It is best to add static routes to your networks 'default gateway' which is usually either a network Firewall or a router. I believe the current method if done in OS X would be to use the pf firewall to setup a rule for forwarding traffic between the two networks. However El Capitan has also made using pf a little bit more complicated. I was able to add a route across an interface by using the -link option to specify a MAC address. Route add -host 54.81.143.201 -link mac addr of 192.168.15.1 on en0 That will send traffic for 54.81.143.201 out the appropriate interface. You do have two separate 192.168.15. host addresses assigned, one to each interface, right? Else, you may send traffic out of either interface, but traffic will return on. To print the routing table on a Mac OS X computer, you must open a Terminal window. Terminal can be found by opening the Finder, selection Applications and Utilities. To open a terminal session, double-click on 'Terminal.app'. Inside the Terminal application, the route print command is 'netstat -nr'.
In the 1st part of the IP Routing series, we learned the fundamentals of Linux IP Routing.
Route command is used to show/manipulate the IP routing table. It is primarily used to setup static routes to specific host or networks via an interface.
In this article we will see how to manipulate the routing tables in Linux using route command.
We'll first explain how routing is done with some basic route command examples, and then we'll explain using a sample network architecture about how to setup routes in your network.
I. How Routing is Done?
1. Display Existing Routes
route command by default will show the details of the kernel routing table entries. In this example, the ip-address of the system where the route command is being executed is 192.168.1.157
The above command shows that if the destination is within the network range 192.168.1.0 – 192.168.1.255, then the gateway is *, which is 0.0.0.0.
When packets are sent within this IP range, then the MAC address of the destination is found through ARP Protocol and the packet will be sent to the MAC address.
If you don't know what ARP is, you should first understand how ARP protocol works.
In order to send packets to destination which is not within this ip range, the packets will be forwarded to a default gateway, which decides further routing for that packet. We will see this shortly.
By default route command displays the host name in its output. We can request it to display the numerical IP address using -n option as shown below.
2. Adding a Default Gateway
We can specify that the packets that are not within the network has to be forwarded to a Gateway address.
The following route add command will set the default gateway as 192.168.1.10.
Now the route command will display the following entries.
Now we have just added a default gateway to our machine. To verify whether it is working properly, ping some external host (for example, google.com) to send ICMP packet.
The following is the sequences of evets that happens when the above ping command is executed.
- First it will query the DNS server to obtain the ip-address of google.com ( for example: 74.125.236.34 )
- The destination address ( 74.125.236.34 ) is not within the network range.
- So, in Layer-3 (IP header) the DESTINATION IP will be set as '74.125.236.34'.
- In Layer-2, the DESTINATION MAC address will be the filled in as the MAC address of the default gateway ( 192.168.1.10's MAC ). The MAC will be found by using ARP as described earlier.
- When the packet is sent out, the network switch ( which works on Layer-2 ), send the packet to the default gateway since the destination MAC is that of the gateway.
- Once the gateway receives the packet, based on its routing table, it will forward the packets further.
The above 2 examples would have given a good idea about how routing is done within a network. Now we will see other command line options available with route command.
3. List Kernel's Routing Cache Information
Kernel maintains the routing cache information to route the packets faster. We can list the kernel's routing cache information by using the -C flag.
4. Reject Routing to a Particular Host or Network
Sometimes we may want to reject routing the packets to a particular host/network. To do that, add the following entry.
As you see below, we cannot access that particular host (i.e .51 host that we just rejected).
However we can still access other hosts in the network (for example, .52 host is still accessible).
Route Add For Mac Os
If you want to reject an entire network ( 192.168.1.1 – 192.168.1.255 ), then add the following entry.
Now, you cannot access any of the host in that network (for example: .51, .52, .53, etc.)
II. A Sample Network Architecture (to understand routing)
Let us use the following sample network architecture for the rest of the examples.
In the diagram below, we have 2 individual networks ( 192.168.1.0 and 192.168.3.0, with subnet mask of 255.255.255.0 ).
