Mailing List Archive

On Fri, 14 May 2021, Jim Pazarena via Exim-users wrote:

> I have a server with three IP numbers of the same subnet . my smtp transport
> specifies the specific outbound IP number .
> Yet other servers complain of an ssl mis-match because they are seeing one of
> the other IPs which are not in the " interface = " line .

If you have seperate names for these addresses, setting
primary_hostname
may help.

> Is there an easy way to determine how this may be happening ?

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Andrew C. Aitchison Kendal, UK
andrew@aitchison.me.uk

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On 15/05/2021 06:55, Jim Pazarena via Exim-users wrote:
> a server with three IP numbers of the same subnet

Generally a bad move. Unless the networks are physically
separated, IP routing just gets confused.

Fix your network design.
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Cheers,
Jeremy

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Hi Jim,

Jim Pazarena via Exim-users <exim-users@exim.org> (Sa 15 Mai 2021 07:55:24 CEST):
> I have a server with three IP numbers of the same subnet . my smtp transport
> specifies the specific outbound IP number .
> Yet other servers complain of an ssl mis-match because they are seeing one
> of the other IPs which are not in the " interface = " line .

They complain about SSL mis-matches? Do you use SSL client certificates?
Best would be if you can do a tcpdump on your physical interface having
the 3 IP addresses.

--
Heiko

On Sat, 15 May 2021, Jeremy Harris via Exim-users wrote:

> On 15/05/2021 06:55, Jim Pazarena via Exim-users wrote:
>> a server with three IP numbers of the same subnet
>
> Generally a bad move. Unless the networks are physically
> separated, IP routing just gets confused.
>
> Fix your network design.

Hmm.

I know that Linux networking has changed since the days of Red Hat
Enterprise Linux 4, 5 and 6, but I didn't have problems running
a machine IP and a service IP on the same physical interface of
each of my servers a decade ago.

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Andrew C. Aitchison Kendal, UK
andrew@aitchison.me.uk

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On Sat, May 15, 2021 at 11:11:40AM +0100, Jeremy Harris via Exim-users wrote:
> On 15/05/2021 06:55, Jim Pazarena via Exim-users wrote:
> > a server with three IP numbers of the same subnet
>
> Generally a bad move. Unless the networks are physically
> separated, IP routing just gets confused.

No, ip routing is fine with multiple ip addresses on the same network.
However, advanced sysadmin skills are required to configure it properly.

Multiple ip addresses may be used to select different outgoing channels
if host is placed behind a device doing src-based policy routing.

In recent Linux kernels not multiple IPs, but even multiple MACs on
the same interface are possible.
--
Eugene Berdnikov

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