LinuxQuestions.org - [SOLVED] interface question netstat -rn

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interface question netstat -rn

Hi,

Using CentOS, when I do netstat -rn, I see 169 address. I am not sure what that is. Please advice.

Code:

# netstat -rn

Kernel IP routing table

Destination    Gateway        Genmask        Flags  MSS Window  irtt Iface

170.129.83.0    0.0.0.0        255.255.255.0  U        0 0          0 eth0

170.129.83.0    0.0.0.0        255.255.255.0  U        0 0          0 eth1

169.254.0.0    0.0.0.0        255.255.0.0    U        0 0          0 eth1

0.0.0.0        170.129.83.1  0.0.0.0        UG        0 0          0 eth0

On the other servers I have, I don't see any thing for 169 address??

It is a link-local subnet that can be safely ignored.

For more information have a look at the RFC:
http://tools.ietf.org/html/rfc3927

Hi,

169.254.0.0/16 is a special block reserved by IANA for communication between hosts within a subnet in the absence of external address configuration. These addresses are used for address autoconfiguration, a.k.a Zeroconf; when a host can't obtain an IP from static configuration or DHCP server, it can optionally assign itself a link-local IP address of 169.254.x.x/16 and discover services such as printers and file shares without any special configuration.

RFC5735 defines this block are only valid on-link (point-to-point and local network segment).

RFC3927 defines these addresses can't be the source or destination of packets traversing beyond routers, that any device receiving such a packet must not forward it, and any device must not answer all ARP requests for addresses in the 169.254/16 prefix. This restriction applies to multicast packets as well.

The implementation of this standard may vary; Microsoft APIPA, Apple's Bonjour and Unix/Linux Avahi are the wellknown examples.

Many people consider this zero-configuration "feature" is also opening a new hole on the system; tends to do more harm than good, and prefer to disable it entirely. In CentOS, you can disable it by adding the line below to /etc/sysconfig/network :

NOZEROCONF=yes

and restart your network service.

Thank you so much for the info.