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Re: tun/tap issue

cc'ing the cl-mirage mailing list, in case anyone there has anything to 

(i'm not sure whether udita is on the list, so please keep her cc'd. if someone 
could add her to the list, that'd be great.)

for the list-- udita is an intern from IIIT who's helping me with some 
homework/openflow/mirage related things. her current task is to try to pin down 
the effects and then the cause of the bug that i believed i was seeing trying 
to use mirage networking on linux. (i mailed about this problem previously.)

On 8 May 2013, at 16:57, Udita Gangwal wrote:

> Could you tell me what problem were you exactly facing with the ocaml-tuntap 
> in Linux? You said that the packets were somehow getting  lost somewhere. 
> Could you please let me know the exact scenario?

when i compiled and built mirage-www on linux using 4.00.1+mirage-unix (and 
3.12.1+mirage-unix-direct), i find that i can run the resulting binary, 
everything appears to work, i can ping the address it claims using the tuntap 
code ( but when i try to "telnet 80" to connect to the web 
server that should be running, it doesn't connect. when i ran tcpdumps on all 
the interfaces, it appeared that, although the route table entry should have 
been sending all traffic directed to to the tap0 interface, in fact 
the tcpdumps showed the TCP SYN packets were being sent to the lo (loopback) 

all of this worked fine for me on OSX, hence my hypothesis was that this was 
due to some bug in how the tuntap and/or netfilter apis were being used. iirc 
ping is handled on a different path in the kernel, hence was working ok.

vincent has since extracted the tuntap functionality from mirage-net into its 
own library, ocaml-tuntap. the suggestion was to try writing a couple of simple 
test apps, perhaps one using ping and one that just runs a simple tcp server of 
some kind that you can try to connect to (make it an echo server if you're 
feeling fancy :)  if both of those "Just Work" for you on linux, then it would 
seem that this is my problem alone. if either doesn't work, then we can start 
to track down the bug. either way, having a couple of simple examples for 
ocaml-tuntap will be useful :)

anil, vincent -- anything to add?



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