Routing

Hej

I am running this on MX104 version Junos: 17.4R2.4 in a Logical System

I have configured a default aggragate route, but it is appearing as hidden. 

I am running IS-IS, IBGP and EBGP, so there should be contributing routes (non direct/local) to 0/0 for it to appear in the RT.

When I check hidden route for 0/0 exact I get a very long AS path.

odj@test3pe1dk:Oscar-Lab-R1# show routing-options aggregate
route 0.0.0.0/0;

odj@test3pe1dk:Oscar-Lab-R1# run show route 0/0 exact hidden extensive

inet.0: 873 destinations, 2126 routes (872 active, 0 holddown, 1 hidden)
0.0.0.0/0 (1 entry, 0 announced)
Aggregate
Next hop type: Reject, Next hop index: 0
Address: 0x36b3664
Next-hop reference count: 1
State: <Hidden Int Ext Changed>
Local AS: 54591
Age: 12:32:33
Validation State: unverified
Task: Aggregate
AS path: {105 221 230 235 414 522 783 794 922 1026 1158 1513 1540 1620 1701 1900 2249 2455 2621 2724 2732 2872 2911 2972 3073 3079 3093 3127 3357 3745 3780 4065 4098 4126 4199 4341 4364 4439 4473 4628 4637 4819 4832 4886 5062 5369 5376 5510 5572 5577 5646 5697 5705 6147 6221 6385 6452 6621 6695 6736 6738 6749 7318 7478 7661.............Just Goes on like this.

Thanks in advance and Regards
Oscar

Just an update. 
I have a more specific aggragate configured 172.30/18 and that does appear in the routing-table and it is not hidden

Hi Oscar,

Usually the "show route 0/0 exact hidden extensive" command itself shows the "Hidden reason" in the end.

So can you share the entire output of this command ?

Please share both outputs:

show route 0/0 exact hidden extensive

show route 0/0 exact hidden detail

Hi Oscar,

by default the aggregate will include all AS numbers from all of the contributing paths which as you can see in your output results in very long AS path which is the trigger for the route being hidden.

As per https://www.juniper.net/documentation/en_US/junos/topics/concept/policy-aggregate-routes.html

the route will be hidden when the AS path of an aggregate route—built from contributing routes— is more than half of the maximum BGP packet size (4096 bytes). Such AS paths have the OverflowASPathSize flag set for them - which is what you will likely see at the end of the AS path list in the hidden extensive output as in the example below

root@R1# run show route 0 hidden extensive

AS path: {222 330 <snip> 64345 64382} ? (LocalAgg OverflowASPathSize)

You can overcome this by changing the default behavior using this command "set routing-options aggregate defaults brief", applying it only to the default route "set routing-options aggregate route 0/0 brief" or configuring static AS path to the route.

i.e.

root@R1# set routing-options aggregate route 0.0.0.0/0 as-path path 111

root@R1# run show route 0 extensive |match "path|pref"
*Aggregate Preference: 130
AS path: 111 I

or 

root@R1# set routing-options aggregate route 0.0.0.0/0 brief

root@R1# run show route 0 extensive

*Aggregate Preference: 130
Next hop type: Reject
Address: 0x9292a44
Next-hop reference count: 3
State: <Active Int Ext>
Local AS: 111
Age: 39:47
Validation State: unverified
Task: Aggregate
AS path: ? (LocalAgg Atomic)
Flags: Brief Depth: 0 Active
AS path list:
AS path: 222 330 601 82 198 26 I (Originator)
AS path: 222 I (Originator)

Cheers,

Radek

@Radek

Hej Radek

Adding the "Brief" to the command put the default in the RT. 

Thank you for the detailed explanation of the cause. That is an interesting bit of information there.

Regards
Oscar