On 08/21/2017 05:03 PM, Gene Heskett wrote: > On Monday 21 August 2017 09:08:11 Christian Seiler wrote: >> 2. Can't add multiple IP addresses to the same interface and >> (worse) even if multiple IP addresses are assigned to the >> same interfaces it only shows the primary address > > I don't know as to how ifconfig sets it up, but its a piece of cake to > edit /etc/network/interfaces to do that. If I bring in a new router, I > uncomment this stanza in the interfaces file: > ================ > #auto eth0:1 > > # to access reset to 192.168.0.1 routers/switches on the 2nd cat5 port > #iface eth0:1 inet static > #address 192.168.0.3 > #netmask 255.255.255.0 > ============== > giving me an address I can use to talk to and configure the new router.
Yeah, that's the old way of doing this via an alias interface. I was talking about the new-style way of doing so though. For example: auto eth0 iface eth0 inet static address 192.168.0.1/24 address 192.168.0.42/24 address 10.5.6.7/8 This will work, and it will assign all IPs to the interface (the first one being the primary and the source IP of outgoing packets where the program doesn't explicitly bind anything). And "ip a" will show all three addresses, but "ifconfig -a" will only show the first. Alias interfaes are kind of legacy, and while they still work, they do have a couple of drawbacks: they aren't really an own interface because they share options with the interface they are based on (which can be confusing if you want to change interface options), there is no way to automatically add a new IP to a given interface without probing first which aliases have already been "used up", the alias namespace is limited by both the max length of an interface name and the limitation of the alias part itself. But don't get me wrong: if it works for you with alias interfaces, I'm certainly not going to tell you to change that - because those also do work with the "ip" utility. The major issue I "ifconfig" has here is that it doesn't see the additional IP addresses of interfaces added by other tools - so that when you rely on ifconfig you _don't_ see the actual entire network configuration of the system, but only a part of it. So it's actually counter-productive when you're troubleshooting a system. >> (2) is really bad, especially the part where it does not show >> all of the IPs that were assigned by other tools, for example > > Huh? ifconfig doesn't even need a -a option to show me eth0:1 if ts > configured and up. Yes, for alias interfaces it does. For the additional IPs added to the interface itself it doesn't. >> NetworkManager, or Debian's own ifupdown via >> /etc/network/interfaces. > > Please don't equate those two. I was talking about how these configure multiple IPs when you use them. Both use the newer kernel interface that allows you to specify multiple IPs on the same interface, while ifconfig uses the old interface that assumes a single IP per interface. And I just used the most prominent programs in Debian as examples for this, but all other management tools I know of (conman, systemd-networkd, ...) also use the newer interface. I really didn't want to discuss the merits or problems of each individual software package. Regards, Christian
