rohc team mailing list archive

[Didier Barvaux <didier.barvaux@xxxxxxxxxxxxxxxxxxxx>]

Hi Ramya,


>           I downloaded the ROHC-1.2.0 package from launchpat.net. I
> installed the
> packages(automake,m4,autoconf,bison,flex,perl,libtool,help2man,texinfo,gcc,libpcap,gawk)
> and compiled the package as follows:
> step 1: ./autogen.sh --prefix=/usr/local/bin
> step 2: make all
> step 3: make install
> 
> [...]
> 
> Is this right?

Yes, the commands are OK.


> Next, I executed the command
> 
> ip link set eth0:rohc0
>  ip -4 addr add 10.0.0.1/24 dev eth0:rohc0

That is correct too.


> Next tried to capture those packets in another system using
> tcpdump -v -x -i eth0:rohc0
> 
> The output is as follows:
> tcpdump: listening on eth0:rohc0, link-type EN10MB (Ethernet),
> capture size 96 bytes
> 11:34:35.836636 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF],
> proto ICMP (1), length 108) 192.168.1.3 > 192.168.1.8: ICMP echo
> request, id 41486, seq 37, length 88
>     0x0000:  4500 006c 0000 4000 4001 b735 c0a8 0103
>     0x0010:  c0a8 0108 0800 6b62 a20e 0025 a16b df4b
>     0x0020:  4a7c 0d00 0809 0a0b 0c0d 0e0f 1011 1213
>     0x0030:  1415 1617 1819 1a1b 1c1d 1e1f 2021 2223
>     0x0040:  2425 2627 2829 2a2b 2c2d 2e2f 3031 3233
>     0x0050:  3435
> [...]
> From the logs it can be seen that there is no compression happening.
> Please point me in the right direction.

ROHC compression is happening but you can not see it with a tcpdump
command on the interface "eth0:rohc0". On this interface, you can only
capture the uncompressed packets before they went to the ROHC compressor
and the decompressed packets generated by the ROHC decompressor. The
ROHC packets can be captured on the underlying network interface (it
seems to be the "eth0" interface for you). The ROHC packets are
transmitted in UDP datagrams with port 5000. The UDP payload is a
sequence number followed by the compressed ROHC data.


Regards,

Didier Barvaux
Viveris Technologies
http://www.tech.viveris.com/opensource/