BGP in contrast to different protocols doesn’t do load stability by default and installs a single finest route within the routing desk by default. Even within the BGP desk you see a single finest route.
However like different protocols in BGP we will use the ‘multipath’ command to put in a couple of route for a prefix within the routing desk.
BGP Multipath: State of affairs Instance
On this publish we’ll use the topology diagram under and perceive the configuration of BGP multipath.
Within the above publish we have now buyer working AS 100 and a service supplier working on AS 200. R1 is the CE router which is twin homed with two PE routers of the service supplier and working EBGP with them. Preserving the whole lot on the default if we wish to attain 4.4.4.4 deal with from R1 we may have solely a single finest path put in on the routing desk.
Outputs as under from R1:
BGP router identifier 1.1.1.1, native AS quantity 100
BGP desk model is 2, important routing desk model 2
1 community entries utilizing 144 bytes of reminiscence
2 path entries utilizing 160 bytes of reminiscence
1/1 BGP path/bestpath attribute entries utilizing 136 bytes of reminiscence
1 BGP AS-PATH entries utilizing 24 bytes of reminiscence
0 BGP route-map cache entries utilizing 0 bytes of reminiscence
0 BGP filter-list cache entries utilizing 0 bytes of reminiscence
BGP utilizing 464 complete bytes of reminiscence
BGP exercise 1/0 prefixes, 2/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
9.9.12.2 4 200 25 24 2 0 0 00:19:10 1
9.9.13.3 4 200 23 22 2 0 0 00:17:07 1
Within the BGP desk we see we’re getting the route for R4 from each R2 and R3 however route from R3 is taken into account as the perfect beneath routing desk as a result of BGP path choice standards.
R1#sh ip bgp | b 4.4.4.4
*> 9.9.13.3 0 200 I #####Greatest Route######
R1#sh ip route | b 4.4.4.4
B 4.4.4.4 [20/0] by way of 9.9.13.3, 00:14:16
Within the above configuration solely single hyperlink from R1 > R3 shall be used to succeed in 4.4.4.4 deal with.
Now allow us to suppose we wish to use each paths R1>R2 and R1>R3 to succeed in 4.4.4.4, so we’ll make use of BGP multipath choice to maintain each the parallel paths within the routing desk. To ensure that each the parallel paths to be put in within the BGP routing desk we’ll want to ensure the next BGP attributes are saved similar on each paths.
- Weight
- Native Desire
- AS Path (each AS quantity and AS path size)
- Origin code
- MED
- IGP metric
Multipath may be configured for 3 choices:
- iBGP Multipath: If two parallel paths exist in Ibgp.
- eBGP Multipath: If two parallel paths exist in EBGP
- eiBGP Multipath: If two parallel paths exist with a mixture of EBGP and IBGP.
In our situation we’re getting two parallel paths from EBGP, therefore we will use EBGP multipath in our configuration on R1 as under:
R1(config-router)#maximum-paths 2
Now if we verify we shall be getting each the routes put in within the routing desk of R1.
R1#sh ip bgp
Standing codes: s suppressed, d damped, h historical past, * legitimate, > finest, i – inside,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V legitimate, I invalid, N Not discovered
Community Subsequent Hop Metric LocPrf Weight Path
*m 4.4.4.4/32 9.9.12.2 0 200 I ##‘m’ means multipath enabled #
*> 9.9.13.3 0 200 i
R1#sh ip route
C 1.1.1.1 is straight related, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
B 4.4.4.4 [20/0] by way of 9.9.13.3, 00:01:36
[20/0] by way of 9.9.12.2, 00:01:36
9.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C 9.9.12.0/24 is straight related, FastEthernet0/0
L 9.9.12.1/32 is straight related, FastEthernet0/0
C 9.9.13.0/24 is straight related, FastEthernet1/0
L 9.9.13.1/32 is straight related, FastEthernet1/0
Therefore we see route for 4.4.4.4 on R1 is put in within the routing desk from each R2 and R3.
