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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?













6















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



















  • 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♦
    yesterday















6















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



















  • 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♦
    yesterday













6












6








6








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
















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




routing ip-address






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday









Zac67

32k22163




32k22163










asked yesterday









TimTim

613516




613516







  • 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♦
    yesterday












  • 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♦
    yesterday







2




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♦
yesterday





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♦
yesterday










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

























  • 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
    yesterday












  • 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
    yesterday











  • 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
    yesterday











  • You can't use 0.0.0.0 as destination address - so it's never routed.

    – Zac67
    yesterday











  • 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
    yesterday










Your Answer








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1 Answer
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1 Answer
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active

oldest

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active

oldest

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active

oldest

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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

























  • 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
    yesterday












  • 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
    yesterday











  • 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
    yesterday











  • You can't use 0.0.0.0 as destination address - so it's never routed.

    – Zac67
    yesterday











  • 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
    yesterday















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

























  • 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
    yesterday












  • 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
    yesterday











  • 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
    yesterday











  • You can't use 0.0.0.0 as destination address - so it's never routed.

    – Zac67
    yesterday











  • 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
    yesterday













6












6








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















"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














share|improve this answer



share|improve this answer








edited yesterday

























answered yesterday









Zac67Zac67

32k22163




32k22163












  • 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
    yesterday












  • 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
    yesterday











  • 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
    yesterday











  • You can't use 0.0.0.0 as destination address - so it's never routed.

    – Zac67
    yesterday











  • 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
    yesterday

















  • 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
    yesterday












  • 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
    yesterday











  • 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
    yesterday











  • You can't use 0.0.0.0 as destination address - so it's never routed.

    – Zac67
    yesterday











  • 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
    yesterday
















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
yesterday






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
yesterday














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
yesterday





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
yesterday













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
yesterday





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
yesterday













You can't use 0.0.0.0 as destination address - so it's never routed.

– Zac67
yesterday





You can't use 0.0.0.0 as destination address - so it's never routed.

– Zac67
yesterday













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
yesterday





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
yesterday

















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