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L3 MPLS/VPN use Parallel Paths for loadsharing

i have a small lab setup with two PE-routers, two P-routers and a route-reflector. see exhibit

on both pe-roouters directly connected networks in vrf RED, which is redistributed to mBGP/vrf RED

PE1 and PE5 are route-reflector clients to RR

from IGP/OSPF prespective, i have two parallel paths from PE1(loopback 192.168.4.1) to PE5 (loopback 192.168.4.5) and vice versa.

(PE1 <-> P1 <-> PE5 and PE1 <-> P2 <-> PE5)

Both networks from VPN RED use RT 65000:12

RD is 192.168.4.1:12 on PE1 and 192.168.4.4:12 on PE5

with sh ip route vrf RED i see only 1 path to the LAN's (192.168.12.0/22 and 192.168.51.0/24)

this is because PE's are using only one RD for the connected RED networks.

Is there a way to make use of parallel paths in this scenario ?

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Accepted Solutions
Cisco Employee

L3 MPLS/VPN use Parallel Paths for loadsharing

Hi,

You only have one BGP path but this path has a recursive next hop (PE loopback address) and packets to this recursive next hop will be load balanced over the multiple IGP paths. You should be able to see that by doing a "show ip cef vrf RED internal". The load balancing will be per flow. You can use "show ip cef vrf RED exact-route " to find out which IGP paths will be used by a given flow.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
3 REPLIES
Cisco Employee

L3 MPLS/VPN use Parallel Paths for loadsharing

Hi,

You only have one BGP path but this path has a recursive next hop (PE loopback address) and packets to this recursive next hop will be load balanced over the multiple IGP paths. You should be able to see that by doing a "show ip cef vrf RED internal". The load balancing will be per flow. You can use "show ip cef vrf RED exact-route " to find out which IGP paths will be used by a given flow.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: L3 MPLS/VPN use Parallel Paths for loadsharing

Hi

you are absolutely right !

r1# show ip cef vrf RED exact-route 192.168.12.3 192.168.51.1

192.168.12.3 -> 192.168.51.1 => label 35 label 24 TAG adj out of Serial0/0/0

r1# show ip cef vrf RED exact-route 192.168.12.1 192.168.51.2

192.168.12.1 -> 192.168.51.2 => label 35 label 25 TAG adj out of FastEthernet0/1, addr 10.10.10.5

btw: do you know why no next-hop ip-addr is shown on Serial while on FastEthernet it shows 10.10.10.5 ?

Both links are configured as /30 and ospf point-to-point.

thanks and regards

Cisco Employee

L3 MPLS/VPN use Parallel Paths for loadsharing

Hi,

>btw: do you know why no next-hop ip-addr is shown on Serial while on FastEthernet it shows 10.10.10.5 ?

>Both links are configured as /30 and ospf point-to-point.

The reason is that there may be several adjacencies on a broadcast interface (FE0/1), therefore you need the IP address of the next hop to make sure you use the proper one. This is not required on a point to point interface (SE0/0/0).

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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