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MPLS VPN - ROUTE TARGET IMPORT

Ratheesh mv
Beginner
Beginner

PVT.PNG

 

 

 

Situation 1:-When PE-1, PE-2 PE-4 are using same RD for the same customer VRF :-(All are having RD 1:1)
========================================================================================================
PE-4 is importing all routes(from PE-1 and PE-2) to "sh ip bgp vpnv4 vrf NEW" database from "sh ip bgp vpnv4 all"

Situation 2:-When PE-1 and PE-2 are using same RD and PE-4 is using different RD for the same customer VRF (PE1&PE2 RD 1:1 PE4 RD IS 10:10)
==========================================================================================================================================
PE-4 is importing only best bath to "sh ip bgp vpnv4 vrf NEW" database from "sh ip bgp vpnv4 all"

Why is PE-4 behaving in different way in each situation? What is the reason behind of this behavior?

OUTPUTS Situation 1:
======================

PE-4#sh ip bgp vpnv4 all
BGP table version is 10, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf NEW)
* i 5.5.5.5/32 2.2.2.2 0 100 0 65000 i
*>i 1.1.1.1 0 100 0 65000 i
PE-4#

PE-4#sh ip bgp vpnv4 vrf NEW
BGP table version is 19, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf NEW)
* i 5.5.5.5/32 2.2.2.2 0 100 0 65000 i
*>i 1.1.1.1 0 100 0 65000 i
PE-4#
PE-4#
OUTPUT Situation 2:
=====================
PE-4#sh ip bgp vpnv4 all
BGP table version is 14, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i
* i 2.2.2.2 0 100 0 65000 i
Route Distinguisher: 10:10 (default for vrf NEW)
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i

PE-4#sh ip bgp vpnv4 vrf NEW
BGP table version is 14, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 10:10 (default for vrf NEW)
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i
PE-4#

 

Thanks in advance 

11 Replies 11

mohAmed khAdr
Beginner
Beginner

Can you post z conf on P?

Also on P:  sh ip bg nei xx.xx.xx.xx adv-route and reci-rou for both PE1 &2

Thx

mohamed

PE-1#sh ip bgp vpnv4 all neighbors 4.4.4.4 advertised-routes
BGP table version is 2, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf TEST)
*> 5.5.5.5/32 192.168.15.5 0 0 65000 i

Total number of prefixes 1
PE-1#

 

PE-2#sh ip bgp vpnv4 all neighbors 4.4.4.4 ad
BGP table version is 2, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
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 valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf TEST)
*> 5.5.5.5/32 192.168.25.5 0 0 65000 i

Total number of prefixes 1

Without seeing how P is conf, try add RT on P:

under ip vrf  xxxx

route-target both 1:100

!

exit

!

then, do clear ip bg *

wait for bgp table to populate, then check again.

HTH

mohamed

 

 

MHM Cisco World
Advisor
Advisor

friend RD it not effect here RT is effect, 

use same RT in all PE and you get same if you use same or different RD. 

Giuseppe Larosa
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hello @Ratheesh mv ,

the practical result is the same as the best path is 5.5.5.5/32 via 1.1.1.1 Pe-1 for its lower BGP RID in both scenarios.

 

You should change the RD used on PE1 and PE2 to have both routes imported in VRF . This is the trick used in real world to foul the BGP route reflector servers ( to avoid propagation of best path only)

 

I you had changed the RT to a non matching value in scenario 2 you would import 0 routes.

 

Hope to help

Giuseppe

 

Giuseppe,

So, if I am doing this in real prod envo, should I have diff values for RD on both PE1& 2 or shout it be same value?

Thx

mohamed

Hello @mohAmed khAdr ,

in real world if you want the backup route to be propagated everywhere the best choice is different RD on PE-1 and PE-2.

 

So that in case of failure of primary path  PE-1 will send an update with the VPNv4 prefix in the withdrawn section and all remote PE nodes have already the backup path .

Otherwise, after PE-1 withdraw the backup path needs to be propagated from the first RRS up to all remote PE nodes and this can take some time as it happens at scheduled intervals and not on demand.

