Multiple IPv4 addresses per NIC (w/o aliases, VLANs, etc.)

Ken D'Ambrosio ken at jots.org
Mon Sep 17 16:08:14 EDT 2018


So, I didn't know this was "a thing."  And, apparently, "ifconfig" 
doesn't know it, either.  However, with "ip addr add", you can assign 
multiple IPv4 addresses to a given interface:

methusalah # ifconfig tun0
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 1500
         inet 192.168.23.50  netmask 255.255.255.255  destination 
192.168.23.49
         inet6 fe80::6d4d:9731:4512:1f75  prefixlen 64  scopeid 
0x20<link>
         unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
txqueuelen 100
(UNSPEC)
         RX packets 0  bytes 0 (0.0 B)
         RX errors 0  dropped 0  overruns 0  frame 0
         TX packets 9  bytes 432 (432.0 B)
         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

methuselah FAQ # ip addr add 10.20.30.40/32 dev tun0

methuselah FAQ # ip addr show tun0
4: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc 
fq_codel
state UNKNOWN group default qlen 100
     link/none
     inet 192.168.23.50 peer 192.168.23.49/32 scope global tun0
        valid_lft forever preferred_lft forever
     inet 10.20.30.40/32 scope global tun0
        valid_lft forever preferred_lft forever

And yet ifconfig doesn't even show the new info.  Note that this is 
dinstinct from "tun.0" or "tun:0" (VLAN and alias, respectively).

Is the ability to have multiple v4 addresses against a given NIC a new 
feature?  Is it somehow bogus?  Maybe it's an extension of the way that 
v6 works, since v6 has always allowed multiple addresses/NIC -- perhaps 
aliases are deprecated?

Just wondering if anyone else has noticed this...

-Ken



More information about the gnhlug-discuss mailing list