What does routing an IP address mean?












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♦
    2 days ago
















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♦
    2 days ago














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 2 days ago









Zac67

32k22163




32k22163










asked 2 days ago









TimTim

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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♦
    2 days ago














  • 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♦
    2 days ago








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♦
2 days ago





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♦
2 days ago










1 Answer
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"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
    2 days ago













  • 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
    2 days ago











  • 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
    2 days ago











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

    – Zac67
    2 days ago











  • 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
    2 days ago











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"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
    2 days ago













  • 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
    2 days ago











  • 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
    2 days ago











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

    – Zac67
    2 days ago











  • 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
    2 days ago
















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
    2 days ago













  • 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
    2 days ago











  • 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
    2 days ago











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

    – Zac67
    2 days ago











  • 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
    2 days ago














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 2 days ago

























answered 2 days ago









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
    2 days ago













  • 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
    2 days ago











  • 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
    2 days ago











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

    – Zac67
    2 days ago











  • 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
    2 days ago



















  • 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
    2 days ago













  • 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
    2 days ago











  • 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
    2 days ago











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

    – Zac67
    2 days ago











  • 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
    2 days ago

















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
2 days ago







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
2 days ago















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
2 days ago





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
2 days ago













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
2 days ago





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
2 days ago













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

– Zac67
2 days ago





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

– Zac67
2 days ago













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
2 days ago





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
2 days ago


















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