How to create reverse DNS record in bind?

How to create reverse DNS record in bind :

Used Environment : RHEL 6

Steps followed :

1. Add following lines in /etc/named.conf :

---------
zone "0.168.192.in-addr.arpa" IN {
type master;
file "0.168.192.in-addr.arpa";
allow-update { none; };
};
---------

2. Create zone for this reverse record :

-------------------
$cat /var/named/0.168.192.in-addr.arpa

$TTL 600
@ IN SOA ns1.example.com. host.example.com. (
2012013001 ;Serial Number
86400 ;refresh
7200 ;retry
3600000 ;expire
86400 ;minimum

)

0.168.192.in-addr.arpa. IN NS ns1.example.com.
0.168.192.in-addr.arpa. IN NS ns2.example.com.
201 IN PTR example.com.
------------------

Testing :

-----------------------
$dig -x 192.168.0.201 @localhost

; <<>> DiG 9.7.3-P3-RedHat-9.7.3-8.P3.el6_2.2 <<>> -x 192.168.0.201 @localhost
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17992
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

;; QUESTION SECTION:
;201.0.168.192.in-addr.arpa. IN PTR

;; ANSWER SECTION:
201.0.168.192.in-addr.arpa. 600 IN PTR example.com.

;; AUTHORITY SECTION:
0.168.192.in-addr.arpa. 600 IN NS ns2.example.com.
0.168.192.in-addr.arpa. 600 IN NS ns1.example.com.

;; ADDITIONAL SECTION:
ns1.example.com. 86400 IN A 192.168.0.201
ns2.example.com. 86400 IN A 192.168.40.34

;; Query time: 0 msec
;; SERVER: ::1#53(::1)
;; WHEN: Wed Feb 22 15:00:32 2012
;; MSG SIZE rcvd: 137
---------------------------

DB of the zone example.com looks like :

--------------
$cat example.com
$TTL 24h

;
; zone data file
; comments can appear on any line after a semi-colon
;
example.com. IN SOA ns1.example.com. root.mail.example.com. (
2012013001 ; last updated January 30th,2012, once
24h
2h
4w
4d )

example.com. IN NS ns1.example.com.
example.com. IN NS ns2.example.com.
example.com. IN A 192.168.0.201
mail.example.com. IN A 192.168.0.201
ns1.example.com. IN A 192.168.0.201
ns2.example.com. IN A 192.168.40.34
www.example.com. IN CNAME example.com.
wwww.example.com. IN CNAME example.com.
ww.example.com. IN CNAME example.com.
example.com. IN MX 0 mail.example.com.

--------------

Read More

Which command will provide IO details of all processes in the system?

You can execute following command to get the details :

$ for i in {1..65353}; do if [ -f /proc/$i/io ] ; then echo "---------------------------------------------------"; echo "Process name :" ; cat /proc/$i/cmdline; echo "PID : $i" ; echo "IO Details:" ; cat /proc/$i/io ; fi; done

Read More

How to locally generate CA certificate and server - client certificate using CA on linux ?

Creating certification authority :

$cd /etc/newcerts
$openssl genrsa 2048 > ca-key.pem
$openssl req -new -x509 -nodes -days 1000 -key ca-key.pem > ca-cert.pem

NOTE: Last command will ask for details of certificate provider. So, provide short names

Creating certificate for server using above CA certificate :

$openssl req -newkey rsa:2048 -days 1000 -nodes -keyout server-key.pem > server-req.pem
$openssl x509 -req -in server-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 > server-cert.pem

NOTE: First command may ask for a password. Don't provide it. Just press enter key for two times.

Creating certificate for client using above CA certificate(similar like server) :

$openssl req -newkey rsa:2048 -days 1000 -nodes -keyout client-key.pem > client-req.pem .
$openssl x509 -req -in client-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 > client-cert.pem

NOTE : Provide details of client owner who will contact server. Short names may be same

Now client will contact to server using client-cert.pem and server will consult it its server-cert.pem and approve encryption.

Note that I have used same CA to generate cert for server as well as for client.

Read More

How to install mysql and configure SSL with it?

* How to install mysql and configure SSL with it?
* Received following error while I locally try to connect to mysql server over SSL.

