?
Solved

Debian Linix GRE protocol forwarding

Posted on 2007-03-18
6
Medium Priority
?
2,992 Views
Last Modified: 2013-12-06
I'm using tcpdump to see if gre protocol is forwarding properly from my Debian linux box.

Here is the command I'm using
tcpdump -i eth0 proto 47 > /root/dump.txt
But the log file is empty I'm thinking because the protocol isn't even coming in, right?
When I look for protocol 6 (tcp) it fills up as I try and pptp in.  Any ideas?  Should I be seeing the gre protocol coming in?
0
Comment
Question by:MainStaySolutions
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
  • 2
6 Comments
 
LVL 8

Expert Comment

by:frashii
ID: 18855625
You might want to check to see that you are monitoring the correct interface... When I ran the following command on eth0, I got no packets... but when I ran it on ppp0 I did.

Do an ifconfig and see if there are other interfaces.

firewall:/root # tcpdump -i ppp0 proto 47
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on ppp0, link-type LINUX_SLL (Linux cooked), capture size 96 bytes
20:15:34.259140 IP xxxx.dyndns.org > xxxx.nwc.acsalaska.net: call 1039 ack 4294967295 no-payload
20:15:34.280656 IP xxx.dyndns.org > xxxx.nwc.acsalaska.net: call 1039 seq 0 gre-ppp-payload

2 packets captured
3 packets received by filter
0 packets dropped by kernel

firewall:/root # tcpdump -i eth0 proto 47
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes

0 packets captured
0 packets received by filter
0 packets dropped by kernel
0
 
LVL 8

Expert Comment

by:frashii
ID: 19006443
*ping* Did monitoring the ppp0 (or other encapsulated interface) show the GRE packets ?
0
 

Author Comment

by:MainStaySolutions
ID: 20728161
No it didnt.
0
Containers & Docker to Create a Powerful Team

Containers are an incredibly powerful technology that can provide you and/or your engineering team with huge productivity gains. Using containers, you can deploy, back up, replicate, and move apps and their dependencies quickly and easily.

 
LVL 19

Expert Comment

by:http:// thevpn.guru
ID: 20728231
try

iptables -A OUPUT -p tcp --dport 47 -j LOG
iptables -A FORWARD -p tcp --dport 47 -j LOG
iptables -A INPUT -p tcp --dport 47 -j LOG

or UDP ..and then
tail -f /var/log/syslog and you will see the packets being logged if they are incoming/outgoing or being forwarded by the system
0
 

Author Comment

by:MainStaySolutions
ID: 20733771
Thanks for the reply.  Interesting, I'm not seeing anything in the log files as I try to vpn through it.  I'm assuming that it means gre isn't passing through.
0
 
LVL 19

Accepted Solution

by:
http:// thevpn.guru earned 750 total points
ID: 20733797
Not necessarily in VPN is your traffic encrypted ?
0

Featured Post

The Orion Papers

Are you interested in becoming an AWS Certified Solutions Architect?

Discover a new interactive way of training for the exam.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Setting up Secure Ubuntu server on VMware 1.      Insert the Ubuntu Server distribution CD or attach the ISO of the CD which is in the “Datastore”. Note that it is important to install the x64 edition on servers, not the X86 editions. 2.      Power on th…
1. Introduction As many people are interested in Linux but not as many are interested or knowledgeable (enough) to install Linux on their system, here is a safe way to try out Linux on your existing (Windows) system. The idea is that you insta…
Learn how to get help with Linux/Unix bash shell commands. Use help to read help documents for built in bash shell commands.: Use man to interface with the online reference manuals for shell commands.: Use man to search man pages for unknown command…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
Suggested Courses
Course of the Month9 days, 17 hours left to enroll

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question