WB1 7.26 BGP Bestpath Selection - DMZ Link Bandwidth

7.26 BGP Bestpath Selection - DMZ Link Bandwidth
• Remove the Route-ID configurated in the previous section.
• Modify the configuration of AS 100 routers so that R1 load-balances to the paths in AS 54 proportional to the bandwidth of the links connecting R4 and R6 to AS 54 routers.
 
Note
 
This feature is called DMZ Link Bandwidth in IOS. The rationale behind this name is that load-balancing is based on the bandwidth of the links connecting the border BGP peers to their neighbors. Here is how it works for a single router with multiple eBGP peering links:
 
1) You enable the feature in a border BGP router using the command
bgp dmzlink-bw
neighbor <IP> send-community extended  (iBGP peering links)
neighbor <IP> dmzlink-bw  (external BGP peers)
 
The bandwidth is computed based on the bandwidth command configured on the respective interfaces. (external BGP peers link interface)
 
2) Provided that an internal BGP speaker has both
bgp maximum-path ibgp ---> 我的路由器設定為 maximum-paths ibgp 16
bgp dmzlink-bw
 
In our scenario, we have two border BGP routers – R4 and R6 peering with the same AS 54. Our goal is to make R1 learn about the bandwidth of the links connectiong R4 and R6 to AS 54 and enable load-balancing. We achive this by configuring R4 and R6 to send extended communities to R1 and enabling dmzlink bandwidth feature in R4 and R6. At the same time, R1 is configured for iBGP multipathing, and inserts both both sets of paths into the local RIB.
 
Configuration

R4:
router bgp 100
bgp dmzlink-bw
neighbor 155.1.146.1 send-community extended
neighbor 204.12.1.254 dmzlink-bw

R6:
router bgp 100
bgp dmzlink-bw
neighbor 155.1.146.1 send-community extended
neighbor 54.1.1.254 dmzlink-bw
!
interface Serial 0/0/0
bandwidth 2000
 
R1:
router bgp 100
bgp dmzlink-bw
maximum-path ibgp 2
 
--------------------------------------------
 
Rack1R1#show ip bgp 119.0.0.0
BGP routing table entry for 119.0.0.0/8, version 169
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: iBGP
Flag: 0x8800
  Advertised to update-groups:
        1    2
  54, (Received from a RR-client)
    54.1.1.254 (metric 2560002816) from 155.1.146.6 (150.1.6.6)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath
      DMZ-Link Bw 250 kbytes
  54, (Received from a RR-client)
    204.12.1.254 (metric 2560002816) from 155.1.146.4 (150.1.4.4)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath, best
      DMZ-Link Bw 12500 kbytes
Rack1R1#

Notice the DMZ-Link Bw attribute values for both paths. Their ratio is 12500/250=50.

Rack1R1#show ip route 119.0.0.0
Routing entry for 119.0.0.0/8
  Known via "bgp 100", distance 200, metric 0
  Tag 54, type internal
  Last update from 204.12.1.254 00:02:37 ago
  Routing Descriptor Blocks:
  * 204.12.1.254, from 155.1.146.4, 00:02:37 ago
      Route metric is 0, traffic share count is 48
      AS Hops 1
      Route tag 54
    54.1.1.254, from 155.1.146.6, 00:02:37 ago
      Route metric is 0, traffic share count is 1
      AS Hops 1
      Route tag 54
Rack1R1#