[root@]# mysql --ssl-cert=/var/lib/mysql/openssl-md5/ca-cert.pem --ssl-key=/var/lib/mysql/openssl-md5/client-key.pem --ssl-cert=/var/lib/mysql/openssl-md5/client-cert.pem -u root -p -v -v -v

Enter password:

ERROR 2026 (HY000): SSL connection error

My used environment

* Red Hat Enterprise Linux 5.7

Required packages :

* perl-DBD-MySQL-3.0007-2.el5
perl-DBI-1.52-2.el5
mysql-server-5.0.77-4.el5_6.6
mysql-5.0.77-4.el5_6.6
mysql-5.0.77-4.el5_6.6

Resolution

1. Download all mysql related packages or use yum command to install the packages. You can use "rpm -ivh " to install them manually.
2. Start mysql.
4. Change mysql root password

Example :

[root@ /]# rpm -ivh perl-DBI-1.52-2.el5.x86_64.rpm

warning: perl-DBI-1.52-2.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186

Preparing... ########################################### [100%]

1:perl-DBI ########################################### [100%]

[root@/]# rpm -ivh mysql-5.0.77-4.el5_6.6.i386.rpm << This is needed on 64 bit os

warning: mysql-5.0.77-4.el5_6.6.i386.rpm: Header V3 DSA signature: NOKEY, key ID 37017186

Preparing... ########################################### [100%]

1:mysql ########################################### [100%]

[root@ /]# rpm -ivh mysql-5.0.77-4.el5_6.6.x86_64.rpm <<

warning: mysql-5.0.77-4.el5_6.6.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186

Preparing... ########################################### [100%]

1:mysql ########################################### [100%]

[root@ /]#

[root@ /]# rpm -ivh perl-DBD-MySQL-3.0007-2.el5.x86_64.rpm

warning: perl-DBD-MySQL-3.0007-2.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186

Preparing... ########################################### [100%]

1:perl-DBD-MySQL ########################################### [100%]

[root@/]#



[root@ /]# rpm -ivh mysql-server-5.0.77-4.el5_6.6.x86_64.rpm
warning: mysql-server-5.0.77-4.el5_6.6.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing... ########################################### [100%]
1:mysql-server ########################################### [100%]
[root@ /



OR



$yum install mysql-server mysql

* Verify istalled packages :

$rpm -qa |egrep -i 'mysql|perl-DBD-MySQL|perl-DBI|mysql-server'

perl-DBD-MySQL-3.0007-2.el5

perl-DBI-1.52-2.el5

mysql-server-5.0.77-4.el5_6.6

mysql-5.0.77-4.el5_6.6

mysql-5.0.77-4.el5_6.6

* Start mysqld service :

$/etc/init.d/mysqld restart
Stopping MySQL: [FAILED]
Initializing MySQL database: Installing MySQL system tables...
OK
Filling help tables...
OK



To start mysqld at boot time you have to copy
support-files/mysql.server to the right place for your system



PLEASE REMEMBER TO SET A PASSWORD FOR THE MySQL root USER !
To do so, start the server, then issue the following commands:
/usr/bin/mysqladmin -u root password 'new-password'
/usr/bin/mysqladmin -u root -h dhcp209-14.gsslab.pnq.redhat.com password 'new-password'



Alternatively you can run:
/usr/bin/mysql_secure_installation



which will also give you the option of removing the test
databases and anonymous user created by default. This is
strongly recommended for production servers.



See the manual for more instructions.



You can start the MySQL daemon with:
cd /usr ; /usr/bin/mysqld_safe &



You can test the MySQL daemon with mysql-test-run.pl
cd mysql-test ; perl mysql-test-run.pl



Please report any problems with the /usr/bin/mysqlbug script!



The latest information about MySQL is available on the web at
http://www.mysql.com
Support MySQL by buying support/licenses at http://shop.mysql.com
[ OK ]
Starting MySQL: [ OK ]
[root@]# /etc/init.d/mysqld status
mysqld (pid 15065) is running...



