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Old 04-26-2012, 11:10 AM   #1
sam_nyc
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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??
 
Old 04-26-2012, 01:02 PM   #2
MensaWater
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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
 
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Old 04-26-2012, 01:04 PM   #3
sibe
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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.
 
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Old 04-26-2012, 02:50 PM   #4
sam_nyc
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Thank you so much for the info.
 
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