 

On the other hand you are using double memory on RRS and on each PE node.

 

Hope to help

Giuseppe

 

Thx Giuseppe, 

As usual right on point and guiding me when I need directions.

Warm Regards,

mohmaed

Hi Giuseppe Larosa, First of all thanks for your response.

 

 I have been seeing two routes one from PE-1 and another from PE-2 in the show ip bgp vpnv4 vrf xxx database in the situation 1 and situation 2. But only the best path is being imported to show ip bgp vpnv4 vrf xxxx database in the situation 2 while PE-4 is importing best and back-up route  to show ip bgp vpnv4 vrf xxxx database in the situation 1.

 

As per my understanding here route-target is perfect that is what PE-4 importing those 2 paths to show ip bgp vpnv4 vrf xxxx database in the situation 1 and situation 2. 

>Why is PE-4 importing best and backup to show ip bgp vpnv4 vrf xxxx database from show ip bgp vpnv4 vrf xxxx database in the situation 1 ?

 

>Why is not PE-4 importing best and backup to show ip bgp vpnv4 vrf xxxx database from show ip bgp vpnv4 vrf xxxx database in the situation 2 ?

 

 

PE-4#sh ip bgp vpnv4 all --------------------->Situation 2  -PE-4 having RD 10:10 for the same customer .PE-1 & PE-2 RD are 1:1
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i
* i 2.2.2.2 0 100 0 65000 i
Route Distinguisher: 10:10 (default for vrf NEW)
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i

 

PE-4#sh ip bgp vpnv4 vrf NEW----------->There are 2 path in the above output but here in the sh ip bgp vpnv4 vrf NEW database only one path.
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 10:10 (default for vrf NEW)
*>i 5.5.5.5/32 1.1.1.1 0 100 0 65000 i
PE-4#

--------------------------------------------------------------------------------------------------------------------------------------------------------------

 

 

Situation -1 

===========

PE-4#sh ip bgp vpnv4 all---------------------->In the Situation -1  & Situation -2 sh ip bgp vpnv4 all database is same .In the both case there 2  paths
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf NEW)
* i 5.5.5.5/32 2.2.2.2 0 100 0 65000 i
*>i 1.1.1.1 0 100 0 65000 i
PE-4# 

 

PE-4#sh ip bgp vpnv4 vrf NEW --->In this database also PE-4 has two paths .But in the situation 1 there was only best path .There was no back-up path. 
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf NEW)
* i 5.5.5.5/32 2.2.2.2 0 100 0 65000 i
*>i 1.1.1.1 0 100 0 65000 i

Hello @Ratheesh mv ,

I have no ready explanation for waht you see in your tests.

Changing the RD and not the RT should not influence what VPNv4 routes are imported in the VRF.

What is important is that the backup path is received from PE-4 and ready to be used if the best path fails.

 

What you see may depend on the way you do the tests , if you are using emulation software and the IOS XE images you are using.

 

From a design point of view , if you want both routes imported in vrf differentiate the RDs also on PE-1 and PE-2.

In my working experience we have made this choice having a specific per PE RD value even when using the convention

AS number (16 bit): value (32 but)

with the <value> using very big values starting from 1 and coding the customer ID and site ID and even the PE.

For other customers we used the other convention with RD values

IP address: value (16 bit)  where IP address is the PE loopback address,

 

Having an easy to recognize RD helps in troubleshooting in a big network.

 

Most basic introductions to Layer 3 VPN use the same RD on all PE nodes but this is not a real requirement. I would say that in real world you want a different RD per PE per VRF

 

Hope to help

Giuseppe

 

MHM Cisco World
Advisor
Advisor

Hello All 
same RD for same CE in two different PE:-
this make PE1 and PE2 advertise same Prefix+RD, 
the issue here is if there is RR in Path between PE1,PE2 toward PE3. 
RR will advertise only one Prefix+RD and this make other Prefix+RD always hidden from PE3.
Solution "ONLY FOR MPLS VPN" 
use different RD  this make RR advertise both Prefix+RD1 Prefix+RD2 toward PE3 and this make PE3 do :-
1- load sharing using multipath
2- Primary/Backup

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