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Deleting an alias causes rest to get deleted

DISCUSSION Volkan Yazıcı 4 participants 4 messages Jul 2, 2012 – Jul 3, 2012

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Volkan Yazıcı

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#0 lore raw

Hi!

I observe an IP aliasing anomaly that occurs when I try to delete an IP alias from an interface. That is, when I delete the first address in a set of IP aliased addresses assigned according to a particular subnet, rest of the aliases get deleted as well. Check out the below snippet.

   $ *for I in `seq 1 6`; do sudo ip addr add 192.168.2.$I/29 dev eth0;
   done*
   $ ip addr list
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
   state UP qlen 1000
        link/ether 00:24:54:b9:1c:f8 brd ff:ff:ff:ff:ff:ff
   *inet 192.168.1.200/24 brd 192.168.1.255 scope global eth0**
        inet 192.168.2.1/29 scope global eth0
        inet 192.168.2.2/29 scope global secondary eth0
        inet 192.168.2.3/29 scope global secondary eth0
        inet 192.168.2.4/29 scope global secondary eth0
        inet 192.168.2.5/29 scope global secondary eth0
        inet 192.168.2.6/29 scope global secondary eth0*
        inet6 fe80::224:54ff:feb9:1cf8/64 scope link
           valid_lft forever preferred_lft forever
   3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
        link/ether e8:39:df:6a:21:2a brd ff:ff:ff:ff:ff:ff
   $ *sudo ip addr del 192.168.2.1/29 dev eth0*
   $ ip addr list
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
   state UP qlen 1000
        link/ether 00:24:54:b9:1c:f8 brd ff:ff:ff:ff:ff:ff
   *inet 192.168.1.200/24 brd 192.168.1.255 scope global eth0*
        inet6 fe80::224:54ff:feb9:1cf8/64 scope link
           valid_lft forever preferred_lft forever
   3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
        link/ether e8:39:df:6a:21:2a brd ff:ff:ff:ff:ff:ff

Per see, deleting 192.168.2.1/29 causes the rest of the aliased interfaces get deleted as well. This is something that is slightly documented in the ifconfig manual: /for every scope (i.e. same net with address/netmask combination) all aliases are deleted, if you delete the first (primary)/. So what is the right way of just deleting the first (primary) alias without affecting the rest? If this is a scoping issue, is it possible to assign each alias as primary within its own dedicated scope?

As a side note, when I first asked this question to Stephen Hemminger (he forwarded me to this mailing list) he also told me that "/In Linux the interface aliases are really a legacy from the BSD style addressing, and don't act the same. It is not common practice to use them./" Is that really the case? Because, as you know, IP aliasing is the heart of a majority of the high-availability and clustering solutions in Linux. Is IP aliasing a really deprecated technology in Linux? Should we avoid using it? If so, what do you recommend as an alternative?

Best.

#1 lore raw
Quoted 6 lines · Volkan Yazıcı

Hi!

I observe an IP aliasing anomaly that occurs when I try to delete an IP alias from an interface. That is, when I delete the first address in a set of IP aliased addresses assigned according to a particular subnet, rest of the aliases get deleted as well. Check out the below snippet.

[...]

Quoted 5 lines

As a side note, when I first asked this question to Stephen Hemminger (he forwarded me to this mailing list) he also told me that "/In Linux the interface aliases are really a legacy from the BSD style addressing, and don't act the same. It is not common practice to use them./" Is that really the case?

[...]

If you didn't give him the full details shown above, it's possible he thought you meant alias interfaces such as 'eth0:0'.

Ben.

Signature · 3 lines
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
#2 lore raw
Quoted 13 lines · On Tue, 3 Jul 2012 02:12:17 +0100 Ben Hutchings <[email protected]>…
Quoted 6 lines · Volkan Yazıcı

Hi!

I observe an IP aliasing anomaly that occurs when I try to delete an IP alias from an interface. That is, when I delete the first address in a set of IP aliased addresses assigned according to a particular subnet, rest of the aliases get deleted as well. Check out the below snippet.

