[CentOS] Routing of outgoing packets

Mitja Mihelič mitja.mihelic at arnes.si
Fri Oct 1 04:30:35 EDT 2010


On 09/30/2010 05:02 PM, John Doe wrote:
> From: Mitja Mihelič<mitja.mihelic at arnes.si>
>> I am trying to use hping to chek the latency of our network.
>> Somehow things are not going to plan and I thought someone might be able
>> to shed some light on the subject.
>> Here is the setup:
>> (the IP addresses gvien here are fake, but they do represent the correct
>> state of the networking setup)
>> vlan      interface      IP                      mask
>> V2        eth0           192.168.20.20    32
>> V4        eth1           172.16.4.40        32
>> V6        eth2           172.16.6.60        32
>>
>> The default route is set to eth1.
>> The idea is to use eth2 for pinging only, the other two interfaces are
>> used by another service and management access.
> Could you show the ifconfig and route outputs...?
>
> JD
The Centos version is 5.5.

This is the kernel we are using 
(http://rpms.mcnc.org/web100/el5/distro-compat/i386/):
2.6.18-164.15.1.el5.web100PAE #1 SMP Mon May 17 17:01:51 EDT 2010 i686 
athlon i386 GNU/Linux

The IP addresses are presented as private addresses, netmasks are real.

Here is the ifconfig output:
[root at server ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:16:35:82:45:A0
           inet addr:192.168.254.236  Bcast:192.168.254.239  
Mask:255.255.255.240
           inet6 addr: fe80::216:35ff:fe82:45a0/64 Scope:Link
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:139602 errors:0 dropped:0 overruns:0 frame:0
           TX packets:58914 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:211203420 (201.4 MiB)  TX bytes:4285647 (4.0 MiB)
           Interrupt:186 Memory:dc000000-dc012800

eth1      Link encap:Ethernet  HWaddr 00:16:35:82:45:A2
           inet addr:192.168.254.244  Bcast:192.168.254.247  
Mask:255.255.255.248
           inet6 addr: fe80::216:35ff:fe82:45a2/64 Scope:Link
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:15 errors:0 dropped:0 overruns:0 frame:0
           TX packets:14 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:1130 (1.1 KiB)  TX bytes:1116 (1.0 KiB)
           Interrupt:194 Memory:da000000-da012800

eth2      Link encap:Ethernet  HWaddr 00:15:17:C5:84:4D
           inet addr:192.168.254.18  Bcast:192.168.254.23  
Mask:255.255.255.248
           inet6 addr: fe80::215:17ff:fec5:844d/64 Scope:Link
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:29 errors:0 dropped:0 overruns:0 frame:0
           TX packets:18 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:2280 (2.2 KiB)  TX bytes:1236 (1.2 KiB)
           Memory:dfde0000-dfe00000

lo        Link encap:Local Loopback
           inet addr:127.0.0.1  Mask:255.0.0.0
           inet6 addr: ::1/128 Scope:Host
           UP LOOPBACK RUNNING  MTU:16436  Metric:1
           RX packets:21 errors:0 dropped:0 overruns:0 frame:0
           TX packets:21 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:4240 (4.1 KiB)  TX bytes:4240 (4.1 KiB)


And the route command output:
[root at server ~]# route -n
Kernel IP routing table
Destination      Gateway          Genmask          Flags Metric Ref    
Use Iface
192.168.18.122   192.168.254.225  255.255.255.255  UGH   0      0        
0 eth0
192.168.254.16   0.0.0.0          255.255.255.248  U     0      0        
0 eth2
192.168.254.240  0.0.0.0          255.255.255.248  U     0      0        
0 eth1
192.168.18.160   192.168.254.225  255.255.255.240  UG    0      0        
0 eth0
192.168.254.224  0.0.0.0          255.255.255.240  U     0      0        
0 eth0
192.168.1.64     192.168.254.225  255.255.255.192  UG    0      0        
0 eth0
192.168.1.128    192.168.254.225  255.255.255.128  UG    0      0        
0 eth0
169.254.0.0      0.0.0.0          255.255.0.0      U     0      0        
0 eth2
0.0.0.0          192.168.254.241  0.0.0.0          UG    0      0        
0 eth1

--
Mitja


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