stv0g/netplika
1
0
Fork 0
Code Issues Pull requests Releases Wiki Activity

updated README

Browse source
This commit is contained in:
Steffen Vogel 2015-07-22 23:35:15 +02:00
parent f485b1874f
commit 948c279923
1 changed files with 15 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
README.md
View file

@ -55,8 +55,8 @@ At least the first three fields have to be given. The remaining ones are optiona
To apply the network emulation only to a limit stream of packets, you can use the `mark` tool.
./netem -m 0xCD dist load < measurements.dat
sudo LD_PRELOAD=${PWD}/mark.so MARK=0xCD ping google.de
./netem -m 0xBABE dist load < measurements.dat
sudo LD_PRELOAD=${PWD}/mark.so MARK=0xBABE netcat google.de 80
This tool uses the dynamic linker to hook into the `socket()` wrapper-function of libc (see `mark.c`).
Usually, the hook will simply call the original `socket(2)` syscall for non-AF_NET sockets.
@ -64,9 +64,18 @@ But for AF_INET sockets, the hook will additionally call `setsockopt(sd, SOL_SOC
Later on, the `netem` tool will use combination of the classfull `prio` qdisc and the `fw` classifier to limit the network emulation only to the _marked_ application (see use case 5, below).
*Note:* Please make sure the specify the environmental variables after the sudo command!
This is necessary, as `ping` is a SUID program.
The dynamic linker strips certain enviromental variables (as `LD_PRELOAD`) for security reasons!
*Note:* There are two pittfalls when using this approach:
- Make sure to specify the environmental variables after the sudo command! This is necessary, as `ping` is a SUID program. The dynamic linker strips certain enviromental variables (as `LD_PRELOAD`) for security reasons when privileges are elevated.
- Setting the packet mark requires CAP_NET_ADMIN privs. Therefore you must start the application as root. Unfortunately, some applications also drop those privs quite early (ping is an example which luckily has an `-m` option).
Alternatively you can set the mark using netfilter:
iptables -t mangle -I OUTPUT -d 8.8.8.8 --set-mark 0xBABE -j MARK
Or, the `tc-cgroup.sh` script which uses a special priority for a certain cgroup:
./tc-cgroup ping google.de
###### Use case 5: Show the current Traffic Controller setup
@ -167,4 +176,4 @@ This program is free software: you can redistribute it and/or modify it under th
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.