We also have a 'GATEWAY' machine with 3 network cards. 1st card is connected to 192.168.1.0, 2nd card is connected to 192.168.3.0, and the 3rd card is connected to the external world.
5. Make 192.168.3.* Accessible from 192.168.1.*
Now we need to add a routing entry such that we are able to ping 192.168.3. series ip-addresses from 192.168.1. series. The common point we have is the GATEWAY machine.
Route Add Mac Interface
So, on each machine in 192.168.1.* network a default gateway will be added as shown below.
Now when 192.168.1.1 pings 192.168.3.1, it will go to the GATEWAY via 192.168.1.10.
In GATEWAY, add the following routing entry.
Now all the packets addressed to 192.168.3.* network will be forwarded via the 192.168.3.10 interface, which then delivers the packets to the addressed machine.
6. Make 192.168.1.* Accessible from 192.168.3.*
It is very similar to what we did earlier.
So, on each machine in 192.168.3.* network a default gateway will be added as shown below.
In GATEWAY, add the following routing entry.
Now 192.168.3.* machines can ping 192.168.1.* machines.
7. Allow Internet Access ( External World )
In the previous two example, we have interconnected the 2 different networks.
Now we need to access the internet from these 2 different networks. For that, we can add a default routing ( when no routing rule matches ) to the 125.250.60.59 which is connected to the external world as follows.
This is how it works:
- Now when you try to access the internet (for example: ping google.com) from any of these machines (for example, from 192.168.3.2), the following is the sequence of events that happens.
- Since the destination (google.com) is not within 3.* series, it will be forwarded to GATEWAY via 3.10 interface
- In GATEWAY, it checks whether the destination is within 1.* range. In this example, it is not.
- It then checks whether the destination is within 2.* range. IN this example, it is not
- Finally, it takes the default route to forward the packets (i.e using the 125.250.60.59 interface, which is connected to the external world).
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Belkin Wireless Router (F5D8236-4, F6D4230-4/N150)
- Open a web browser and enter (the default IP for most Belkin routers is 192.168.2.1) and press Enter. Click Login button to open the login screen. When the login window appears, enter a password.
- Select Wireless -> MAC Address Control from the menu on the left.
- If Allow radio button is enabled proceed to the next step, otherwise, close the web browser window.
- In the MAC Address field that is blank, type in the MAC address of the wireless computer you want to be able to access the wireless network, then click Add. To find the MAC address on a computer, refer to the How to find MAC address page.
- Click Apply Changes.
D-Link Gaming Router (DGL-4500)
- Open a web browser and enter http:// (the default IP for mostD-Link routers is 192.168.0.1) and press Enter. When the login window appears, select Admin from the drop-down menu and then enter your password. Type in the graphical authentication code (if you cannot read it, click Regenerate).
- Click on Advanced and then click MAC Address Filter.
- Verify Configure MAC Filtering below setting. If it is set to Turn MAC Filtering On and ALLOW computers listed to access the network proceed to the next step, otherwise, close the web browser window.
- Enter the MAC address of your computer into the MAC address field and click Add. To find the MAC address on a computer, refer to the How to find MAC address page.
- Click Save Settings.
D-Link Router (DIR-601, DIR-615, DIR-625, DIR-628, DIR-632, DIR-655, DIR-815, DIR-825, WBR-2310)
- Open a web browser and enter http:// (the default IP for most D-Link routers is 192.168.0.1) and press Enter. When the login window appears, Select Admin from the drop-down menu and then enter your password. For WBR-2310 - enter the user name and your password.
- Click on Advanced and then click Network Filter.
- Verify Configure MAC Filtering below setting. If it is set to Turn MAC Filtering On and ALLOW computers listed to access the network proceed to the next step, otherwise, close the web browser window.
- Enter the MAC address of your computer into the first empty MAC Address field or the first MAC Address field containing all zeroes (00:00:00:00:00:00 or 00-00-00-00-00-00). To find the MAC address on a computer, refer to the How to find MAC address page.
- Click Save Settings.
