From: Stefan L. Dozier (doziersl@yahoo.com)
Date: Wed Oct 30 2002 - 23:15:59 GMT-3
I'm working from Parkhurst's BGP-4 Command and Configuration
Handbook, chapter 7 pages 114-117 with Figure 7-1 labbed up!
I understand the "best-path algorithm" and that by default BGP
only installs the best path in the ip routing table. I also
understand the value of the maximum-paths command in that it
allows up to six paths to the same dest to be installed in the
ip routing table.
On to the lab scenario!
Initially config'd, the bgp table and ip routing table on
RouterA displays expects results.
RouterA#sh ip bgp
BGP table version is 20, local router ID is 10.1.2.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* 172.17.1.0/24 10.1.2.2 0 0 1 i
*> 10.1.1.2 0 0 1 i
RouterA#sh ip route bgp
172.17.0.0/24 is subnetted, 1 subnets
B 172.17.1.0 [20/0] via 10.1.1.2, 00:10:00
After the "maximum-paths 2" command was added to the bgp process
on RouterA.
RouterA#sh ip bgp
BGP table version is 21, local router ID is 10.1.2.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 172.17.1.0/24 10.1.2.2 0 0 1 i
* 10.1.1.2 0 0 1 i
RouterA#sh ip route bgp
172.17.0.0/24 is subnetted, 1 subnets
B 172.17.1.0 [20/0] via 10.1.2.2, 00:01:38
[20/0] via 10.1.1.2, 00:01:38
While the ip routing table displays expected results, I can't
find any information on why when I use the maximum-paths command
it seems to break the best-path algorithm and chooses the path
with the higher router-id as indicated above! And since Parkhurst
didn't find it necessary to paste the bgp table after insertion
of the maximum-paths command under the BGP process, I'm kinda
suspicious! I am missing something here?
Stefan
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