RHEL-6 (4)
KNOW
YOUR SYSTEM-P4
NETWORK:
Under "KNOW YOUR SYSTEM"
What is IP/Subnet & gateway of my
system?
What is MAC address of my particular
Ethernet port?
How to know about the existing routes in
system?
How can i make a interface up and down?
How to ping with particular no of counts?
How to trace the route/path of a particular
IP?
What are the meanings of different O/P's
from traceroute?
How to dump the TCP packets?
What is ARP?
How to add Static ARP Entry on my system?
How to add Static ARP Entries Permanently on
my system?
How to delete a Static ARP Entry from my
system?
How to print systems routing table?
How to add the route for Host / Network?
How to remove the route?
What are the important files and their
descriptions in my system?
IP/Subnet/Gateway/Routes/Interface
[root@rhel6-client1 /]# ifconfig –a
[root@rhel6-client1 /]# ifconfig eth3
eth3 Link
encap:Ethernet HWaddr 00:0C:29:80:4E:54
inet addr:192.168.110.135 Bcast:192.168.110.255 Mask:255.255.255.0
inet6 addr:
fe80::20c:29ff:fe80:4e54/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500
Metric:1
RX packets:10648
errors:0 dropped:0 overruns:0 frame:0
TX packets:7062
errors:0 dropped:0 overruns:0 carrier:0
collisions:0
txqueuelen:1000
RX bytes:795216
(776.5 KiB) TX bytes:4482794 (4.2 MiB)
[root@rhel6-client1 /]# cat
/etc/sysconfig/network-scripts/ifcfg-eth3
DEVICE=eth3
TYPE=Ethernet
UUID=aff36e84-11b8-4d37-8243-79ba0798839f
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=none
HWADDR=00:0C:29:80:4E:54 çMAC address of eth3
IPADDR=192.168.110.135 çIP of eth3
PREFIX=24 ç Subnet
GATEWAY=192.168.234.2 ç Gateway
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth3"
BOOTPROTO=<protocol>
where <protocol> is one of the following:
none — No boot-time protocol should be used.
bootp — The BOOTP protocol should be used.
dhcp — The DHCP protocol should be used.
BROADCAST=<address>
where <address> is the broadcast address. This directive is
deprecated, as the value is calculated automatically with ifcalc.
DEVICE=<name>
where <name> is the name of the physical device (except for
dynamically-allocated PPP devices where it is the logical name).
DHCP_HOSTNAME
Use this option only if the DHCP server requires the client to
specify a hostname before receiving an IP address.
DNS{1,2}=<address>
where <address> is a name server address to be placed in
/etc/resolv.conf if the PEERDNS directive is set to yes.
ETHTOOL_OPTS=<options>
where <options> are any device-specific options supported by
ethtool. For example, if you wanted to force 100Mb, full duplex:
ETHTOOL_OPTS="autoneg off speed 100 duplex full"
Instead of a custom initscript, use ETHTOOL_OPTS to set the interface
speed and duplex settings. Custom initscripts run outside of the network init
script lead to unpredictable results during a post-boot network service
restart.
GATEWAY=<address>
where <address> is the IP address of the network router or
gateway device (if any).
HWADDR=<MAC-address>
where <MAC-address> is the hardware address of the Ethernet
device in the form AA:BB:CC:DD:EE:FF. This directive is useful for machines
with multiple NICs to ensure that the interfaces are assigned the correct
device names regardless of the configured load order for each NIC's module.
This directive should not be used in conjunction with MACADDR.
IPADDR=<address>
where <address> is the IP address.
MACADDR=<MAC-address>
where <MAC-address> is the hardware address of the Ethernet
device in the form AA:BB:CC:DD:EE:FF. This directive is used to assign a MAC
address to an interface, overriding the one assigned to the physical NIC. This
directive should not be used in conjunction with HWADDR.
MASTER=<bond-interface>
where <bond-interface> is the channel bonding interface to
which the Ethernet interface is linked.
This directive is used in conjunction with the SLAVE directive.
Refer to Section 14.2.3, “Channel Bonding Interfaces” for more
information about channel bonding interfaces.
NETMASK=<mask>
where <mask> is the netmask value.
NETWORK=<address>
where <address> is the network address. This directive is
deprecated, as the value is calculated automatically with ifcalc.
