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George Tasioulis's questions

Martin Hope
George Tasioulis
Asked: 2022-01-08 14:56:35 +0800 CST
  • 0

I have two servers in different locations. Each server has an eth0 with a public IP (internet accessible) and an eth1 with a private IP connected to the internal network.

Server A

eth0: 1.2.3.4 (public IP)
eth1: 10.0.0.10/24

Server B

eth0: 5.6.7.8 (public IP)
eth1: 10.10.1.10/24

I have a GRE tunnel between the two servers, created like this:
Server A

ip tunnel add gre1 mode gre remote 5.6.7.8 local 1.2.3.4 ttl 255
ip link set gre1 up
ip addr add 10.128.128.1/24 dev gre1

Server B

ip tunnel add gre1 mode gre remote 1.2.3.4 local 5.6.7.8 ttl 255
ip link set gre1 up
ip addr add 10.128.128.2/24 dev gre1

Now the goal here is to be able to access the other side's private network from each server. So from Server A I want to be able to access the devices at 10.10.1.0/24, and from Server B I want to be able to access the devices at 10.0.0.0/24.

I tried adding ip route add 10.10.1.0/24 dev gre1 on Server A and ip route add 10.0.0.0/24 dev gre1 on Server B, but it didn't help.

What am I missing? Do I need to use source route tables?

Thanks in advance,
George

iptables route tunnel gre
Martin Hope
George Tasioulis
Asked: 2012-10-14 08:02:57 +0800 CST
  • 2

I have a "development" KVM server here at the office, setup in a bridged networking setup with a few KVM guests running on it. For each KVM guest a virtual interface is created on the node with the name kvm[id].0 e.g. kvm126.0 when the guest boots. Yesterday I was playing around and wanted to see how I could nullroute a KVM guest in case I needed to.

So I tried route add ip_address reject which had no effect, as no effect had route add ip_address gw 127.0.0.1 lo or ip route add blackhole ip_address/32. Since it's a bridged network setup, I get why the above didn't work.

Next try was with iptables; I tried

iptables -A INPUT -s ip_address -j DROP
iptables -A FORWARD -s ip_address -j DROP

which did the trick, I couldn't ping the KVM guest anymore.

Now the thing is that if I were a malicious user, I would start trying other neighboring IPs until I find one that doesn't conflict with another guest and statically assign it to my VPS.

So what I would like to know is, if there's a way to block traffic from this guest's particular interface, no matter what IP he has managed to configure his guest machine with.

linux
Martin Hope
George Tasioulis
Asked: 2012-09-24 17:41:57 +0800 CST
  • 4

I'm having a weird issue with a vBulletin forum, on a 2х Xeon E5645 w/ 16GB RAM CentOS 6.3 x86_64 web server with cPanel and LiteSpeed; It takes too long to start loading...

When I tested it with webpagetest.org I saw that for every request there's a 3 second "Initial connection" delay, which I don't know why is happening. Here's a screenshot: enter image description here

CPU Load is between 0.03 and 0.05, I've got several GB of free RAM, practical no I/O activity, and this delay can occur even with only one visitor on the forum.

Where do you suggest I start searching? What could be the reason for this kind of delay? I don't think it's the webserver, or the forum because there's another website on the server (total 2 sites) which is WordPress based, and has exactly the same issue with the 3 second initial connection delay. I believe it's OS related, but need a clue on where to start looking.

linux
Martin Hope
George Tasioulis
Asked: 2012-08-29 14:27:25 +0800 CST
  • 5

I have a CentOS server, configured with 4 consecutive IPs:
eth0 5.x.x.251
eth0:0 5.x.x.252
eth0:1 5.x.x.253
eth0:2 5.x.x.254

The problem is that all traffic goes out to the internet with eth0:0 (5.x.x.252) as the source IP, instead of eth0.
# curl ifconfig.me
5.x.x.252

How can I fix this, so that all traffic goes out via eth0, ie my main IP?

PS: My server is VPS running on a Xen dom0, the latter being configured in routed mode networking.

Thanks in advance!

Server configuration 

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:x:x:x:x:AE  
          inet addr:5.x.x.251  Bcast:5.x.x.255  Mask:255.255.255.255
          inet6 addr: fe80::x:x:x:x/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:14675569 errors:0 dropped:0 overruns:0 frame:0
          TX packets:9463227 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:4122016502 (3.8 GiB)  TX bytes:25959110751 (24.1 GiB)
          Interrupt:23 

eth0:0    Link encap:Ethernet  HWaddr 00:x:x:x:x:AE   
          inet addr:5.x.x.252  Bcast:5.x.x.255  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:23 

eth0:1    Link encap:Ethernet  HWaddr 00:x:x:x:x:AE  
          inet addr:5.x.x.253  Bcast:5.x.x.255  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:23 

eth0:2    Link encap:Ethernet  HWaddr 00:x:x:x:x:AE  
          inet addr:5.x.x.254  Bcast:5.x.x.255  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:23  

