Routing

Hi,

   This is a simple advertisement of an aggregate route between two routers. Router3 is advertising the aggregate via BGP to Router2. I see that Router2 is receiving the route from Router3 but it's hidden it. When I check why it states that it's "looped". However, I don't see how that can be looped if the AS that Router3 is using is 3333 and the AS the Router2 is using is 2222. Can you guys please check what mistake you see? Just to be clear Router1 and Router2 are not two physical devices they are both routing instances within a single device. Thank you

Router2 Output:

root# ...ve-protocol bgp 10.1.23.2 table Router2.inet.0 hidden

Router2.inet.0: 5 destinations, 5 routes (4 active, 0 holddown, 1 hidden)
Prefix Nexthop MED Lclpref AS path
200.0.100.0/22 10.1.23.2 3333 I

root# run show route protocol bgp table Router2.inet.0 hidden extensive

Router2.inet.0: 5 destinations, 5 routes (4 active, 0 holddown, 1 hidden)
200.0.100.0/22 (1 entry, 0 announced)
BGP
Next hop type: Router
Address: 0x15c0944
Next-hop reference count: 1
Source: 10.1.23.2
Next hop: 10.1.23.2 via lt-0/0/0.6, selected
State: <Hidden Ext>
Peer AS: 3333
Age: 37:00
Task: BGP_3333_2222.10.1.23.2+179
AS path: 3333 I (Looped: 3333) Aggregator: 3333 200.0.102.1
Router ID: 200.0.102.1

[edit]
root#

Router3 Output:

root# show routing-instances Router3
routing-options {
aggregate {
route 200.0.100.0/22;
}
}
protocols {
bgp {
group ROUTER2 {
type external;
description "Advertise Router3 Loopbacks to Router2";
export ADV_AGR;
peer-as 2222;
local-as 3333;
neighbor 10.1.23.1;
}
}
}

[edit]
root#

root# run show interfaces terse routing-instance Router3
Interface Admin Link Proto Local Remote
lt-0/0/0.3 up up inet 10.1.13.2/30
lt-0/0/0.7 up up inet 10.1.23.2/30
lo0.102 up up inet 200.0.102.1/24
200.0.103.1/24

[edit]
root#

root# show policy-options
policy-statement ADV_AGR {
from protocol aggregate;
then accept;
}

[edit]

Hi there,

I see You are using routing instances, and most likely on the same physical router, and not separate physical boxes, is that correct?

if yes, then please:

1/ change Your misleading diagram, and

2/ use either "as-loops" command, or "independent-domain"

The root cause is that JUNOS checks for AS path loops _across_ ALL_AS_numbers configured on the box, be it inside VR/VRF/LS or in global instance.

HTH

Thanks
Alex

Hi Alex,

  Sorry for the misleading diagram. Regarding the loop I was expericing this is only happens when one running routing instances within a single device since all routing instances belong to a single primary routing instance domain is that correct? Thank you

Victor

Hello,

If Your BGP peers are one inside VR and another in inet.0, and they use different AS numbers, then when announcing routes to each other both of them will detect a loop due to AS path check for own ASN being performed across _ALL_ ASN_ configured on local box.

Consider using iBGP, "loops" or "independent-domain" to overcome this scenario.

Thanks

Alex

Okay got it. Thank you