ONBOOT=<answer>
where <answer> is one of the following:
yes — This device should be activated at boot-time.
no — This device should not be activated at boot-time.
PEERDNS=<answer>
where <answer> is one of the following:
yes — Modify /etc/resolv.conf if the DNS directive is set. If using
DHCP, then yes is the default.
no — Do not modify /etc/resolv.conf.
SLAVE=<bond-interface>
where <bond-interface> is one of the following:
yes — This device is controlled by the channel bonding interface
specified in the MASTER directive.
no — This device is not controlled by the channel bonding interface
specified in the MASTER directive.
This directive is used in conjunction with the MASTER directive.
Refer to Section 14.2.3, “Channel Bonding Interfaces” for more about
channel bonding interfaces.
SRCADDR=<address>
where <address> is the specified source IP address for outgoing
packets.
USERCTL=<answer>
where <answer> is one of the following:
yes — Non-root users are allowed to control this device.
no — Non-root users are not allowed to control
this device.
To list all the existing routes in system or server.
[root@rhel6-server ~]# route
Kernel
IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.110.0 192.168.110.1 255.255.255.0 UG
0 0 0 eth3
192.168.110.0 * 255.255.255.0 U
0 0 0 eth3
192.168.234.0 *
255.255.255.0 U
0 0 0 eth2
192.168.234.0 * 255.255.255.0 U
1 0 0 eth1
link-local * 255.255.0.0 U
1004 0 0 eth2
link-local * 255.255.0.0 U
1005 0 0 eth3
default 192.168.234.2 0.0.0.0 UG
0 0 0 eth1
[root@rhel6-server ~]# route -n
Kernel
IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.110.0 192.168.110.1 255.255.255.0 UG
0 0 0 eth3
192.168.110.0 0.0.0.0 255.255.255.0 U
0 0 0 eth3
192.168.234.0 0.0.0.0 255.255.255.0 U
0 0 0 eth2
192.168.234.0 0.0.0.0 255.255.255.0 U
1 0 0 eth1
169.254.0.0 0.0.0.0 255.255.0.0 U
1004 0 0 eth2
169.254.0.0 0.0.0.0 255.255.0.0 U
1005 0 0 eth3
0.0.0.0 192.168.234.2 0.0.0.0 UG
0 0 0
eth1
INTERFACE UP-DOWN:
[root@rhel6-server ~]# ifconfig eth1 down
[root@rhel6-server ~]# ifconfig eth1 up
OR
[root@rhel6-server ~]# ifdown eth1
Device state: 3 (disconnected)
[root@rhel6-server ~]# ifconfig eth1
eth1 Link
encap:Ethernet HWaddr 00:0C:29:80:4E:40
inet6 addr:
fe80::20c:29ff:fe80:4e40/64 Scope:Link
UP BROADCAST RUNNING
MULTICAST MTU:1500 Metric:1
RX packets:3125
errors:0 dropped:0 overruns:0 frame:0
TX packets:43
errors:0 dropped:0 overruns:0 carrier:0
collisions:0
txqueuelen:1000
RX bytes:290548
(283.7 KiB) TX bytes:4754 (4.6 KiB)
[root@rhel6-server ~]# ifup eth1
Active connection state: activated
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/7
[root@rhel6-server ~]# ifconfig eth1
eth1 Link
encap:Ethernet HWaddr 00:0C:29:80:4E:40
inet
addr:192.168.234.146
Bcast:192.168.234.255
Mask:255.255.255.0
inet6 addr:
fe80::20c:29ff:fe80:4e40/64 Scope:Link
UP BROADCAST RUNNING
MULTICAST MTU:1500 Metric:1
RX packets:3125
errors:0 dropped:0 overruns:0 frame:0
TX packets:43
errors:0 dropped:0 overruns:0 carrier:0
collisions:0
txqueuelen:1000
RX bytes:290548
(283.7 KiB) TX bytes:4754 (4.6 KiB)
[root@rhel6-server ~]# ifcfg
Usage: ifcfg DEV [[add|del [ADDR[/LEN]] [PEER] | stop]
add - add new address
del - delete address
stop - completely
disable IP
CONNECTIVITY:
[root@rhel6-server ~]# ping 192.168.234.144
PING
192.168.234.144 (192.168.234.144) 56(84) bytes of data.
