The AS_PATH Attribute

AS_PATH is a list of AS-numbers that the BGP route passed. Router will elect the shortest AS_PATH as the best path when other attributes are the same.

If using private AS-numbers (64512-65534), user can remove the private AS-number from the AS_PATH to prevent the leakage of private AS numbers into the Internet.

Figure 1-16

Step 1: Switch A and Switch B Enable EBGP. Switch B and Switch C Enable EBGP. Switch A uses a private AS-number 65534

Switch A:

admin@XorPlus# set protocols bgp bgp-id 33.33.33.33
admin@XorPlus# et protocols bgp local-as 10
admin@XorPlus# set protocols bgp peer 5005::1 local-ip "5005::2"
admin@XorPlus# set protocols bgp peer 5005::1 as 65534
admin@XorPlus# set protocols bgp peer 5005::1 ipv6-unicast true

Switch B:

admin@XorPlus# set protocols bgp bgp-id 9.9.9.9
admin@XorPlus# set protocols bgp local-as "65534"
admin@XorPlus# set protocols bgp peer 5005::2 local-ip "5005::1"
admin@XorPlus# set protocols bgp peer 5005::2 as "10"
admin@XorPlus# set protocols bgp peer 5005::2 ipv6-unicast true
admin@XorPlus# set protocols bgp peer 3003::1 local-ip "3003::2"
admin@XorPlus# set protocols bgp peer 3003::1 as "6"
admin@XorPlus# set protocols bgp peer 3003::1 ipv6-unicast true

Switch C:

admin@XorPlus# set protocols bgp bgp-id 6.6.6.6
admin@XorPlus# set protocols bgp local-as "6"
admin@XorPlus# set protocols bgp peer 3003::2 local-ip "3003::1"
admin@XorPlus# set protocols bgp peer 3003::2 as "65534"
admin@XorPlus# set protocols bgp peer 3003::2 ipv6-unicast true

Step 2: Check BGP peer status on Switch B

Switch B:

admin@XorPlus# run show bgp peers detail 3003::1
Peer 1: local 3003::2/50985 remote 3003::1/179
  Peer ID: 6.6.6.6
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 6
  Updates Received: 0,  Updates Sent: 1
  Messages Received: 4,  Messages Sent: 5
  Time since last received update: n/a
  Number of transitions to ESTABLISHED: 8
  Time since last entering ESTABLISHED state: 69 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds
admin@XorPlus# run show bgp peers detail 5005::2
Peer 1: local 5005::1/36229 remote 5005::2/179
  Peer ID: 33.33.33.33
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 10
  Updates Received: 1,  Updates Sent: 0
  Messages Received: 9,  Messages Sent: 8
  Time since last received update: 156 seconds
  Number of transitions to ESTABLISHED: 3
  Time since last entering ESTABLISHED state: 156 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds

Step 3: Switch A propagate a BGP route entry 7777::/64

Note :The AS-path should be 65534 on Switch B, and the AS-path should be 9 65534 on Switch C.

Switch B:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete

   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 7777::/64                     5005::2                   33.33.33.33      10 i

Switch C:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete

   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 7777::/64                     3003::2                   9.9.9.9          65534 10 i

Step 4: Remove private AS-number from AS_PATH

Note: The private AS-number should be removed from the AS-path after enabled public-as-only. It only removes the private AS-number when the private AS-number is its own.

Switch B:

admin@XorPlus# set protocols bgp peer 3003::1 public-as-only true
admin@XorPlus# commit
Merging the configuration.
Commit OK.
Save done.
admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete

   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 7777::/64                     5005::2                   33.33.33.33      10 i
admin@XorPlus#

Switch C:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete

   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 7777::/64                     3003::2                   9.9.9.9          10 i
admin@XorPlus#