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What does routing an IP address mean?

What does the notation F0/0 and F0/1 mean in this diagram?Intra and internetwork routingWhen/Why to use OSPF?netstat -nr returning “0/1” — what does that mean?How does Logical Address works?How is anycast implemented?Should I always use “no ip address” command?Very confused with routingWhat is the use-case of including the IPv4 address in IPv6 address?Are the IPv6 address space and IPv4 address space completely disjoint?

7

From https://stackoverflow.com/a/40189197/156458

Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed.

What does "routing" a IP address mean?

Why is it the reason that blocking 0.0.0.0 does not make sense?

Thanks.

routing ip-address

share|improve this question

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  You route packets, not addresses. The packets are routed based on the destination address in the packet header. The 0.0.0.0 address (actually, any address in the 0.0.0.0/8 network) is not allowed to be a destination address, so explicitly blocking that address doesn't really make sense.
  
  – Ron Maupin♦
  Mar 23 at 18:57
  

  
  
  
  

add a comment | 

7

From https://stackoverflow.com/a/40189197/156458

Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed.

What does "routing" a IP address mean?

Why is it the reason that blocking 0.0.0.0 does not make sense?

Thanks.

routing ip-address

share|improve this question

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  You route packets, not addresses. The packets are routed based on the destination address in the packet header. The 0.0.0.0 address (actually, any address in the 0.0.0.0/8 network) is not allowed to be a destination address, so explicitly blocking that address doesn't really make sense.
  
  – Ron Maupin♦
  Mar 23 at 18:57
  

  
  
  
  

add a comment | 

From https://stackoverflow.com/a/40189197/156458

Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed.

What does "routing" a IP address mean?

Why is it the reason that blocking 0.0.0.0 does not make sense?

Thanks.

routing ip-address

share|improve this question

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

share|improve this question

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

share|improve this question

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

edited Mar 23 at 17:58

Zac67

35.1k22572

edited Mar 23 at 17:58

Zac67

35.1k22572

asked Mar 23 at 15:47

TimTim

740519

asked Mar 23 at 15:47

TimTim

740519

1 Answer
1

active

oldest

votes

6

"Routing" means forwarding a packet based on its network-layer destination address, usually IPv4 or IPv6.

Routing is done by comparing the destination address to the entries in the local routing table and using the best (=longest prefix) match. The entry contains the next-hop gateway or the interface that the packet is then sent to/out of.

0.0.0.0/0 is the default route - because the prefix has zero length it matches any address. However, it is only selected when no other routing entry matches.

As IP address, 0.0.0.0 generally cannot be used (except as source address when configuring an interface, such as with DHCP).

share|improve this answer

edited Mar 23 at 16:43

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. Does 0.0.0.0 (as an IP address) have two completely different meanings? (1) A process specifies its own unknown address to another process not in the same host, e.g. the DHCP example, and (2) a process specifies that it is listening on all the addresses on the local host, e.g. netstat shows mysql server is listening at ::mysql (unix.stackexchange.com/q/508009/674)?
  
  – Tim
  Mar 23 at 16:42
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In "Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed", does 0.0.0.0 mean a IP address? Why is it never routed?
  
  – Tim
  Mar 23 at 16:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, 0.0.0.0 is also used when specifying "all local IP addresses" when allocating a BSD-style socket - however, this is host-specific and thus off-topic here.
  
  – Zac67
  Mar 23 at 16:46
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can't use 0.0.0.0 as destination address - so it's never routed.
  
  – Zac67
  Mar 23 at 16:56
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. When a server uses 0.0.0.0 to indicate it is listening at all the IP adresses of local host, is 0.0.0.0 used as source address, destination address, or neither?
  
  – Tim
  Mar 23 at 21:46
  

  
  
  
  

 | 
show 4 more comments

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6

"Routing" means forwarding a packet based on its network-layer destination address, usually IPv4 or IPv6.

