10-23-2007 02:37 AM - edited 03-03-2019 07:17 PM
Hi all,
If a router receives an eBGP route from two of its iBGP peers (with similar weight/local pref/metric/as path)
Is it possible for the router to put both next hop routers in the routing table or can only one "BEST" route be chosen between the two?
Note: Both paths do show up in "show ip bgp"
Looking forward to comments. Thanks in advance.
10-23-2007 02:47 AM
HI,
In my understading, BGP will select the "BEST" path to the destination.
In the above scenario, if 2" paths with similar weight/local pref/metric/as path received means,
the PATH which is FIRST injected in the routing table will be used.
PLS RATE if HELPS
Best Regards,
Guru Prasad R
10-23-2007 02:56 AM
Hi,
Upon further reading (http://www.cisco.com/warp/public/459/25.shtml), it seems that indeed a BEST path will be selected and that is the path that will be advertised to neighbours.
However, there is still the issue of BGP multipath. I don't seem to be able to get it working. maximum-paths has already been set to 2.
10-23-2007 04:13 AM
There will ALWAYS be only one best path, even in case of path load balancing.
To find out if a route is balanced or not, type "show ip bgp n.n.n.n" where n.n.n.n is a destination network.
Example:
BGP routing table entry for 100:1:10.22.22.0/24, version 50
Paths:(6 available, best #1)
Multipath:iBGP
Advertised to non peer-group peers:
200.1.12.12
22
10.22.7.8 (metric 11) from 10.11.3.4 (100.0.0.8)
Origin IGP, metric 0, localpref 100, valid, internal, multipath, best
Extended Community:RT:100:1
Originator:100.0.0.8, Cluster list:100.1.1.44
In this example with MPLS the multipath keyword denotes that this path is used with another path to propagate data.
Hope this helps.
10-23-2007 04:31 AM
HI, [PLS RATE if HELPS]
Issue #show ip route command
You can see 2" paths learned and by default load balancing should occur per-packet basis and neverthless issue #ip route-cache command over the interfaces connected to ISP to do load balancing via per-destination basis.
Hope the below explanation will fix your problem:
By default BGP chooses one best path among the possible equal-cost paths. However you can change the maximum number of parallel equal-cost paths allowed.
To make this change include:#maximum-paths paths command under the BGP Config.
User the number between 1 to 6 for the paths.
Sample Config:
!
router bgp
neighbor
neighbor
network
maximum-paths 2
!
!!This Command allows max number of paths to particular destination to install in the routing table.
Use: #show ip route and #show ip bgp
for verification.
Hope i am Informative.
PLS RATE if HELPS
Best Regards,
Guru Prasad R
10-23-2007 08:09 AM
Hi,
In addition to below said feedback, in case everything is equal like local pref, Weight,etc. then it will always consider lower router-id as best path to exit that router for outbound traffic.
10-23-2007 06:07 PM
Hi all, thanks for the comments. You are all right.
Problem is identified, silly me, I used command "maximum-paths 2" instead of "maximum-paths ibgp 2".
10-23-2007 06:13 PM
--edit--double-post--
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