Once the proper peer placement subnet, peer IP and other details are provided, the Service Engine will initiate peering with the router. Architecture Features Guides Support.
Select Version AKO 0. This article explains the following: eBGP multihop: BGP peers are more than one hop away and in a different autonomous system. BGP peers are not directly connected. The multihop peer must be configured with the same subnet as that of the interface network. From configuration mode, confirm your configuration by entering the show interfaces , show protocols , show policy-options , and show routing-options commands.
If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration. If you are done configuring the device, enter commit from configuration mode. Repeat these steps for all BGP sessions in the topology. Configure the interfaces to the directly connected devices, and configure a loopback interface. Configure connectivity to the other devices using static routes to the loopback interface addresses. From configuration mode, confirm your configuration by entering the show interfaces and show routing-options commands.
The neighbor statement points to the loopback interface on Device C. Make sure that Device C can ping Device E, specifying the loopback interface address as the source of the ping request. From operational mode, enter the ping From operational mode, enter the show bgp summary command. From operational mode, enter the show route advertising-protocol bgp neighbor command. The send-static routing policy is exporting the static routes from the routing table into BGP.
Help us improve your experience. Let us know what you think. Do you have time for a two-minute survey? Maybe Later. BGP Multihop Sessions. Requirements No special configuration beyond device initialization is required before you configure this example. To configure Device C: Configure the interface to the directly connected device to-D , and configure the loopback interface.
Results From configuration mode, confirm your configuration by entering the show interfaces , show protocols , show policy-options , and show routing-options commands. This represents the maximum number of hops between this router and the neighbor, which is used in the TTL field of the IP packet when establishing the peer connection. If you don't specify ebgp-multihop , the router will assume that the peers are adjacent and use a TTL value of 1. However, if you specify this keyword without an argument, the router will default to a TTL value of Note that you can cause some seriously strange routing problems by using a high TTL value with this option.
Suppose you have two ISPs, and your connection to one of them becomes unavailable. The routers could discover another path to one another, and re-establish their BGP peer relationship through the second ISP.
This would cause extremely inefficient routing. You can avoid this problem by using static host routes, directing traffic for each peer router through the correct circuit. In general, we recommend using the lowest possible value that still reaches the destination.
However, RFC describes another extremely interesting way of using this feature to improve security. The idea is that the only way that a packet can reach its destination with a TTL value of or is if the source is adjacent to the destination. If a more distant device were to attempt a BGP spoofing attack, the packets would arrive with a lower TTL value unless the attacker was also on a physically adjacent network. So this reference suggests deliberately configuring your routers to use the highest possible TTL value.
Cisco implemented this feature in IOS Version
0コメント