netdev - Re: Configure ICMP error source address

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Date:	Fri, 08 Jan 2016 10:24:48 -0500
From:	prmarino1@...il.com
To:	Robert Sander <r.sander@...nlein-support.de>,
	netfilter@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Configure ICMP error source address

Don't put a public address on a lo device use a dummy eth interface instead‎. Any IP address and it's subnet assigned to a lo device is  marked as a marcian address and the traffic is dropped if it tries to leave the lo device.

I know that there is som old documentation out there (for example quagga's documentation) that says you can do it ‎but it's been wrong since the 2.4 version off the kernel. 
Linux treats the lo device differently that what routers call a loopback device. The dummy driver is the linux equivalent of what routers call a loopback device.
  Original Message  
From: Robert Sander
Sent: Friday, January 8, 2016 04:32
To: netfilter@...r.kernel.org; netdev@...r.kernel.org
Subject: Configure ICMP error source address

Hi,

It is possible to change the source address of ICMP error messages
generated by the kernel via
/proc/sys/net/ipv4/icmp_errors_use_inbound_ifaddr. This is currently the
only way to influence the source address as ICMP errors do not travel
through the NAT table (for obvious reasons).

We have the situation that our routers use RFC1918 addresses on their
transfer networks (which should be quite common nowadays to save on
public IPv4 addresses). ICMP errors are generated with RFC1918 source
addresses and therefor never reach the original sender.

Every router has its public IP address bound to dev lo to be reachable
even if any one interface is down. Routing protocols assure that.

Is it a good idea to develop a kernel patch that makes it possible to
select the first IPv4 address on dev lo with scope global as the source
address for ICMP errors? Would that do any harm to the Internet at large?

Regards
-- 
Robert Sander
Heinlein Support GmbH
Schwedter Str. 8/9b, 10119 Berlin

http://www.heinlein-support.de

Tel: 030 / 405051-43
Fax: 030 / 405051-19

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Geschäftsführer: Peer Heinlein -- Sitz: Berlin