MAC addresses are layer-2 addresses in the frame header. The layer-2 frame encapsulates the layer-3 IP packet. The layer-2 frame is stripped off at a layer-2/3 boundary (e.g. Open your Web browser and type your router’s IP address into the address bar. So, for most SMC routers, you type 192.168.2.1 in your browser’s address bar to access the router’s Web page. When the router’s logon screen appears asking for a password and, on many models, a. For adding a route to the routing table Linux as well as OS X use the route command, but be aware that even here there are differences. In OS X, to specify a route for network 10.0.0.0/24 to be routed to gateway 10.0.0.1 you use the following command. $ route -n add 10.0.0.0/24 10.0.0.1. With regard to using an IP address in a different location, there used to be a feature called 'Mobile IP' which was designed for exactly that purpose. In essence, it installled a host route in the routing table of the connected layer 3 device. View routing tables and statistics using Network Utility on Mac. You can use Network Utility to examine your computer’s network routing tables by viewing a detailed summary of packet types sent and received using common network protocols. Packet summaries are provided for TCP, UDP, IP, ICMP, IGMP, IPSEC, IP6, ICMP6, IPSEC6, and PFKEY.

IP routing is the process of sending packets from a host on one network to another host on a different remote network. This process is usually done by routers. Routers examine the destination IP address of a packet , determine the next-hop address, and forward the packet. Routers use routing tables to determine the next hop address to which the packet should be forwarded.

Consider the following example of IP routing:

Host A wants to communicate with host B, but host B is on another network. Host A is configured to send all packets destined for remote networks to router R1. Router R1 receives the packets, examines the destination IP address and forwards the packet to the outgoing interface associated with the destination network.

Default gateway

A default gateway is a router that hosts use to communicate with other hosts on remote networks. A default gateway is used when a host doesn’t have a route entry for the specific remote network and doesn’t know how to reach that network. Hosts can be configured to send all packets destined to remote networks to the default gateway, which has a route to reach that network.

The following example explains the concept of a default gateway more thoroughly.

Host A has an IP address of the router R1 configured as the default gateway address. Host A is trying to communicate with host B, a host on another, remote network. Host A looks up in its routing table to check if there is an entry for that destination network. If the entry is not found, the host sends all data to the router R1. Router R1 receives the packets and forwards them to host B.

Routing table

Each router maintains a routing table and stores it in RAM. A routing table is used by routers to determine the path to the destination network. Each routing table consists of the following entries:

• network destination and subnet mask – specifies a range of IP addresses.
• remote router – IP address of the router used to reach that network.
• outgoing interface – outgoing interface the packet should go out to reach the destination network.

Command Ip Route

There are three different methods for populating a routing table:

• directly connected subnets
• using static routing
• using dynamic routing

Each of this method will be described in the following chapters.

Consider the following example. Host A wants to communicate with host B, but host B is on another network. Host A is configured to send all packets destined for remote networks to the router. The router receives the packets, checks the routing table to see if it has an entry for the destination address. If it does, the router forwards the packet out the appropriate interface port. If the router doesn’t find the entry, it discards the packet.

We can use the show ip route command from the enabled mode to display the router’s routing table.

As you can see from the output above, this router has two directly connected routes to the subnets 10.0.0.0/8 and 192.168.0.0/24. The character C in the routing table indicates that a route is a directly connected route. So when host A sends the packet to host B, the router will look up into its routing table and find the route to the 10.0.0.0/8 network on which host B resides. The router will then use that route to route packets received from host A to host B.

When working with Linux you get used to the way Linux does things, but when you switch from Linux to Mac OS X you notice that some things are handled differently.

One of these differences I came across recently. It’s about the way you read out the routes you currently have active. I was used to the way you show them in Linux with the following command:

I like to add the “-n” parameter to not resolve the IP addresses to names. This can make the output of the routes much faster.

But when you switch over to OS X you will notice that the command “route” exists but work differently. If you open the man page of “route” on a Linux system and then on OS X you will immediately see the following difference.

Show Ip Route

The Linux man pages show you this description for the command:

But the OS X man page will only show this in the description:

The missing word “show” gives the hint that the route command will not show us the routes as we are used to from Linux. To get a similar list of active routing entries as on Linux the following command has to be executed:

The output of the netstat command on Mac OS X is very similar to the output you are used to from Linux. The option “-r” tell netstat to show the routing table and the “-n” option as with the “route” command avoids DNS resolution. The netstat command is used to show more then just the routing table and is also available on Linux. When executed on Linux it will show the same output as the route command.

Adding a route

For adding a route to the routing table Linux as well as OS X use the route command, but be aware that even here there are differences. In OS X, to specify a route for network 10.0.0.0/24 to be routed to gateway 10.0.0.1 you use the following command.

But if you are on a Linux system you will have to use the following command to do the same:

The syntax is very close to the syntax of OS X but it is not identical. In the OS X the destination and gateway parameter is defined by its position in the command line, the Linux command expects the parameters to be prefixed with “-net” and “gw”.

The man page of the related commands are usually a good source of what is different between Linux and Mac OS X.

Read more of my posts on my blog at http://blog.tinned-software.net/.

Ip Route For Mac Catalina