Linux – How to see on Linux what network interface and source IP address is used for a route to a specific destination host

linuxlinux-networkingnetworking

If I have multiple network interfaces (here: 2) on a Linux machine (here: Debian Lenny).
How do I see, over what network interface (NIC) a route to a specific destination host is going and what source IP address is used by default?

I have though of using

ping -I nic1 desthost.example.com
ping -I nic2 desthost.example.com

too see if both ways are possible. (Here: Both ways are possible)

I looked up the routing table

ip route show

But it's quite complex, so I thought, there must by a small simple tool, to just tell me:

"To destination host desthost.example.com it takes interface nicX and source IP address 10.0.0.1"

What is the simplest way of getting this information?

(And I'd rather not use tcpdump and set the interfaces in promiscous mode.)

Thanks.

Best Answer

Use ip route get <ip>.

Related Solutions

Linux – Howto create redundant network on server

In Linux, this is called a bonded ethernet interface.

The steps here are for Red Hat Linux and hopefully will be similar for other Linux distributions:

Step 1. Create bond0 - ethernet card

#vi /etc/sysconfig/network-script/ifcfg-bond0

DEVICE=bond0
USERCTL=no
BOOTPROTO=none
IPADDR=X.X.X.X
NETMASK=255.255.255.0 
GATEWAY=X.X.X.X
TYPE=Ethernet

Step 2. /etc/sysconfig/network-script/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=none
MASTER=bond0
SALAVE=yes
USERCTL=no

Step 3. /etc/sysconfig/network-script/ifcfg-eth1

DEVICE=eth1
BOOTPROTO=none
MASTER=bond0
SALAVE=yes
USERCTL=no

Step 4 /etc/modprobe.conf

alias bond bonding
options bond0  mode=1 miimon=100

mode=1 means active/passive, and miimon=100 millisecond ping or checks for update.

Step 5. Restart the service.

Linux – How to set network interface affinity under Ubuntu Linux

This seems like a situation where you might need to take one step back and let us know in a more general way what you are trying to accomplish, rather then how to implement a particular solution.

That being said, in order to set a process bound to a specific interface in Linux you need to hack the bind system call (man 2 bind). You can do this by using alternative libraries and pre-loading them, see How to use different network interfaces for different processes over on Super User.

Best Answer

Related Solutions

Linux – Howto create redundant network on server

Linux – How to set network interface affinity under Ubuntu Linux

Related Topic