maximum-paths command help require in BGP

[Dhiraj Jagdale]

Hii...

I am using cisco WS-C3750X-48P switch in branch with two different ISP's link connected and apply below config. i want to load balance the outgoing traffic with two ISP's. i have configured  " maximum-paths 2" command under BGP.

router bgp 65005
 bgp log-neighbor-changes
 neighbor 10.75.112.77 remote-as 4755
 neighbor 192.168.179.69 remote-as 9583
 maximum-paths 2
 maximum-paths ibgp  2
 !
 address-family ipv4
  neighbor 10.75.112.77 activate
  neighbor 10.75.112.77 prefix-list to-ISP out
  neighbor 192.168.179.69 activate
  neighbor 192.168.179.69 prefix-list to-ISP out
  maximum-paths 2
  maximum-paths ibgp  2
  no auto-summary
  no synchronization
  network 10.32.60.0 mask 255.255.255.0
  network 10.32.138.0 mask 255.255.255.0
  network 10.45.24.0 mask 255.255.255.192
  network 10.46.185.42 mask 255.255.255.255
 exit-address-family

In BGP table we receive two paths for each destination mention in below

Switch#sh ip bgp 10.34.14.0
BGP routing table entry for 10.34.14.0/24, version 187
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Multipath: eBGP iBGP
  Not advertised to any peer
  9583 65505
    192.168.179.69 from 192.168.179.69 (1.7.0.131)
      Origin IGP, localpref 100, valid, external, best
  4755 65088
    10.75.112.77 from 10.75.112.77 (192.168.197.46)
      Origin IGP, localpref 100, valid, external
Switch#

But in routing table still showing single best path. need both the routes in RIB for load balancing. pls help 

Switch# sh ip route 10.34.14.0
Routing entry for 10.34.14.0/24
  Known via "bgp 65005", distance 20, metric 0
  Tag 9583, type external
  Last update from 192.168.179.69 13:36:23 ago
  Routing Descriptor Blocks:
  * 192.168.179.69, from 192.168.179.69, 13:36:23 ago
      Route metric is 0, traffic share count is 1
      AS Hops 2
      Route tag 9583

Switch#

[e.ciollaro]

Is the IGP metric to the BGP neighbors the same ?

enrico.

PS: useful link: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

[Joseph W. Doherty · Accepted solution]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Maximum paths 2 is only part of what you need.  You also need to use the secret/hidden command: bgp bestpath as-path multipath-relax

[Dhiraj Jagdale]

Hi Joseph, I worked on this since last few months and didn't get success, you always helped me out for my critical issues.... and this time also..... Thanks a ton for this...i executed the command & it's working fine. both the links are utilize now. but again as usual i have questions.

1) If i am not wrong this is session wise load sharing and not per packet load balancing

2) Is there any reason Cisco keep this command hidden/secret .

Again thanks you very much for sharing this command........

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

# 1

Yes, its flow load balancing, not per packet load balancing.  The latter, as a general rule, should be avoided.

# 2

I don't know.  Something only Cisco could answer.

[e.ciollaro]

Hi Joseph

obviously we can't know  why Cisco decided to keep this command secret but might it be because this algorithm violated BGP rules that state that BGP must select a single path ? Or, in any case, is it correct that this command violate BGP specification ?

Second consideration:  using this config load-balancing is assured just in outbuond direction, isnt' it ?

Bye,

enrico