Re: Networking - CARP interfaces

On 14 Jun 2011, at 19:33, Steve Polyack <korvus@comcast.net> wrote:

> On 06/14/2011 01:00 PM, Damien Fleuriot wrote:
>>=20
>> I can confirm that this scenario causes problems, see below:
>>=20
>> ### ON FIREWALL 1 , carp master for carp0, carp1, carp2
>> carp2: flags=3D49<UP,LOOPBACK,RUNNING>  metric 0 mtu 1500
>>    inet 192.168.224.254 netmask 0xffffff00
>>    carp: MASTER vhid 224 advbase 1 advskew 50
>>=20
>>=20
>> ### ON FIREWALL 2 , carp backup for carp0, carp1, carp2
>> carp2: flags=3D49<UP,LOOPBACK,RUNNING>  metric 0 mtu 1500
>>    inet 192.168.234.254 netmask 0xffffff00
>>    carp: BACKUP vhid 234 advbase 1 advskew 100
>>=20
>>=20
>> Now, I add a dummy IP to carp2 on FIREWALL 2, which is supposedly backup:=

>>=20
>> ifconfig carp2 inet 192.168.234.207 alias
>>=20
>> Result:
>>=20
>> ### ON FIREWALL 1, carp master for carp0, carp1, carp2
>> carp2: flags=3D49<UP,LOOPBACK,RUNNING>  metric 0 mtu 1500
>>    inet 192.168.224.254 netmask 0xffffff00
>>    carp: MASTER vhid 224 advbase 1 advskew 50
>>=20
>> ### ON FIREWALL 2, carp backup for carp0, carp1, but no longer carp2
>> carp2: flags=3D49<UP,LOOPBACK,RUNNING>  metric 0 mtu 1500
>>    inet 192.168.234.254 netmask 0xffffff00
>>    inet 192.168.234.207 netmask 0xffffff00
>>    carp: MASTER vhid 234 advbase 1 advskew 100
>>   =20
>>   =20
>> After I remove the extraneous IP, the interface becomes backup again:
>>=20
>>=20
>> # This was a long time ago
>> carp0: MASTER ->  BACKUP (more frequent advertisement received)
>> carp0: link state changed to DOWN
>> carp2: MASTER ->  BACKUP (more frequent advertisement received)
>> carp2: link state changed to DOWN
>> carp1: MASTER ->  BACKUP (more frequent advertisement received)
>> carp1: link state changed to DOWN
>> carp2: link state changed to DOWN
>> # This was when I ran my tests
>> carp2: INIT ->  MASTER (preempting)
>> carp2: link state changed to UP
>> carp2: MASTER ->  BACKUP (more frequent advertisement received)
>> carp2: link state changed to DOWN
>=20
> Did you give this enough time to reasonably settle?  Sometimes when the in=
terfaces initially come up, they will become MASTER for a bit before backing=
 down.
>=20

I think I did but I can do try again tomorrow evening just to make sure.

Oh god, if only dmesg entries were timestamped...

>> This entails that hosts in a given carp vhid must have the exact same IP
>> addresses configured on that interface.
>>=20
>> While this is perfectly understandable in a master-backup scenario, this
>> is a bit more annoying for us in a master-backup + backup-backup
>> scenario with 2 datacenters.
>>=20
>> I'll just have to adapt and ensure they have the same IP addresses then.
>=20
> I have a suspicion that the important part may be the number of IP address=
es on the CARP interface.  If CARP sends an advertisement from each IP alias=
 on a CARP interface, then I think that would explain what you are seeing - a=
nd also possibly give you a workaround by adding two more bogus IPs on your p=
rimary datacenter firewalls (where IPs W and Z are normally missing).
>=20
> - Steve
>=20

I'll give it a try, although I think in a scenario where the carp interfaces=
 have the same number of IPs and these IPs differ, both interfaces will clai=
m mastership.

Will post results.=
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