Re: Sending ICMP echo request out

anil dahiya <[email protected]> Fri, 9 Dec 2011 00:00:04 +0530
Newsgroups gmane.linux.newbie,gmane.comp.security.firewalls.netfilter.general,gmane.linux.network.general
Message-ID <CAHGPgw1bL7XF6Ef29N_YQ-dAW3RYQe7j4-2zuWhFXQddW+Yg_g@mail.gmail.com> 
Hi ,

I have following setup with routing table as shown below:

+-----------------------+
|=A0=A0=A0 System-1      |
|=A0=A0=A0=A0 "client"=A0=A0=A0      |
|------------------------|
|=A0=A0192.168.11.5=A0=A0=A0|
+----------------------+
=A0=A0=A0=A0=A0=A0 |
=A0=A0=A0=A0=A0=A0 |
+------+-----+
|=A0=A0=A0Switch =A0=A0+----------------------+
+------+-----+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0   |
=A0=A0=A0=A0=A0=A0 |=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0      |
 =A0=A0=A0=A0=A0=A0|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0   =A0=
=A0=A0=A0=A0+-------------------------+
=A0=A0=A0=A0=A0=A0 | =A0 =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0   =A0=
=A0  |=A0=A0192.168.11.1=A0=A0=A0=A0=A0 |
=A0 =A0 =A0=A0=A0|=A0=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=A0     |------=
---------------------|
  =A0 =A0=A0=A0|=A0=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=A0     | =A0 =A0=
 Router =A0 =A0 =A0 =A0    |
=A0 =A0 =A0=A0=A0|=A0=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=A0     |------=
-------------------- |
=A0=A0=A0=A0=A0=A0=A0|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0    |=A0=A0=A0192.168.12.1=A0=A0=A0=A0 |
=A0=A0=A0=A0=A0=A0=A0|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0    +--------------------------+
=A0 =A0 =A0=A0=A0|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0     =A0 =A0 =A0=A0 =A0  =A0|
 =A0=A0=A0=A0=A0 |=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0=A0=A0=A0=A0=A0      =A0=A0   |
+------------------------+=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0  |
|=A0=A0192.168.11.6=A0=A0=A0=A0=A0 |=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
=A0=A0  |
|--------------------------|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=
 |
| =A0 System-2=A0 =A0=A0=A0=A0=A0 |=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=
  =A0=A0|
|--------------------------| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
|=A0=A0=A0192.168.12.6 =A0=A0=A0|=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0  =
=A0 |
|                         =A0|----------------+
+------------------------+

Routing table details of setup
------------------------------------------
System-1
-----
$route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use=
 Iface
192.168.11.0    0.0.0.0         255.255.255.0   U     1      0        0=
 eth1
0.0.0.0         192.168.11.1    0.0.0.0         UG    0      0        0=
 eth1


Router
-----------
$route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use=
 Iface
192.168.12.0    0.0.0.0         255.255.255.0   U     0      0        0=
 eth1
192.168.11.0    0.0.0.0         255.255.255.0   U     0      0        0=
 eth0


System-2
------
$route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use=
 Iface
192.168.12.0    0.0.0.0         255.255.255.0   U     0      0        0=
 eth1
192.168.11.0    0.0.0.0         255.255.255.0   U     0      0        0=
 eth0
0.0.0.0         192.168.12.1    0.0.0.0         UG    0      0        0=
 eth1


When I do ping from system-1 192.168.11.5 to system-2 192.168.12.6 ,
ping echo packet is reaching on system-2 through NIC 192.168.12.6 but
system is not sending any response to 192.168.11.5 using either of NIC
i.e 192.168.11.6 or 192.168.12.6 ? Why this is happening ? Can you
help me ?

I have observed same type of symtoms when I do SSH from 192.168.11.5
to 192.168.12.6

=46YI,
ip_forwarding is enable on router and iptables are no configured on
any of system .

Thanks,
Anil
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