64
bytes from 192.168.234.144: icmp_seq=1 ttl=64 time=3.79 ms
64
bytes from 192.168.234.144: icmp_seq=2 ttl=64 time=0.666 ms
64
bytes from 192.168.234.144: icmp_seq=3 ttl=64 time=0.559 ms
^C
---
192.168.234.144 ping statistics ---
3
packets transmitted, 3 received, 0% packet loss, time 2148ms
rtt
min/avg/max/mdev = 0.559/1.671/3.790/1.499 ms
[root@rhel6-server ~]# ping -c 5 192.168.234.144
PING 192.168.234.144 (192.168.234.144) 56(84) bytes of data.
64
bytes from 192.168.234.144: icmp_seq=1 ttl=64 time=0.917 ms
64
bytes from 192.168.234.144: icmp_seq=2 ttl=64 time=0.826 ms
64
bytes from 192.168.234.144: icmp_seq=3 ttl=64 time=0.664 ms
64
bytes from 192.168.234.144: icmp_seq=4 ttl=64 time=0.789 ms
64
bytes from 192.168.234.144: icmp_seq=5 ttl=64 time=0.576 ms
---
192.168.234.144 ping statistics ---
5
packets transmitted, 5 received, 0% packet loss, time 4006ms
rtt
min/avg/max/mdev = 0.576/0.754/0.917/0.123 ms
[root@rhel6-server ~]# traceroute 192.168.234.200
traceroute to 192.168.234.200 (192.168.234.200), 30 hops max, 60 byte
packets
1 192.168.234.200
(192.168.234.200) 4.181 ms 2.774 ms
3.017 ms
[root@rhel6-server ~]# tracepath 192.168.234.200
1: rhel6-server (192.168.234.146) 0.384ms pmtu 1500
1: 192.168.234.200 (192.168.234.200) 0.901ms reached
1: 192.168.234.200 (192.168.234.200) 0.963ms reached
Resume: pmtu 1500 hops 1
back 64
Traceroute Symbol
|
Description
|
***
|
Expected 5 second response time exceeded.
Could be caused by:
* A router on the path not sending back the ICMP "time exceeded" messages * A router or firewall in the path blocking the ICMP "time exceeded" messages * The target IP address not responding |
!H, !N, or !P
|
Host, network or protocol
unreachable
|
!X or !A
|
Communication administratively prohibited. A router Access Control List
(ACL) or firewall is in the way
|
!S
|
Source route failed. Source routing
attempts to force traceroute touse a certain path. Failure might be due to a
router security setting
|
[root@rhel6-server ~]# tcpdump -i eth1
tcpdump: verbose output suppressed, use -v or -vv for full protocol
decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535
bytes
04:43:28.670872 IP 192.168.234.1.64548 > 239.255.255.250.ssdp:
UDP, length 94
04:43:28.886322 IP 192.168.234.1.64553 > 239.255.255.250.ssdp:
UDP, length 119
^C
2 packets captured
2 packets received by filter
0 packets dropped by kernel
[root@rhel6-server ~]# tcpdump -i eth3
tcpdump: verbose output suppressed, use -v or -vv for full protocol
decode
listening on eth3, link-type EN10MB (Ethernet), capture size 65535
bytes
04:43:59.006647 IP rhel6-server.ssh > 192.168.110.1.raven-rmp:
Flags [P.], seq 2289578414:2289578610, ack 225829094, win 146, length 196
04:43:59.007204 IP 192.168.110.1.raven-rmp > rhel6-server.ssh:
Flags [.], ack 196, win 16324, length 0
04:43:59.009094 IP rhel6-server.ssh > 192.168.110.1.raven-rmp:
Flags [P.], seq 196:488, ack 1, win 146, length 292
04:43:59.009481 IP 192.168.110.1.raven-rmp > rhel6-server.ssh:
Flags [.], ack 488, win 16251, length 0
=================O/P REMOVED======================================
^C
3674 packets captured
3676 packets received by filter
0 packets dropped by kernel
ARP:
Arp is used to translate IP addresses into Ethernet addresses. The
arp table is stored in the kernel and manipulated dynamically. Arp entries are
cached and will time out and are deleted normally in 20 minutes.
