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[M/MX/T] BGP speaker would not receive IBGP route within its own AS in its path

  [KB32571] Show Article Properties


Summary:

M/MX/T series router cannot receive the IBGP routes which have its own AS in its path.

Example:

(lo0:1.1.1.1/24)MX1--------------AS100—EBGP---AS200---------------MX2(16.1R5.7)-----------------------IBGP AS200---------------------MX3(13.3R8.7)--------------AS200---EBGP---AS300----------------MX4(lo0:4.4.4.4/24)

MX1 AS100
MX2, MX3 AS200
MX4 AS300

MX1 configuration:

set interfaces ge-0/0/0 unit 0 family inet address 12.1.1.1/24
set interfaces lo0 unit 0 family inet address 1.1.1.1/24
set routing-options autonomous-system 100
set protocols bgp group EBGP export lo0
set protocols bgp group EBGP neighbor 12.1.1.2 peer-as 200
set policy-options policy-statement lo0 from protocol direct
set policy-options policy-statement lo0 then accept
 

MX2 configuration:

set interfaces ge-1/2/8 unit 0 family inet address 12.1.1.2/24
set interfaces ge-1/3/0 unit 0 family inet address 23.1.1.2/24
set routing-options autonomous-system 200
set protocols bgp group EBGP import prependas
set protocols bgp group EBGP export direct
set protocols bgp group EBGP neighbor 12.1.1.1 peer-as 100
set protocols bgp group IBGP export nexthop
set protocols bgp group IBGP neighbor 23.1.1.3 peer-as 200
set policy-options policy-statement direct from protocol direct
set policy-options policy-statement direct then accept
set policy-options policy-statement nexthop from protocol bgp
set policy-options policy-statement nexthop then next-hop self
set policy-options policy-statement prependas then as-path-prepend 200
 

MX3 configuration:

set interfaces ge-1/2/0 unit 0 family inet address 34.1.1.3/24
set interfaces ge-1/2/1 unit 0 family inet address 23.1.1.3/24
set routing-options autonomous-system 200
set protocols bgp group IBGP export nexthop
set protocols bgp group IBGP neighbor 23.1.1.2 peer-as 200
set protocols bgp group EBGP import prependas
set protocols bgp group EBGP export direct
set protocols bgp group EBGP neighbor 34.1.1.4 peer-as 300
set policy-options policy-statement direct from protocol direct
set policy-options policy-statement direct then accept
set policy-options policy-statement nexthop from protocol bgp
set policy-options policy-statement nexthop then next-hop self
set policy-options policy-statement prependas then as-path-prepend 200
 

MX4 configuration:

set interfaces ge-0/0/0 unit 0 family inet address 34.1.1.4/24
set interfaces lo0 unit 0 family inet address 4.4.4.4/24
set routing-options autonomous-system 300
set protocols bgp group EBGP export lo0
set protocols bgp group EBGP neighbor 34.1.1.3 peer-as 200
set policy-options policy-statement lo0 from protocol direct
set policy-options policy-statement lo0 then accept
Symptoms:

On MX2:

MX2# run show route advertising-protocol bgp 23.1.1.3
 
inet.0: 6 destinations, 7 routes (6 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 1.1.1.0/24              Self                         100        200 100 I
 
[edit]
MX2# run show route receive-protocol bgp 23.1.1.3
 
inet.0: 6 destinations, 7 routes (6 active, 0 holddown, 0 hidden)
 

On MX3:

MX3# run show route advertising-protocol bgp 23.1.1.2
 
inet.0: 6 destinations, 7 routes (6 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 4.4.4.0/24              Self                         100        200 300 I
 
[edit]
lab# run show route receive-protocol bgp 23.1.1.2
 
inet.0: 6 destinations, 7 routes (6 active, 0 holddown, 0 hidden)
Cause:

This behavior is expected.

Solution:

You can change prepending from its own number to any other.

Example:

On MX2:

set policy-options policy-statement prependas then as-path-prepend 100

On MX3:

 set policy-options policy-statement prependas then as-path-prepend 10000
 

MX2# run show route advertising-protocol bgp 23.1.1.3 

inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 1.1.1.0/24              Self                         100        100 100 I
 
MX2# run show route receive-protocol bgp 23.1.1.3 extensive
 
inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
* 4.4.4.0/24 (1 entry, 1 announced)
     Accepted
     Nexthop: 23.1.1.3
     Localpref: 100
     AS path: 10000 300 I
 

MX3# run show route advertising-protocol bgp 23.1.1.2

inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 4.4.4.0/24              Self                         100        10000 300 I
 
MX3# run show route receive-protocol bgp 23.1.1.2 extensive       
 
inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
* 1.1.1.0/24 (1 entry, 1 announced)
     Accepted
     Nexthop: 23.1.1.2
     Localpref: 100
     AS path: 100 100 I

Now, the router can receive the IBGP route.

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