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In Linux, by default, packets are considered individually for routing purposes. Thus, all the routing algorithm determines where to send a packet based on that packet itself, without taking into consideration that the packet may be a response packet of sorts.
In a typical setup, this means that all outgoing traffic is going out over one interface, say, eth0 even if the incoming packet was sent to interface eth1.
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One typical side effect of this algorithm is creation of so called "martian packets". A martian packet is an IP packet which specifies a source or destination address that is either reserved for special-use by Internet Assigned Numbers Authority (IANA) or does not belong to the subnet on which this interface exists, and that makes no sense. [RFC 1812]. For example, if two interfaces are connected to two subnets of 10 network, and default router is configured for eth0, then without expisit routing statement you can't respond to the packet send to eth1, which is not on the local segment for this network.
In other words, a martian packet header source IP address is usually a IP address that iether:For example, a 127.0.0.0/8 IP address coming through a router, would be labeled as being martian, as such packets should be local only and should not travel via the network.
RFC 1812 defines the term a martian source the following way:
"An IP source address is invalid if it is a special IP address, as defined in 4.2.2.11 or 5.3.7, or is not a unicast address.
"An IP destination address is invalid if it is among those defined as illegal destinations in 4.2.3.1, or is a Class E address (except 255.255.255.255)."A router SHOULD NOT forward any packet that has an invalid IP source address or a source address on network 0. A router SHOULD NOT forward, except over a loop-back interface, any packet that has a source address on network 127. A router MAY have a switch that allows the network manager to disable these checks. If such a switch is provided, it MUST default to performing the checks.
"A router SHOULD NOT forward any packet that has an invalid IP destination address or a destination address on network 0. A router SHOULD NOT forward, except over a loop-back interface, any packet that has a destination address on network 127. A router MAY have a switch that allows the network manager to disable these checks. If such a switch is provided, it MUST default to performing the checks.
"If a router discards a packet because of these rules, it SHOULD log at least the IP source address, the IP destination address, and, if the problem was with the source address, the physical interface on which the packet was received and the link Layer address of the hostor router from which the packet was received."
Martian source is network traffic from the wrong subnet appearing on an interface. For example if:
eth0 has IP 192.168.0.1 on subnet 255.255.255.0 eth1 has IP 192.168.1.1 on subnet 255.255.255.0
This means that eth0 should only see IP traffic from IP addresses from its subnet (192.168.0.x) and eth1 should only see traffic from its subnet (192.168.1.x)
If an IP on the network (say a forgotten printer or something) is still configured with a previous network address (202.167.2.34) and is seen on eth1 it will be seen as martian source.
If one of the machines on the network 192.168.0.x is plugged into the wrong switch and is effectively on the same network segment (physical) as eth1, then you will see martian source from that IP address (or you have multiple networks that the Linux box is not aware of)
Martian source is not a major thing, but such messages help making you aware of the fact that something in your network setup is either setup incorrectly, or not configured optimally.
We observed strange change of behavior between kernel 2.6.16.60-0.54.5-smp and 2.6.16.60-0.68.1-smp (64-bit):
Previously on old kernel (SLES 10 SP3 2.6.16.60-0.54.5-smp) our eth1 interface (backup segment) was reachable from our workstations. With newer kernel (for example 2.6.16.60-0.68.1-smp on SLES 10 SP3) it is not and "martian source" warnings can be found in the log. For example:
Mar 30 16:19:23 nti247 kernel: printk: 2 messages suppressed. Mar 30 16:19:23 nti247 kernel: martian source 10.201.29.247 from 10.194.154.73, on dev eth1
Mar 30 16:19:23 nti247 kernel: ll header: 00:18:8b:30:cd:2f:00:0c:f8:9b:82:0a:08:00
Only SLES server are behaving this way starting from approximately with the kernel version 2.6.16.60-0.68.1 on SLES 10 SP3. Red Hat and Solaris servers on the same segment behave "permissively".
This behavior is controlled by pretty obscure setting in /etc/sysctl.conf
# Controls source route verification net.ipv4.conf.default.rp_filter = 1
You can disable it changing the value to zero (please don't forget to run sysctl -p command to make those settings current).
# Controls source route verification net.ipv4.conf.default.rp_filter = 0
As of April 2012 this fix works for (patched) SLES 10 SP3, SLES 10 SP4 and SLES 11 SP1. Does not work for SLES 11 SP2.
The reasoning behind the strict ingress filtering that is enabled by net.ipv4.conf.default.rp_filter = 1 setting is protection from spoofing of source address (typical for UDP Distributed Denial of Service Attacks).
