Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 350

BGP Multipath Operation with Link Bankwidth BGP Link Bandwidth (LB) is a way to tell BGP to load-share in an unequal or weighted fashion. LB is an optional, non-transitive Extended Community that indicates the cost of the (external) link in bytes per second. LB is similar to the MED attribute and cannot extend beyond the neighboring AS. The following network diagram depicts a scenario where a 10Gbps link connects the routers R2 and R4 and a 40Gbps link connects the routers R3 and R5: Figure 36. Sample BGP Link Bandwidth Configuration In this scenario, there is an additional 40Gbps link that is sometimes activated between the routers R2 and R5. When LB is configured on the routers R2 and R3 to communicate with their EBGP peers (routers R4 and R5 respectively), router R2 advertises path X to router R1 with LB indicating that a 10Gbps link is available for communication. Also, the router R3 advertises the path X with LB indicating that a 40Gbps link is available (converted to bytes per second). If all the required Multipath criteria is satisfied, the router R1 selects both the paths as part of the BGP route selection and installs these paths in the RIB along with the relative weights of the paths. This mechanism results in load sharing of traffic corresponding to path X across both the available paths in a 4:1 ratio. The following example shows the configuration in each router shown in Figure 1: R1# interface vlan 10 ip address 1.1.1.1/24 no shut router bgp 1 maximum-paths ibgp 2 bgp dmzlink-bw neighbor 1.1.1.2 remote-as 1 neighbor 1.1.1.2 no shutdown neighbor 1.1.1.3 remote-as 1 neighbor 1.1.1.3 no shutdown R2# interface tengigbitethernet 1/1 ip address 1.1.1.2/24 no shut interface tengigbitethernet 1/2 ip address 4.4.4.1/24 no shut interface fortyGigE 1/48 ip address 5.5.5.1/24 no shut router bgp 1 maximum-paths ebgp 2 bgp dmzlink-bw Equal Cost Multi-Path (ECMP) 350