# cat /etc/hosts
127.0.0.1       localhost.localdomain localhost
5.x.x.251       [fqdn] [hostname]

# cat ifcfg-eth0
DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=5.x.x.251
NETMASK=255.255.255.224
SCOPE="peer 5.x.y.82"

# cat ifcfg-eth0:0
DEVICE=eth0:0
BOOTPROTO=static
ONBOOT=yes
IPADDR=5.x.x.252
NETMASK=255.255.255.224

# cat route-eth0 
ADDRESS0=0.0.0.0
NETMASK0=0.0.0.0
GATEWAY0=5.x.y.82

# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
5.x.y.82        0.0.0.0         255.255.255.255 UH        0 0          0 eth0
5.x.x.224       0.0.0.0         255.255.255.224 U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
0.0.0.0         5.x.y.82        0.0.0.0         UG        0 0          0 eth0

Update 29 August 2012
When I run /etc/init.d/network restart I get an RTNETLINK answers: File exists error, which leads me to believe that there's another route to another network using the default gateway, as seen here.

# /etc/init.d/network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  RTNETLINK answers: File exists
                                                           [  OK  ]

The sure thing is that when I first delete ip route del default via 5.x.y.82 dev eth0 and then add it again with the .251 IP, everything works as expected.
Is there any way to add a route del command either to the ifcfg-eth0 or the route-eth0 files? I can see that this can be done with pre-up ip addr del ... on Debian (more info), but what about CentOS?

linux
Martin Hope
George Tasioulis
Asked: 2012-08-20 00:15:53 +0800 CST
  • -1

I have a mysqldump file in which I want to replace the following text <a href="/tag/ with <a href="http://www.mydomain.com/tag/ but can't find a way to correctly escape all special characters.

I'm using the following command (+ a few other variants)
cat wordpress_posts.sql | sed 's%/<a href="\/\tag\/\/<a href="\http:/\/\www.mydomain.com/\tag/\/%g' > wordpress_posts_new.sql
but it's not working.

Can anybody help?

Update 1: Turns out that the source string in the mysqldump isn't <a href="/tag/ but <a href=\"/tag/ (note the extra backslash after the equal symbol)
Here's a pastebin of one line of the SQL file which contains the string I want to replace: http://pastebin.com/8G5mcxpJ

I tried all 3 suggested versions of the sed command, but none would replace the above string with <a href=\"http://www.mydomain.com/tag/ (yes I added the backslash after the equal symbol)

linux
Martin Hope
George Tasioulis
Asked: 2012-03-21 17:25:23 +0800 CST
  • 3

I'm running a Xen based VM with CentOS 5, and my hosting provider pushes kernel version 2.6.37.6 from the host machine (so no pv-grub).

[root@dev ~]# uname -r
2.6.37.6

I'm trying to install the R1Soft agent, and I needed to build the hcpdriver module for it. Unfortunatelly yum install kernel-devel or yum install kernel-xen-devel didn't do the trick when I attempted to install the kernel headers needed to build the module (and i'm guessing it has to do with the fact that my hosting provider uses a custom kernel).

So I went ahead and downloaded the kernel from kernel.org, extracted it to /usr/src/ and ran:

zcat /proc/config.gz > .config
make oldconfig && make modules_prepare

Now that I had the kernel headers I built the hcpdriver module, but when I tried to modprobe/insmod it, I was getting the following error in dmesg

hcpdriver: no symbol version for module_layout

I googled the error and found some hints about vermagic. But my newly built module has the same vermagic as the previous module provided by my hosting provider (which apparently suffers from some kind of a bug and R1Soft support asked me to compile a newer version).

Here's the old -buggy- one (provided by my host):
[root@dev r1soft]# modinfo hcpdriver.o
filename: hcpdriver.o
version: 4.1.1 build 13785
license: Proprietary
description: Linux Hot Copy Driver
author: Michael Brumlow
depends:
vermagic: 2.6.37.6 SMP mod_unload modversions

and here's the new one I've build based on the newly compiled kernel headers:
[root@dev r1soft]# modinfo hcpdriver-cki-2.6.37.6.ko
filename: hcpdriver-cki-2.6.37.6.ko
version: 4.2.1 build 16433
license: Proprietary
description: Linux Hot Copy Driver
author: Michael Brumlow
depends:
vermagic: 2.6.37.6 SMP mod_unload modversions

As you can see vermagic is extactly the same. Problem is that the first module runs fine when I insmod it, but the second one doesn't.

Anybody ever had some kind of similar issue? It's the first time I built the kernel headers on my own, so I'm not quite sure if the process I used was the correct one in this case. Is there anything else I could try?

Update 1
I did the process from scratch again, redownloaded the tar.gz from kernel.org, untarred it into /usr/src/kernels and then ran:

zcat /proc/config.gz > .config
make
make modules_install && make headers_install

everything completed w/o errors.

then I ran:
r1soft-setup --get-module --no-binary
which also completed w/o errors, but now when I try to insmod the module, dmesg reports:
hcpdriver: disagrees about version of symbol __memcpy
hcpdriver: Unknown symbol __memcpy (err -22)

Thanks in advance, George

centos kernel compilation r1soft