Default route and zero route

朱雀 2021-12-17 14:39 255阅读 0赞

A **default route** of a computer that is participating in [computer networking][] is the [packet][] forwarding rule (route) taking effect when no other route can be determined for a given [Internet Protocol][] (IP) destination address. All packets for destinations not established in the [routing table][] are sent via the default route. This route generally points to another router, which treats the packet the same way: If a route matches, the packet is forwarded accordingly, otherwise the packet is forwarded to the default route of that router. The process repeats until a packet is delivered to the destination. Each router traversal counts as one hop in the distance calculation for the transmission path.

The route evaluation process in each router uses the [longest prefix match][] method to obtain the most specific route. The network with the longest [subnet mask][] that matches the destination [IP address][] is the next-hop network gateway.

The default route in [Internet Protocol Version 4][] (IPv4) is designated as the zero-address [0.0.0.0][]/0 in [CIDR notation][],[\[1\]][1] often called the quad-zero route. The subnet mask is given as /0, which effectively specifies all networks, and is the shortest match possible. A route lookup that does not match any other route, falls back to this route. Similarly, in [IPv6][], the default route is specified by ::/0.

In the highest-level segment of a network, administrators generally point the default route for a given host towards the router that has a connection to a [network service provider][]. Therefore, packets with destinations outside the organization's [local area network][], typically destinations on the [Internet][] or a [wide area network][], are forwarded to the router with the connection to that provider.

The device to which the default route points is often called the [default gateway][], and it often carries out other functions such as packet filtering, [firewalling][], or [proxy server][] operations.

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If set up a vpn tunel ,

Appliance 1 > : local gateway : 172.26.0.100 ; local tunnel : 2.2.2.2/24

Appliance 2> : local gateway : 172.26.0.101 ; local tunnel :0.0.0.0/0

Then all traffic which is sent from tunnel : 2.2.2.2/24 will go into VPN tunnel.

转载于:https://www.cnblogs.com/kungfupanda/p/3191754.html

[computer networking]: http://en.wikipedia.org/wiki/Computer_networking
[packet]: http://en.wikipedia.org/wiki/Packet_%28information_technology%29
[Internet Protocol]: http://en.wikipedia.org/wiki/Internet_Protocol
[routing table]: http://en.wikipedia.org/wiki/Routing_table
[longest prefix match]: http://en.wikipedia.org/wiki/Longest_prefix_match
[subnet mask]: http://en.wikipedia.org/wiki/Subnetwork_mask
[IP address]: http://en.wikipedia.org/wiki/IP_address
[Internet Protocol Version 4]: http://en.wikipedia.org/wiki/IPv4
[0.0.0.0]: http://en.wikipedia.org/wiki/0.0.0.0
[CIDR notation]: http://en.wikipedia.org/wiki/CIDR_notation
[1]: http://en.wikipedia.org/wiki/Default_route#cite_note-1
[IPv6]: http://en.wikipedia.org/wiki/IPv6
[network service provider]: http://en.wikipedia.org/wiki/Network_service_provider
[local area network]: http://en.wikipedia.org/wiki/Local_area_network
[Internet]: http://en.wikipedia.org/wiki/Internet
[wide area network]: http://en.wikipedia.org/wiki/Wide_area_network
[default gateway]: http://en.wikipedia.org/wiki/Default_gateway
[firewalling]: http://en.wikipedia.org/wiki/Firewall_%28networking%29
[proxy server]: http://en.wikipedia.org/wiki/Proxy_server