BGP/Examples/Example 1:One router with two peers

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Revision as of 19:42, 29 May 2008 by RichardJune (Talk | contribs)
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This is meant to be an example, and not a complete BGP (Border Gateway Protocol) routing configuration.

Scenario

You have two connections to the internet. One connection through ISP 1, one connection through ISP 2. You need to advertise your network of 192.168.10.0/24 to both ISPs, and accept full feeds from both of them. The router has two ethernet interfaces, one connected to a LAN used by your servers, the other connected to a network used by your customers or employees.

Network Diagram

--------------------        -------------------------
|                  |        |                       |
| ISP 1            |        |   ISP 2               |
| AS  64513        |        |   AS  514             |
| IP  172.16.96.76 |        |   IP  10.200.10.3     |
|                  |        |                       |
--------------------        ------------------------
      |                          |
 EBGP |   +----------------------+    
      |   |      EBGP       
      |   |              
---------------------------------------------------------
      |   |     AS 64512
+--------------+               +-------------------+
| Main Router  |               | LAN               |
| 192.168.10.5 |---------------| 192.168.10.129/25 |
+--------------+  Ethernet 1   +-------------------+
      |                                 
      | Ethernet 0      
      |                
+-----------------+                      
| Servers         |
| 192.168.10.1/25 |          
+-----------------+          

Ensure that all routers running BGP have at least 256 MB of memory. Remember to save your configurations to flash whenever you are finished configuring your dynamic routing setup! To enable BGP, do the following:

  1. At the Login: prompt, enter root.
  2. At the Password: prompt, enter your password.
  3. Choose Option 1 (Configuration and Update Menu) from the Main Menu. Select Option 3 (Service Configuration).
  4. From the Service Configuration menu, you can see the status of the Dynamic routing (gated) package. If gated is running, the option will show "(running)".
  5. To start gated, choose Option 3 (Dynamic routing) and choose Option 5 (Start gated) from the Dynamic routing menu. You will also want to select Option 3 (Enable gated on boot) to ensure that BGP session will be established at boottime. Ensure that you have configured gated prior to attempting to start it. Unless it is properly configured, gated will not start.

In our example above, we will be configuring the "Main Router". From the Dynamic routing menu, choose Option 1 (gated configuration). Our AS for this example will be 9009. Choose Option 4 (Configure BGP) from the menu. This will open a file in your default editor.

  1. Edit the "autonomoussystem" parameter. In this case, our AS number is 9009:
  2. Edit the first "External peeras" section
  3. Add additional sections for each external and internal peer

The completed file for our example should look like this:

!
# This ASN is for testing and internal use *ONLY*
router bgp 64512
 bgp router-id 192.168.10.5
 bgp log-neighbor-changes
 network 192.168.10.0/24

 # Begin configuration for ISP 1
 neighbor 172.16.96.76 remote-as 64513
 neighbor 172.16.96.76 soft-reconfiguration inbound
 neighbor 172.16.96.76 description ISP 1
 neighbor 172.16.96.76 route-map rm_peer_1_in in
 neighbor 172.16.96.76 route-map rm_peer_1_out out

 # Begin configuration for ISP 2
 neighbor 10.200.10.3 remote-as 514
 neighbor 10.200.10.3 soft-reconfiguration inbound
 neighbor 10.200.10.3 description ISP 2
 neighbor 10.200.10.3 route-map rm_peer_2_in in
 neighbor 10.200.10.3 route-map rm_peer_2_out out
!
ip prefix-list pl_peer_1_out seq 5 permit 192.168.10.0/24
ip prefix-list pl_peer_2_out seq 5 permit 192.168.10.0/24
!
route-map rm_peer_1_out permit 5
 match ip address prefix-list pl_peer_1_out
 set as-path prepend 64512 
!
route-map rm_peer_1_in permit 5
 # Adjust this to favor some peers over others.
 #  Higher number is more preferred
 #  0 - 255 with 100 being the default
 set local-preference 100
!
route-map rm_peer_2_out permit 5
 match ip address prefix-list pl_peer_2_out
 set as-path prepend 64512 
!
route-map rm_peer_2_in permit 5
 # Adjust this to favor some peers over others.
 #  Higher number is more preferred
 #  0 - 255 with 100 being the default
 set local-preference 100
!

Remember to save your configurations to flash whenever you are finished configuring your dynamic routing setup!

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