arp –a : Prints the arp table
arp –s <ip_address> <mac_address> [pub] to add an entry
in the table
arp –a –d to delete all the entries in the ARP table
[root@rhel6-server ~]# arp -a
? (192.168.110.1) at 00:50:56:c0:00:01 [ether] on eth3
Add an static entry
[root@rhel6-server ~]# arp -s 192.168.234.2
00:0C:29:80:4E:40
Check the status,
[root@rhel6-server ~]# arp -a -n
? (192.168.110.1) at 00:0C:29:80:4E:54 [ether] on eth3
? (192.168.234.2) at 00:0c:29:80:4e:40 [ether] PERM on eth2
Make it permanent,
[root@rhel6-server ~]# vi /etc/ethers
# see man ethers for syntax
00:0C:29:80:4E:40 192.168.234.146
00:0C:29:80:4E:54 192.168.110.135
Delete an static entry,
[root@rhel6-server ~]# arp -d 192.168.110.1
ROUTE:
Print routing table.
[root@rhel6-server ~]# netstat -nr
Kernel
IP routing table
Destination Gateway Genmask Flags
MSS Window irtt Iface
192.168.110.0 0.0.0.0 255.255.255.0 U
0 0 0 eth3
192.168.234.0 192.168.234.2 255.255.255.0 UG
0 0 0 eth1
192.168.234.0 0.0.0.0 255.255.255.0 U
0 0 0 eth2
192.168.234.0 0.0.0.0 255.255.255.0 U
0 0 0 eth1
0.0.0.0 192.168.234.2 0.0.0.0 UG 0 0 0 eth1
[root@rhel6-server ~]# netstat –rnf inet
Active
Internet connections (w/o servers)
Proto
Recv-Q Send-Q Local Address
Foreign Address State
tcp 0
0 rhel6-server:ssh
192.168.110.1:bintec-tapi
ESTABLISHED
tcp 0
0 rhel6-server:ssh
192.168.110.1:simp-all
ESTABLISHED
Active
UNIX domain sockets (w/o servers)
Proto
RefCnt Flags Type State I-Node Path
unix 23
[ ] DGRAM 12608 /dev/log
unix 2
[ ] DGRAM 8728 @/org/kernel/udev/udevd
unix 2
[ ] DGRAM 14214 @/org/freedesktop/hal/udev_event
unix 2
[ ] DGRAM 51238
unix 2
[ ] DGRAM 49750
unix 2
[ ] DGRAM 34933
unix 3
[ ] STREAM CONNECTED 25255
@/tmp/dbus-ThzIS4OuAz
=================O/P REMOVED======================================
[root@rhel6-server ~]# netstat –an
With the -an option lists all the TCP ports on which Linux server is
listening including all the active network connections to and from server. This
can be very helpful in determining whether slowness is due to high traffic
volumes:
#route add|delete [-net|-host] <destination>
<gateway>
[root@rhel6-server ~]# route add -net 192.168.234.0/24 gw
192.168.234.2 eth1
#route flush - it removes all the routes
#route add -net 0.0.0.0 192.168.234.2 - to add a default
route
[root@rhel6-server ~]# route del -net 192.168.234.0/24 gw
192.168.234.2 eth1
IMPORTANT FILES:
/etc/hosts —- names to ip addresses
/etc/networks —- network names to ip addresses
/etc/protocols —– protocol names to protocol numbers
/etc/services —- tcp/udp service names to port numbers
/etc/hosts
The main purpose of this file is to resolve host names that cannot be
resolved any other way. It can also be used to resolve host names on small
networks with no DNS server. Regardless of the type of network the computer is
on, this file should contain a line specifying the IP address of the loopback
device (127.0.0.1) as localhost.localdomain.
/etc/resolv.conf
This file specifies the IP addresses of DNS servers and the search
domain. Unless configured to do otherwise, the network initialization scripts populate
this file.
/etc/sysconfig/network
This file specifies routing and host information for all network
interfaces. It is used to contain directives which are to have global effect
and not to be interface specific.
/etc/sysconfig/network-scripts/ifcfg-interface-name
For each network interface, there is a corresponding interface
configuration script. Each of these files provide information specific to a
particular network interface.
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