Information Technology Reference
In-Depth Information
If multiple BGP sessions are used, for example, one for each link, the practice of using BGP
to choose a single path results in only a single link's being used. If a link fails, traffic fails
over to another link, but multiple links are not used.
There are two popular options for load sharing over multiple links—EBGP multihop and
EBGP multipath. They are examined next.
EBGP Multihop Solution
The first solution is to use the eBGP multihop feature. This solution uses a single eBGP
session between the two routers, with the eBGP session being sourced from a loopback
instead of a physical interface. A static route to the remote loopback is configured for each
interface. This provides the next-hop resolution and load balancing through recursive
routing to the next hop. This scenario is shown in Figure 6-6. The router configuration and
resulting output are shown in Examples 6-2 and 6-3.
Figure 6-6
Multiple Connections Using EBGP Multihop
ISP (AS 100)
Loopback
Loopback
Enterprise (AS 65100)
Configuration on the Enterprise and Provider Routers
Example 6-2
Enterprise#show running-config | begin bgp
router bgp 65100
no synchronization
bgp log-neighbor-changes
network 172.18.0.0
neighbor 172.16.2.1 remote-as 100
neighbor 172.16.2.1 ebgp-multihop 2
neighbor 172.16.2.1 update-source Loopback0
continues