[root@]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.0.77 Source distribution



Type 'help;' or '\h' for help. Type '\c' to clear the buffer.



mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| test |
+--------------------+
3 rows in set (0.00 sec)



mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A



Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql |
+---------------------------+
| columns_priv |
| db |
| func |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| host |
| proc |
| procs_priv |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user |
+---------------------------+
17 rows in set (0.00 sec)



mysql> quit
Bye
[root@dhcp209-14 /]# netstat -plan |grep :3306
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 15065/mysqld
[root@dhcp209-14 /]#
----------

mysql> show variables like '%%ssl%%';
+---------------+----------+
| Variable_name | Value |
+---------------+----------+
| have_openssl | DISABLED |
| have_ssl | DISABLED |
| ssl_ca | |
| ssl_capath | |
| ssl_cert | |
| ssl_cipher | |
| ssl_key | |
+---------------+----------+
7 rows in set (0.00 sec)

mysql>

* Reset mysql root password :

$/usr/bin/mysqladmin -u root password 'mysql'

* Configurring SSL for mysql server and client(who will access server) :

$mkdir -p /etc/mysql/newcerts

$chown -R mysql:mysql /etc/mysql/newcerts

* Creating certificate autority :

$cd /etc/mysql/newcerts

$openssl genrsa 2048 > ca-key.pem
$openssl req -new -x509 -nodes -days 1000 -key ca-key.pem > ca-cert.pem

* Creating certificate for server using above CA certificate :

$openssl req -newkey rsa:2048 -days 1000 -nodes -keyout server-key.pem > server-req.pem
$openssl x509 -req -in server-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 > server-cert.pem

* Creating cerificate for client using above CA certificate(similar like server) :

$openssl req -newkey rsa:2048 -days 1000 -nodes -keyout client-key.pem > client-req.pem
$openssl x509 -req -in client-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 > client-cert.pem

* Make sure following entries are present in /etc/my.cnf file :

[mysqld]

datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).
old_passwords=1



# Disabling symbolic-links is recommended to prevent assorted security risks;
# to do so, uncomment this line:
# symbolic-links=0
ssl # < ssl-ca=/etc/mysql/newcerts/ca-cert.pem # << Important.
ssl-cert=/etc/mysql/newcerts/server-cert.pem # << Important
ssl-key=/etc/mysql/newcerts/server-key.pem # << Important



[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

* Execute following commands (Used "mysql" password for user "mysql"):

$/etc/init.d/mysqld restart

$mysql -u root -p

$mysql> GRANT ALL ON *.* TO 'mysql'@'%' IDENTIFIED BY 'mysql' REQUIRE SSL;

* Testing :

$cd /etc/mysql/newcerts

$mysql --ssl-cert=ca-cert.pem --ssl-key=client-key.pem --ssl-cert=client-cert.pem -u root -p -v -v -v

Enter password: << pw = mysql

Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.0.77 Source distribution



Reading history-file /root/.mysql_history
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.



mysql> SHOW STATUS LIKE 'Ssl_cipher';
--------------
SHOW STATUS LIKE 'Ssl_cipher'
--------------



+---------------+--------------------+
| Variable_name | Value |
+---------------+--------------------+
| Ssl_cipher | DHE-RSA-AES256-SHA | < +---------------+--------------------+
1 row in set (0.00 sec)



mysql> show variables like '%%ssl%%';
--------------
show variables like '%%ssl%%'
--------------



+---------------+-------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------+
| have_openssl | YES | < | have_ssl | YES | < | ssl_ca | /etc/mysql/newcerts/ca-cert.pem |
| ssl_capath | |
| ssl_cert | /etc/mysql/newcerts/server-cert.pem |
| ssl_cipher | |
| ssl_key | /etc/mysql/newcerts/server-key.pem |
+---------------+-------------------------------------+
7 rows in set (0.01 sec)



mysql> quit
Writing history-file /root/.mysql_history
Bye





[root@]# mysql --ssl-cert=/etc/mysql/newcerts/ca-cert.pem --ssl-key=/etc/mysql/newcerts/client-key.pem --ssl-cert=/etc/mysql/newcerts/client-cert.pem -u root -p -v -v -v
Enter password: << pw = mysql



Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.0.77 Source distribution



Reading history-file /root/.mysql_history
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.



mysql> show variables like '%%ssl%%';
--------------
show variables like '%%ssl%%'
--------------



+---------------+-------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------+
| have_openssl | YES |
| have_ssl | YES |
| ssl_ca | /etc/mysql/newcerts/ca-cert.pem |
| ssl_capath | |
| ssl_cert | /etc/mysql/newcerts/server-cert.pem |
| ssl_cipher | |
| ssl_key | /etc/mysql/newcerts/server-key.pem |
+---------------+-------------------------------------+
7 rows in set (0.01 sec)



mysql> SHOW STATUS LIKE 'Ssl_cipher';
--------------
SHOW STATUS LIKE 'Ssl_cipher'
--------------



+---------------+--------------------+
| Variable_name | Value |
+---------------+--------------------+
| Ssl_cipher | DHE-RSA-AES256-SHA | << Confirmed
+---------------+--------------------+
1 row in set (0.00 sec)


mysql>

mysql> quit

Read More

How to generate UDP packets and capture them?

