str(size))
> +              + "-c 20 --fast -d " + str(size) + " -N " + str(size))
>          if out["return"]:
>              fails += " " + str(size)
>              print out["output"]
>
>
>
>
>
>
> ------------------------------------------------------------------------
>
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