Routing is done by comparing the destination address to the entries in the local routing table and using the best (=longest prefix) match. The entry contains the next-hop gateway or the interface that the packet is then sent to/out of.

0.0.0.0/0 is the default route - because the prefix has zero length it matches any address. However, it is only selected when no other routing entry matches.

As IP address, 0.0.0.0 generally cannot be used (except as source address when configuring an interface, such as with DHCP).

share|improve this answer

edited Mar 23 at 16:43

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. Does 0.0.0.0 (as an IP address) have two completely different meanings? (1) A process specifies its own unknown address to another process not in the same host, e.g. the DHCP example, and (2) a process specifies that it is listening on all the addresses on the local host, e.g. netstat shows mysql server is listening at ::mysql (unix.stackexchange.com/q/508009/674)?
  
  – Tim
  Mar 23 at 16:42
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In "Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed", does 0.0.0.0 mean a IP address? Why is it never routed?
  
  – Tim
  Mar 23 at 16:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, 0.0.0.0 is also used when specifying "all local IP addresses" when allocating a BSD-style socket - however, this is host-specific and thus off-topic here.
  
  – Zac67
  Mar 23 at 16:46
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can't use 0.0.0.0 as destination address - so it's never routed.
  
  – Zac67
  Mar 23 at 16:56
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. When a server uses 0.0.0.0 to indicate it is listening at all the IP adresses of local host, is 0.0.0.0 used as source address, destination address, or neither?
  
  – Tim
  Mar 23 at 21:46
  

  
  
  
  

 | 
show 4 more comments

6

"Routing" means forwarding a packet based on its network-layer destination address, usually IPv4 or IPv6.

Routing is done by comparing the destination address to the entries in the local routing table and using the best (=longest prefix) match. The entry contains the next-hop gateway or the interface that the packet is then sent to/out of.

0.0.0.0/0 is the default route - because the prefix has zero length it matches any address. However, it is only selected when no other routing entry matches.

As IP address, 0.0.0.0 generally cannot be used (except as source address when configuring an interface, such as with DHCP).

share|improve this answer

edited Mar 23 at 16:43

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. Does 0.0.0.0 (as an IP address) have two completely different meanings? (1) A process specifies its own unknown address to another process not in the same host, e.g. the DHCP example, and (2) a process specifies that it is listening on all the addresses on the local host, e.g. netstat shows mysql server is listening at ::mysql (unix.stackexchange.com/q/508009/674)?
  
  – Tim
  Mar 23 at 16:42
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In "Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed", does 0.0.0.0 mean a IP address? Why is it never routed?
  
  – Tim
  Mar 23 at 16:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, 0.0.0.0 is also used when specifying "all local IP addresses" when allocating a BSD-style socket - however, this is host-specific and thus off-topic here.
  
  – Zac67
  Mar 23 at 16:46
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can't use 0.0.0.0 as destination address - so it's never routed.
  
  – Zac67
  Mar 23 at 16:56
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks. When a server uses 0.0.0.0 to indicate it is listening at all the IP adresses of local host, is 0.0.0.0 used as source address, destination address, or neither?
  
  – Tim
  Mar 23 at 21:46
  

  
  
  
  

 | 
show 4 more comments

"Routing" means forwarding a packet based on its network-layer destination address, usually IPv4 or IPv6.

Routing is done by comparing the destination address to the entries in the local routing table and using the best (=longest prefix) match. The entry contains the next-hop gateway or the interface that the packet is then sent to/out of.

0.0.0.0/0 is the default route - because the prefix has zero length it matches any address. However, it is only selected when no other routing entry matches.

As IP address, 0.0.0.0 generally cannot be used (except as source address when configuring an interface, such as with DHCP).

share|improve this answer

edited Mar 23 at 16:43

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

share|improve this answer

edited Mar 23 at 16:43

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572

answered Mar 23 at 16:33

Zac67Zac67

35.1k22572