Guys,

I had a chance to generate UDP packets and send them to another host. This was needed for testing a specific problem that I had faced. The problem is that I had to see huge Recv-Q at "netstat -apln|grep -i 'syslog' prior to RHEL 5.4. Now question is why does it show such huge value? But why do we see this at first place? No, we didn't see it at first place. Actually one monitoring software was complaining that there were lot of failure d UDP packets in "netstat -s" output and it also complained that number of such packets were also huge in Recv-Q. So, I had to investigate in detail.

As you know Recv-Q = Number of bytes received from network as well as from local machine and that will be processed by syslog, so syslogd was not processing received UDP pkts.

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
udp 653212 0 0.0.0.0:514 0.0.0.0:* LISTEN syslog

As per my knowledge 0 0.0.0.0 = any.any.any.any address. And syslog collects messages from /dev/log. Also klogd sends kernel error/warning messages to syslogd. Syslogd filters the messages as per rules defined in /etc/syslog.conf and redirects them to corresponding log file. Big question is that if rule doesn't match then do the messages will be really going to log files(say /var/log/messages)? I think they will go if we accepts network messages. Pass "-r" to syslogd ie /etc/sysconfig/syslog.

---------> | /dev/log, klogd ----->| ------->syslogd ------>filter------->system log, @remote_server
---------> | ----->|

My concept about receiving the packets :

NIC -->NIC_DRIVER---->hrd_IRQ---->soft_IRQ---->PRE_ROUTING---->packet_forwarding---->libpcap(tcpdump)---->hook(INPUT)--->SKB--->CPU

I tried to send UDP packets locally and captured UDP by tcpdump. I have used server.c and rawudp.c two programs. So, server.c should be running to listen udp packets whereas rawudp.c will send udp packets. I took help from a guy to get these programs. I was trying to do using perl but there were lot of dependencies. So, I avoided it to use it. My intenstion was to verify whether Recv-Q was increasing by hitting UDP packets to server. But this does't increase. Note that I sent raw UDP packets. tcpdump data gave clear picture about source, destination, source and destination ports.

Here are the exact source codes and testing procedures :

------server.c---------
#include
#include
#include
#include
#include
#include

#define BUFLEN 512
#define NPACK 10
#define PORT 9930

void diep(char *s)
{
perror(s);
exit(1);
}

int main(void)
{
struct sockaddr_in si_me, si_other;
int s, i, slen=sizeof(si_other);
char buf[BUFLEN];

if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
diep("socket");

memset((char *) &si_me, 0, sizeof(si_me));
si_me.sin_family = AF_INET;
si_me.sin_port = htons(PORT);
si_me.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(s, &si_me, sizeof(si_me))==-1)
diep("bind");

for (i=0; i if (recvfrom(s, buf, BUFLEN, 0, &si_other, &slen)==-1)
diep("recvfrom()");
printf("Received packet from %s:%d\nData: %s\n\n",
inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port), buf);
}

close(s);
return 0;
}
------server.c--------


------rawudp.c-------
/*
Copyright 2010 Gabriel Serme

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include

#define LEN 512

typedef unsigned short u16;
typedef unsigned long u32;

//2nd
unsigned short csum (unsigned short *buf, int nwords);
uint16_t udp_checksum(const struct iphdr *ip,
const struct udphdr *udp,
const uint16_t *buf);



int main(int argc, char * argv[])
{

# if __BYTE_ORDER == __LITTLE_ENDIAN //reverse per 8 bits
printf("little endian\n");
#else
printf("big endian\n");
#endif

if(argc != 5)
{
printf("- Usage %s \n", argv[0]);
exit(1);
}else{
printf ("Args : \n"
"\tip source : %s:%s\n"
"\tip dest : %s:%s\n",
argv[1], argv[2], argv[3], argv[4]);
}
int PSOURCE = atoi (argv[2]);
int PDEST = atoi(argv[4]);
char * SOURCE = argv[1];
char * DEST = argv[3];
char * ANSWER = argv[5];
int s;
struct sockaddr_in daddr, saddr, answerip;
char packet[LEN];
/* point the iphdr to the beginning of the packet */
struct iphdr *ip = (struct iphdr *)packet;
struct udphdr *udp = (struct udphdr *)((void *) ip + sizeof(struct iphdr));
struct dnshdr *dns = (struct dnshdr *)((void *) udp + sizeof(struct udphdr));

