Routing
Highlighted
Routing

Routing Table Clarification

‎02-18-2020 01:51 PM

Hi everyone!

I just want to clarify the usage of the '>' (caret?) symbol in the routing table.

I thought it was used to signify which next-hop was pushed to the forwarding-table but after some experimentation, I think I've got it wrong.

 

I created two dummy routes, one with a regular next-hop and a second with a qualified next-hop.

169.254.1.1/32 *[Static/3] 4d 18:08:29
> to 10.16.104.2 via vlan.104
[Static/5] 4d 18:17:55
> to 10.16.104.1 via vlan.104

 

Both appear in the routing table as shown above, and both have the '>' symbol.

However, only one is appearing in the forwarding-table, which is behaving as I would expect.

169.254.1.1/32 user 0 10.16.104.2 ucst 1318 3 vlan.104

 

 

So, my question is, what is the '>' symbol really used for?

 

7 REPLIES 7
Highlighted
Routing

Re: Routing Table Clarification

‎02-18-2020 02:02 PM

What you are referring to should be * asterisk. 

 

*—An asterisk indicates that the route is both the active and the last active route. An asterisk before a to line indicates the best subpath to the route.

 

https://www.juniper.net/documentation/en_US/junos/topics/reference/command-summary/show-route.html

 

> is for candicate next hops 


Mengzhe Hu
JNCIE x 3 (SP DC ENT)
Highlighted
Routing

Re: Routing Table Clarification

‎02-18-2020 03:22 PM

Thanks, but I don't think I fully understand...

 

If I configure a route with two next-hops...

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.1
set routing-options static route 169.254.1.1/32 next-hop 10.16.104.2

 

Only one of these is considered a candidate next hop? Even though they're essentially identical?

169.254.1.1/32 *[Static/5] 4d 19:48:07
to 10.16.104.1 via vlan.104
> to 10.16.104.2 via vlan.104

 

 

But if I configure one of these as a qualified next hop, so the two next hops have different preferences...

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.1
set routing-options static route 169.254.1.1/32 qualified-next-hop 10.16.104.2 preference 3

 

Both are considered candidates

169.254.1.1/32 *[Static/3] 4d 18:08:29
> to 10.16.104.2 via vlan.104
[Static/5] 4d 18:17:55
> to 10.16.104.1 via vlan.104

 

 

Why does this happen?

Highlighted
Routing

Re: Routing Table Clarification

‎02-18-2020 07:55 PM

I believe in the below case you have same preference for both the route with same next hop. Hence you see ">" only for one route.

 

 

169.254.1.1/32 *[Static/5] 4d 19:48:07
to 10.16.104.1 via vlan.104
> to 10.16.104.2 via vlan.104

 

In the below case you have different preference and hence you see ">" for both the routes.First route has preference of 3 and second one has preference of 5.

169.254.1.1/32 *[Static/3] 4d 18:08:29
> to 10.16.104.2 via vlan.104
[Static/5] 4d 18:17:55
> to 10.16.104.1 via vlan.104

 

So if you have route from the same protocol (static in this case) with same preference then you may not see ">" for all the next hops.

 

Hope this helps

 

Highlighted
Routing

Re: Routing Table Clarification

‎02-19-2020 12:46 AM

Hi Luke ,

 

Good day !

 

As per your question :

 

1> question

 

Answer :

  • ">" indication the next hop the packet will be sent to
  • " * " indicates the active route that will be pushed to the forwarding table

 

2> question

If I configure a route with two next-hops...

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.1

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.2

 

Only one of these is considered a candidate next hop? Even though they're essentially identical?

169.254.1.1/32 *[Static/5] 4d 19:48:07

to 10.16.104.1 via vlan.104.   >> 1st one

> to 10.16.104.2 via vlan.104  >> 2nd one

 

Answer :

Here when you have configured both static routes both appear in the routing table as candidates  , only 1 with " * " is used , both have default preferences hence there appear in above format where the preference is not explicitly mentioned

 

[Static/5] - in this 5 is the preference value and it is default

 

3> question

 

But if I configure one of these as a qualified next hop, so the two next hops have different preferences...

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.1

set routing-options static route 169.254.1.1/32 qualified-next-hop 10.16.104.2 preference 3

 

Both are considered candidates

169.254.1.1/32 *[Static/3] 4d 18:08:29

> to 10.16.104.2 via vlan.104  >> 1st one

[Static/5] 4d 18:17:55

> to 10.16.104.1 via vlan.104  >> 2nd one

 

Answer :

Here when you have configured the preference as 3 for 10.16.104.2

Which is lower than the default value 5

Still like in the above table both the routes appear , but the format is different as for each static next hop the preference is different

 only 1 with " * " is used , in this case the one with the lower value 3

 

 

Regards 

Sharanya

Highlighted
Routing
Solution
Accepted by topic author Luke Robertson
‎02-19-2020 07:29 PM

Re: Routing Table Clarification

‎02-19-2020 10:20 AM

Hi Luke,

 

Greetings, let me try to simplify this for you, 

 

If I configure a route with two next-hops...

set routing-options static route 169.254.1.1/32 next-hop 10.16.104.1
set routing-options static route 169.254.1.1/32 next-hop 10.16.104.2

 

Only one of these is considered a candidate next-hop? Even though they're essentially identical?

169.254.1.1/32 *[Static/5] 4d 19:48:07
to 10.16.104.1 via vlan.104
> to 10.16.104.2 via vlan.104

 

Yes, and this is expected because the primary criterion for route selection is the route preference since both routes have the same preference then the Junos OS chooses in a random fashion one of the next-hop addresses to install into the forwarding table, in other words, if you don't see the ">" on a route, it means that it is not the next-hop that is forwarding the traffic and if the primary fails it is not necessary the back up for your primary since the new next-hop will be selected through a "randomizer" again, this would make much more sense if you drop in a 3rd static route with the same default preference they are all equal and the randomized will start again for all 3 if you restart the rpd or delete all static routes and add them back at the same time.

 

Now here is when the qualified next-hop is very useful with the qualified next-hope you can overwrite the default behavior ("randomize") and specify which route will be the back up in case the primary fails by modifying the preference as you did hence you will see ">" on all candite routes. 

 

Regards,
Lil Dexx
JNCIE-ENT#863, 3X JNCIP-[SP-ENT-DC], 4X JNCIA [cloud-DevOps-Junos-Design], Champions Ingenius, SSYB

 

If this solves your problem, please mark this post as "Accepted Solution" so we can help others too \:)/

 

 

 

 

Highlighted
Routing

Re: Routing Table Clarification

‎02-19-2020 10:59 AM

If you really want to get fancy with this experiment you can make both routes active by using policy statements. By default Junos will only install one active route into the forwarding table...but what if you want to have two active paths to a desitnation over two links so that both are active. This can be done with two steps.

1. set policy-option policy-statement balance-traffic from route-filter x.x.x.x/y orlonger

    set policy-option policy-statement balance-traffic then load-balance per-packet

2. set routing-options forwarding-table export balance-traffic

 

This will install both routes into the forwarding table as active and will balance traffic per flow (as per-packet is inaccurate) and you will see traffic flowing on both links.

Regards,
Daniel
Highlighted
Routing

Re: Routing Table Clarification

‎02-19-2020 07:29 PM

Thanks, I think I finally get it now.

I still just find the qualified next-hop a bit confusing, coming from a non-Juniper background.

Feedback