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Server Fault
I keep getting these messages in /var/log/messages :
Mar 8 23:17:25 saas1 kernel: martian source 169.254.1.1 from 169.254.95.118, on dev usb0 Mar 8 23:17:25 saas1 kernel: ll header: ff:ff:ff:ff:ff:ff:00:21:5e:de:1b:be:08:06Over and over every 5 seconds there's another report exactly the same way.
I did a whois on 169.254.95.118 and get a strange message back also:
http://whois.arin.net/rest/nets;q=169.254.95.118?showDetails=true&showARIN=false
This is the "link local" block. It was set aside for this special use in the Standards Track document, RFC 3927 and was further documented in the Best Current Practice RFC 5735, which can be found at: http://www.rfc-editor.org/rfc/rfc3927.txt http://www.rfc-editor.org/rfc/rfc5735.txt It is allocated for communication between hosts on a single link. Hosts obtain these addresses by auto-configuration, such as when a DHCP server cannot be found. A router MUST NOT forward a packet with an IPv4 Link-Local source or destination address, irrespective of the router's default route configuration or routes obtained from dynamic routing protocols. A router which receives a packet with an IPv4 Link-Local source or destination address MUST NOT forward the packet. This prevents forwarding of packets back onto the network segment from which they originated, or to any other segment.
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On Monday 02 August 2004 08:45, Paolo Santancini wrote:
> Hi all,
> anybody can give me information about the kernel message called "martian
> source" written in "/var/log/messages"??? What does it mean?Martian source is network traffic from the wrong subnet appearing on an
interface.eg. eth0 has IP 192.168.0.1 on subnet 255.255.255.0
eth1 has IP 192.168.1.1 on subnet 255.255.255.0This means that eth0 should only see IP traffic from IP addresses from its
subnet (192.168.0.x) and eth1 should only see traffic from its subnet
(192.168.1.x)If an IP on the network (say a forgotten printer or something) is still
configured with a previous network address (202.167.2.34) and is seen on eth1
it will be seen as martian source.If one of the machines on the network 192.168.0.x is plugged into the wrong
switch and is effectively on the same network segment (physical) as eth1,
then you will see martian source from that IP address (or you have multiple
networks that the Linux box is not aware of)Martian source is not a major thing, but it is making you aware of the fact
that something in your network setup is either setup incorrectly, or not
configured optimally.
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Hi, (minor update) See /usr/src/linux/Documentation/networking/ip-sysctl.txt for an explanation of parameters that can be set for networking, specifically "log_martians". The current settings can be found by typing (as root): sysctl -a | grep martian (if there multiple interfaces their will be an entry for each one net.ipv4.conf.XXXXX.log_martians plus the "default" and "all"). Two way to implement this: 1. From the command line (needs to be re-done each time you reboot): echo 0 >/proc/sys/net/ipv4/conf/all/log_martians echo 0 >/proc/sys/net/ipv4/conf/default/log_martians echo 0 >/proc/sys/net/ipv4/conf/eth1/log_martians 2. Automatically at startup, by editing /etc/sysctl.conf and adding: net.ipv4.conf.default.log_martians = 0 net.ipv4.conf.all.log_martians = 0 To activate the changes without rebooting type: /etc/rc.d/boot.sysctl start echo 0 >/proc/sys/net/ipv4/conf/eth1/log_martians The latter echo is necessary without a reboot as the default setting will only apply when an inteface is brought up. Rgds, Simon -----Original Message----- From: Tarjei Huse [mailto:tarjei+a_lists.suse@xxxxx] Sent: Tuesday, August 02, 2005 12:57 To: suse-security@xxxxxxxx Subject: [suse-security] Martian problems Hi, I'm having problems with a SuSE 9.2 box. The box is set up with two interfaces on the same subnet. The interfaces has been set up as normal with static ip's 10.9.1.3, 10.9.1.2 , netmask 255.255.255.0 and broadcast 10.9.1.255. I'm getting errormessages saying Aug 2 12:33:41 mail2 kernel: martian source 10.9.1.255 from 10.9.1.3, on dev eth1 Aug 2 12:33:41 mail2 kernel: ll header: ff:ff:ff:ff:ff:ff:00:c0:9f:2c:2d:f7:08:00 Is this related to the usage of two nics on the same subnet? If so, is there a way to solve this? It seems the martians are stopping cups from doing broadcasts. Kind regards, Tarjei -- Check the headers for your unsubscription address For additional commands, e-mail: suse-security-help@xxxxxxxx Security-related bug reports go to security@xxxxxxx, not here
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