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Old 06-18-2009, 02:31 AM   #1
your_shadow03
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Understanding iproute2 Deeply?


I have been reading this more carefully:
Code:
[ahu@home ahu]$ ip address show        
1: lo: <LOOPBACK,UP> mtu 3924 qdisc noqueue 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
2: dummy: <BROADCAST,NOARP> mtu 1500 qdisc noop 
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
3: eth0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1400 qdisc pfifo_fast qlen 100
    link/ether 48:54:e8:2a:47:16 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.1/8 brd 10.255.255.255 scope global eth0
4: eth1: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 100
    link/ether 00:e0:4c:39:24:78 brd ff:ff:ff:ff:ff:ff
3764: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP> mtu 1492 qdisc pfifo_fast qlen 10
    link/ppp 
    inet 212.64.94.251 peer 212.64.94.1/32 scope global ppp0

Let's examine eth0 somewhat closer. It says that it is related to the inet address '10.0.0.1/8'. What does this mean? The /8 stands for the number of bits that are in the Network Address. There are 32 bits, so we have 24 bits left that are part of our network. The first 8 bits of 10.0.0.1 correspond to 10.0.0.0, our Network Address, and our netmask is 255.0.0.0.
Now the last two lines:
Code:
The other bits are connected to this interface, so 10.250.3.13 is directly available on eth0, as is 10.0.0.1 for example.
What does the last two lines << 10.250.3.13>> mean?

Last edited by your_shadow03; 06-18-2009 at 02:33 AM.
 
Old 06-18-2009, 02:58 AM   #2
billymayday
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That IPs 10.0.0.0 to 10.255.255.255 will be accessed through eth0 as per (3) since it is 10.0.0.0/8
 
Old 06-18-2009, 03:33 AM   #3
your_shadow03
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Thats Ok but what does this means:
Code:
The other bits are connected to this interface, so 10.250.3.13 is directly available on eth0, as is 10.0.0.1 for example.
 
Old 06-18-2009, 04:13 AM   #4
billymayday
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I thought that's what I'd answered.

Think of an IP as:

bis 0-7. bits 8-15. bits 16-23. bits 24-31

Therefore an IP range 10.0.0.0/8 means everything where the 8 most significant bits are 10 (ie bits 0-7), so the patterns

00001010.00000000.00000000.00000000 to 00001010.11111111.11111111.11111111

or

10.0.0.0 to 10.255.255.255 in decimal notation.

are connected to eth0 (the "other bits" referring to the bit patterns in the 2nd, 3rd and 4th positions).

Does that explain it?
 
  


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