Configuring logical interfaces in solaris

In this short article I'll walk you through the steps involved in configuring a logical interface on a Solaris system.
Logical interfaces come in handy when we need to assign multiple IP addresses to a single physical NIC card. This technique was especially useful while configuring zones on Solaris 10. with Solaris 11 the network stack was significantly re-written and we don't really use logcial interfaces for zones on our Solaris 11 systems.

First we plumb the interface:

root@sandbox:/# ifconfig e1000g0:1 plumb

The plumb argument with the ifconfig command makes the interface corresponding to the physical device/ NIC card available for TCP/IP communication.

Let's see if we can see it in ifconfig:

root@sandbox:/# ifconfig e1000g0:1
e1000g0:1: flags=1000842<BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
        inet 0.0.0.0 netmask 0

The interface is available but is in a down state and carries no network traffic.

Now, we assign an IP address to it and bring it up:

root@sandbox:/# ifconfig e1000g0:1 192.168.87.142 netmask 255.255.255.0 up

The ifconfig command now shows that an IP has been assigne dto the interface and it is up.

root@sandbox:/# ifconfig e1000g0:1

e1000g0:1: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2

        inet 192.168.87.142 netmask ffffff00 broadcast 192.168.87.255

To make the addition persistent across reboots we need to create a file /etc/hostname.interface name and add the IP address assigned to the interface in that file as shown below:

root@sandbox:/# echo 192.168.87.142 >> /etc/hostname.e1000g0:1

root@sandbox:/# cat /etc/hostname.e1000g0:1

192.168.87.142

Now, to verify that the logical interface is functioning correctly, we ping google.com through it.

root@sandbox:/# ping -i e1000g0:1 google.com

google.com is alive

As a final test we try to ssh to the host and check if snoop can pick on the traffic.

[user.DESKTOP-4NN)77O] ➤ ssh root@192.168.87.142

Last login: Sun Oct  1 15:51:32 2017 from 192.168.87.1

Sun Microsystems Inc.   SunOS 5.10      Generic January 2005

root@sandbox:/#

Snoop will not be able to capture packets on the logical interface because it does not have an underlying data link component. So I ran snoop on the underlaying interface e1000g0 and it did capture traffic for the logical interface e1000g0:1.

root@sandbox:/# snoop -d e1000g0

Using device e1000g0 (promiscuous mode)

     sandbox -> 192.168.87.1 TCP D=63292 S=22 Push Ack=2221229257 Seq=382012030 Len=32 Win=49640

192.168.87.1 -> sandbox      TCP D=22 S=63292 Ack=382012062 Seq=2221229257 Len=0 Win=2052

     sandbox -> 192.168.87.2 DNS C 1.87.168.192.in-addr.arpa. Internet PTR ?

192.168.87.2 -> (broadcast)  ARP C Who is 192.168.87.141, sandbox ?

     sandbox -> 192.168.87.2 ARP R 192.168.87.141, sandbox is 0:c:29:59:30:b0

192.168.87.2 -> sandbox      DNS R  Error: 3(Name Error)

     sandbox -> 192.168.87.2 DNS C 1.87.168.192.in-addr.arpa. Internet PTR ?

192.168.87.2 -> sandbox      DNS R  Error: 3(Name Error)

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Push Ack=454369125 Seq=3517627341 Len=32 Win=2050

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Push Ack=3517627373 Seq=454369125 Len=48 Win=49640

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Push Ack=3517627373 Seq=454369173 Len=48 Win=49640

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Push Ack=3517627373 Seq=454369221 Len=64 Win=49640

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Ack=454369285 Seq=3517627373 Len=0 Win=2050

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Push Ack=454369285 Seq=3517627373 Len=32 Win=2050

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Push Ack=454369285 Seq=3517627405 Len=64 Win=2050

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Ack=3517627469 Seq=454369285 Len=0 Win=49640

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Fin Ack=454369285 Seq=3517627469 Len=0 Win=2050

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Ack=3517627470 Seq=454369285 Len=0 Win=49640

192.168.87.142 -> 192.168.87.1 TCP D=63545 S=22 Fin Ack=3517627470 Seq=454369285 Len=0 Win=49640

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63545 Ack=454369286 Seq=3517627470 Len=0 Win=2050

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63550 Fin Ack=455480447 Seq=2920316502 Len=0 Win=2052

192.168.87.142 -> 192.168.87.1 TCP D=63550 S=22 Ack=2920316503 Seq=455480447 Len=0 Win=49640

192.168.87.142 -> 192.168.87.1 TCP D=63550 S=22 Fin Ack=2920316503 Seq=455480447 Len=0 Win=49640

192.168.87.1 -> 192.168.87.142 TCP D=22 S=63550 Ack=455480448 Seq=2920316503 Len=0 Win=2052