if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}

daddr.sin_family = AF_INET;
saddr.sin_family = AF_INET;
daddr.sin_port = htons(PDEST);
saddr.sin_port = htons(PSOURCE);
inet_pton(AF_INET, DEST, (struct in_addr *)&daddr.sin_addr.s_addr);
inet_pton(AF_INET, SOURCE, (struct in_addr *)&saddr.sin_addr.s_addr);

memset(daddr.sin_zero, 0, sizeof(daddr.sin_zero));
memset(saddr.sin_zero, 0, sizeof(saddr.sin_zero));
memset(udp, 0, sizeof(struct udphdr));
memset(ip, 0, sizeof(struct iphdr));

ip->ihl = 5; //header length
ip->version = 4;
ip->tos = 0x0;
ip->id = 0;
ip->frag_off = htons(0x4000); /* DF */
ip->ttl = 64; /* default value */
ip->protocol = 17; //IPPROTO_RAW; /* protocol at L4 */
ip->check = 0; /* not needed in iphdr */
ip->saddr = saddr.sin_addr.s_addr;
ip->daddr = daddr.sin_addr.s_addr;

udp->source = htons(PSOURCE);
udp->dest = htons (PDEST);

int sizedata = 100;
memset(((void *) udp) + sizeof(struct udphdr), 'A', sizedata);

int sizeudpdata = sizeof(struct udphdr) + sizedata;
ip->tot_len = htons(sizeudpdata + sizeof(struct iphdr)); /* 16 byte value */
udp->len = htons(sizeudpdata);

udp->check = udp_checksum(
ip,
udp,
udp);
printf ("Checksum : 0x%x\n", udp->check);
printf ("Sizes : \n\t[+] iphdr %d"
"\n\t[+] udphdr %d\n",
sizeof(struct iphdr), sizeof(struct udphdr));
printf ("Total size : %d\n", sizeudpdata);

int optval = 1;

if (setsockopt(s, IPPROTO_IP, IP_HDRINCL, &optval, sizeof(int))
< 0)
perror ("IP HDRINCL");

while(1) {
int sizepacket = sizeof(struct iphdr) + sizeudpdata;
if (sendto(s, (char *)packet, sizepacket, 0,
(struct sockaddr *)&daddr, (socklen_t)sizeof(daddr)) < 0)
perror("packet send error:");
else
printf("Sent packet\n");
sleep(2);
}
exit(EXIT_SUCCESS);
}

//http://www.linuxquestions.org/questions/linux-networking-3/udp-checksum-algorithm-845618/
//modified by Gabriel Serme
struct pseudo_hdr {
u_int32_t source;
u_int32_t dest;
u_int8_t zero; //reserved, check http://www.rhyshaden.com/udp.htm
u_int8_t protocol;
u_int16_t udp_length;
};

uint16_t udp_checksum(const struct iphdr *ip,
const struct udphdr *udp,
const uint16_t *buf)
{
//take in account padding if necessary
int calculated_length = ntohs(udp->len)%2 == 0 ? ntohs(udp->len) : ntohs(udp->len) + 1;

struct pseudo_hdr ps_hdr = {0};
bzero (&ps_hdr, sizeof(struct pseudo_hdr));
uint8_t data[sizeof(struct pseudo_hdr) + calculated_length];
bzero (data, sizeof(struct pseudo_hdr) + calculated_length );

ps_hdr.source = ip->saddr;
ps_hdr.dest = ip->daddr;
ps_hdr.protocol = IPPROTO_UDP; //17
ps_hdr.udp_length = udp->len;

memcpy(data, &ps_hdr, sizeof(struct pseudo_hdr));
memcpy(data + sizeof(struct pseudo_hdr), buf, ntohs(udp->len) ); //the remaining bytes are set to 0

return csum((uint16_t *)data, sizeof(data)/2);
}

/* Not my code */
unsigned short csum (unsigned short *buf, int nwords)
{
unsigned long sum;

for (sum = 0; nwords > 0; nwords--)
sum += *buf++;

sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
return ~sum;
}
--------rawudp.c--------

Compile programs :

$gcc -o server server.c
$gcc -o rawudp rawudp.c

You'll see server and rawudp files.

