Labs

H,i, 

I'm currently studdying for my next Juniper certification exam and as for business need around ASPATH override feature and similar function.  I know my design do not respect BGP best practice at some point, my only gold was to experiment AS-OVERRIDE feature with Juniper v-lab .

So to understand AS override I used Juniper V-LAB "Multi-AS with Dual Route Reflectors" topologie esased all router and replace their configuration with the one attached.  At the beginning of my lab all BGP session were established and routeur are exchange as expected.

So to experiment AS-override feature I added the following 

on lo0 I added multiple secondary ip on each router VMX4, VM5 & VMX6

VMX4 10.1.101.1/24 10.1.102.1/24..... UP TO 10.1.105.1/24

VMX5 10.15.101.1/24 10.16.102.1/24..... UP TO 10.16.105.1/24

VMX6 10.16.101.1/24 10.16.102.1/24..... UP TO 10.16.105.1/24

After alterated export policy to respective ASN router were exchanged everywhere as expected.  

After that I change the ASN of VMX4 from ASN 64501 to 64515 same as for VMX5, change the respect export policy to ASN64512  on VMX4 and commit the change.  I also update peering configuration of VMX3 & VMX1 for peering configuration with vmx4 and also commit the change.

As expected, routes from VMX4 now appear in all router part of ASN64515 except on VMX5 since BGP path prenvention mecanism was prevent the advertisement of these route form VMX2 and VMX6 to VMX5.

On VMX2 I wasn't seen even route been advertised from router VMX2 to VMX5 which this behavior is different from other vendor like who in case vmx2 would be advertising these route to vmx5 and let vmx5 to not accepting theses routes due of BGP path loop prevention function.

After I add the command "advertise-peer-as" in the group to VMX5 and commit the configuration 

I seen the route from VMX4 been advertived to VMX5 but on VMX5 I did not seen them as received but not been put in the routing table due of BGP loop prevention.

This time the network from VMX4 are advertised as expected to VMX5 due to the "advertise-peer-as as-overrive" command and looks beeing originated in ASN 64516 as expected. 

on the VMX5 the receive route command getting the following result as I expect

BGP path routes was looking from loop 64516 to 64512 and back to 64516.  it was expected as I use this time "as-override" in combination with "advertise-peer-as".

Sourcing ping request from 10.12.15.1 on VMX 5 to 10.1.101.1 was successful

Sourcing ping request from 10.15.101.1 on VMX 5 to 10.1.101.1 was not successful

Sourcing ping request from 10.16.15.1 on VMX 5 to 10.1.101.1 was not successful

using traceroute I discovered the route taken when traffic was comming from 10.12.15.1 was taking aspath 64515 to 64512 and end to VMX4.  With the  2 others case, path taken was to VMX6 asn64512 and back to vmx6 but never going to VMX4.I don't know here...

So at the end my 2 questions are :

1- Why routes aren't seen as receiving routes from VMX2 when they are really advertised from VMX2 to VMX5 ?

2- Why the path taken from the loop interface aren't successful and pinng  sourcing from 10.12.15.1 are successful ?

Zip file is containing the current diagram in PDF visio format and router configuration at the beginning of the lab.

Zip file "end of the lab.zip" is containing  the router configuration at the end of the my lab configuration.  So if you want to reimport  it in Juniper V-LAB you will seeing the exact same behavior that I'm trying to explain here.  

Thank you

Attachment(s)

RR.zip   125 KB 1 version

end of the lab.zip   8 KB 1 version