[...]

Quoted 5 lines

As a side note, when I first asked this question to Stephen Hemminger (he forwarded me to this mailing list) he also told me that "/In Linux the interface aliases are really a legacy from the BSD style addressing, and don't act the same. It is not common practice to use them./" Is that really the case?

Quoted 4 lines

[...]

If you didn't give him the full details shown above, it's possible he thought you meant alias interfaces such as 'eth0:0'.

Yes, that is what I was assuming by the word 'alias'

#3 lore raw
In reply to Volkan Yazıcı

Hello,

Quoted 6 lines · Volkan Yazıcı

Hi!

I observe an IP aliasing anomaly that occurs when I try to delete an IP alias from an interface. That is, when I delete the first address in a set of IP aliased addresses assigned according to a particular subnet, rest of the aliases get deleted as well. Check out the below snippet.

This is in Linux may be from the 2.3/2.4 times

Quoted 39 lines
   $ *for I in `seq 1 6`; do sudo ip addr add 192.168.2.$I/29 dev eth0;
   done*
   $ ip addr list
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
   state UP qlen 1000
        link/ether 00:24:54:b9:1c:f8 brd ff:ff:ff:ff:ff:ff
   *inet 192.168.1.200/24 brd 192.168.1.255 scope global eth0**
        inet 192.168.2.1/29 scope global eth0
        inet 192.168.2.2/29 scope global secondary eth0
        inet 192.168.2.3/29 scope global secondary eth0
        inet 192.168.2.4/29 scope global secondary eth0
        inet 192.168.2.5/29 scope global secondary eth0
        inet 192.168.2.6/29 scope global secondary eth0*
        inet6 fe80::224:54ff:feb9:1cf8/64 scope link
           valid_lft forever preferred_lft forever
   3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
        link/ether e8:39:df:6a:21:2a brd ff:ff:ff:ff:ff:ff
   $ *sudo ip addr del 192.168.2.1/29 dev eth0*
   $ ip addr list
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
   state UP qlen 1000
        link/ether 00:24:54:b9:1c:f8 brd ff:ff:ff:ff:ff:ff
   *inet 192.168.1.200/24 brd 192.168.1.255 scope global eth0*
        inet6 fe80::224:54ff:feb9:1cf8/64 scope link
           valid_lft forever preferred_lft forever
   3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
        link/ether e8:39:df:6a:21:2a brd ff:ff:ff:ff:ff:ff
Quoted 7 lines

Per see, deleting 192.168.2.1/29 causes the rest of the aliased interfaces get deleted as well. This is something that is slightly documented in the ifconfig
manual: /for every scope (i.e. same net with address/netmask combination) all aliases are deleted, if you delete the first (primary)/. So what is the right way of just deleting the first (primary) alias without affecting the rest? If this is a scoping issue, is it possible to assign each alias as primary within its own dedicated scope?

There is (yet) undocumented feature for the
interfaces:

/proc/sys/net/ipv4/conf/*/promote_secondaries

You set it for specific interface _or_ for "all".
It defaults to 0. When you enable it, deleting a primary address will not delete all secondary addresses but will change the next secondary as primary. The term alias may refer for addresses on same interface while here the problem is for a subset of addresses - from same subnet. Primary is the first address added for the configured subnet, all next addresses in subnet are added as secondaries as shown by ip addr list.

Quoted 8 lines

As a side note, when I first asked this question to Stephen Hemminger (he forwarded me to this mailing list) he also told me that "/In Linux the interface aliases are really a legacy from the BSD style addressing, and don't act the same. It is not common practice to use them./" Is that really the case? Because, as you know, IP aliasing is the heart of a majority of the high-availability and clustering solutions in Linux. Is IP aliasing a really deprecated technology in Linux? Should we avoid using it? If so, what do you recommend as an alternative?

Please do not stop using aliases!

Regards

--
Julian Anastasov <[email protected]>