--------------------------------

Testing :

./server //server is ready to listen UDP which will be sent from rawudp prgram.
$tcpdump -i lo -X -vv 'port 9930' -w captured.pcap //I am sniffing it on another terminal.(Note that server port is 9930)

./rawudp 127.0.0.1 1111 127.0.0.1 9930 //sending raw packets to localhost on another terminal(destination is 127.0.0.1 and its port is 9930. source port is 1111 )
src src_port dst_h dst_p


$wireshark captured.pcap //Viewing captured UDP packets

------------------------------

Conclusion :

a) Firewall was enabled : $iptables -A INPUT -s 127.0.0.1 -p udp -j DROP ,
So, ./sever did't listen any udp packets. //Test was done

Ou put :

./server
Received packet from 127.0.0.1:1112
Data: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA //16bytes

Received packet from 127.0.0.1:1112
Data: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Received packet from 127.0.0.1:1112
Data: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Received packet from 127.0.0.1:1112
Data: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

These messages will be stopped once I again execute "iptables -A INPUT -s 127.0.0.1 -p udp -j DROP". But I saw that number of packets capturing in tcpdump was increasing. And rawudp was continuosly sending udp packets.

Result :

[root@vm ~]# tcpdump -i lo -X -vv 'port 9930' -w gaby.dump3_blokupd
tcpdump: listening on lo, link-type EN10MB (Ethernet), capture size 96 bytes
Got 37


[root@vm122 myUDP]# ./rawudp 127.0.0.1 1112 127.0.0.1 9930
little endian
Args :
ip source : 127.0.0.1:1112
ip dest : 127.0.0.1:9930
Checksum : 0x3317
Sizes :
[+] iphdr 20
[+] udphdr 8
Total size : 108
Sent packet


Sent packet
Sent packet
Sent packet
. . . .
---------------------

Why Recv-Q is so high :

1. DNS server was sending lot of UDP(LLMNR) packets.
2. Local machine was sending lot of UDP(LLC) packets.
3. Some machines which are in same subnet were sending UDP to other machines(Don't know why libpcap captured them. Did they route after passing through tcpdump? I still have doubt)
4. Increase size of rmem kernel memory.

Read More

How to configure rndc key with chrooted bind on linux?

Environment : RHEL 6.1 .

Here are the steps that I followed :

1. vi /etc/rndc.conf and following line

----
options {
default-server 127.0.0.1;
default-key "rndckey";
};

server 127.0.0.1 {
key "rndckey";
};

key "rndckey" {
algorithm "hmac-md5";
secret "secret key will be placed here";
};
---

2. cd /var/named/chroot/etc/

3. $dnssec-keygen -r /dev/urandom -a HMAC-MD5 -b 256 -n HOST rndc
4. cat *.private
5. copy the key from private file and put it in /etc/rndc.conf at "secret" line.
6. Do link :

$ln -s /var/named/chroot/etc/rndc.conf /etc/rndc.conf

7. vi /etc/named.conf put following :

----
controls {
inet 127.0.0.1 allow { 127.0.0.1; } keys { rndckey; };
};

key "rndckey" {
algorithm "hmac-md5";
secret "replace_keyhere";
};

----

8. Restart named and check status :

$rndc status

Output will look like :

$rndc status
version: 9.7.3-P3-RedHat-9.7.3-2.el6_1.P3.2
CPUs found: 1
worker threads: 1
number of zones: 20
debug level: 0
xfers running: 0
xfers deferred: 0
soa queries in progress: 0
query logging is OFF
recursive clients: 0/0/1000
tcp clients: 0/100
server is up and running

Read More

How to rotate sudo log?

Scenario : Sudo log files will keep the activities of sudo users and their login status in /var/log/sudolog.

Tested platform : RHEL 5

Solution :

1. Create a sudo log file and put it in /etc/sudoers. Then rotate it for 90 days. As an example :

$touch /var/log/sudolog

2. vi /etc/sudoers and add following lines :

-----
Defaults !syslog
Defaults logfile = /var/log/sudolog
-----

Then save it.

3. Rotating this log file :

vi /etc/logrotate.d/sudolog and put following :

------
/var/log/sudolog {
rotate 90
size 5M
postrotate
/usr/bin/killall -HUP syslogd
endscript
}
------

4. Now restart syslogd :

$service syslogd restart

This will keep maximum 5MB file of 90 different copies. Old copy will be removed first.

Read More