Routing

Hi community,

I'm trying to figure out

1. what cannot be accomplished with forwarding type RI that can be accomplished with virtual-router type RI?

2. As far as i understand, forwarding RI can also have interfaces assigned to it.

Does this mean that these intefaces disappear from master RI and also cannot belong to any other RI?

3. What actually changes if I attach an interface to the forwarding RI?

Does this mean that all traffic entering this interface will automatically belong to this RI and be routed according to its routing table?

4. Can a virtual-router type RI send packets out of an interface that actually is not assigned to the RI (say routes are imported using rib-groups)?

Thanks for you answers.

Hi there,

My answers:

---

@raman.shcharbakou wrote:

 

 

1. what cannot be accomplished with forwarding type RI that can be accomplished with virtual-router type RI?

 

 

---

None of dynamic routing protocols work in forwarding RI. 

virtual-router RI supports all dynamic routing protocols + LDP, no RSVP support in VR.

Locally-generated OAM packets like ping cannot be forced to pass forwarding RI table lookup.

---

@raman.shcharbakou wrote:

 

 

2. As far as i understand, forwarding RI can also have interfaces assigned to it.

Does this mean that these intefaces disappear from master RI and also cannot belong to any other RI?

 

 

---

Correct.

---

 

3. What actually changes if I attach an interface to the forwarding RI?

Does this mean that all traffic entering this interface will automatically belong to this RI and be routed according to its routing table?

 

 

---

Such config does not commit.

---

 

4. Can a virtual-router type RI send packets out of an interface that actually is not assigned to the RI (say routes are imported using rib-groups)?

 

 

---

Yes it can in a general sense, but I discourage You to think of VR or any other RI as some type of walled "container" within physical router. RI is just a separate routing+forwarding table combo, sometimes just a routing table without associated forwarding table. Any packet originated on a router is build by RE CPU (sometimes by FPC CPU) and then is looked up in associated forwarding table. Similarly, a transit packet is also looked up in a forwarding table. Therefore, it's operator's job to make sure the lookup succeeds if the goal is to send pkts out of interface not belonging to a given VR and there are 2 commony used tools for that: rib-groups and "instance-import" policies.

HTH

Thanks

Alex

Thanks Alex,

This is what I was looking for.

You answeed question 3correctly that config commit will fail,

i believe you just misread question 2 where I asked about interface in a forwarding RI.

Hi there,

---

@raman.shcharbakou wrote:

Thanks Alex,

This is what I was looking for.

 

You answeed question 3correctly that config commit will fail,

i believe you just misread question 2 where I asked about interface in a forwarding RI.

---

Thanks very much for spotting the mistake, the corrected answer #2 is below

    raman.shcharbakou wrote:
   
__________________________________________________________     

    2. As far as i understand, forwarding RI can also have interfaces assigned to it.

    Does this mean that these intefaces disappear from master RI and also cannot belong to any other RI?

___________________________________________________________     

     
Your understanding is incorrect. VR can have interfaces assigned to it which disappear from global table, but forwarding RI cannot, such config does not commit.

HTH

Regards

Alex

Slight correction, raman.shcharbakou is correct, the forwarding type routing instance does not allow for adding interfaces.

HI All

I think I missed this discussion... So can anyone please repeat for an idiot, why

"forwarding" instances are at all needed, if everything can be accomplished 

by a virtual-router with no interfaces? Any example when forwarding instance

works and virtual-router doesn't?

Pk,

It is possible that you can achieve similar objectives as you are aware Juniper provides multiple ways to accomplish an objective-you chose one. For example configuring interfaces - use individual, interface-range with members only or member range etc. you can add vlan to interface at the interface...ethernet-switching vlan members or simply add interface uner vlans, or using instance-import or rib-groups. Similarly with routing instances, they are specifically designed to be used in specific situations. Simply because you can accomplish the same with vr-type as with f-type would not necessarily mean that f-type is useless and should be eliminated. I could use an 18-wheeler trailor to transport my friend from Dallas to Houston or I could use a far more efficient Hyabusa to get the same job done. Now if my friend needed to carry his/her two bedrooms and living room, that could not be accomplished with the Hyabusa but certainly with the 18-wheeler. Does the fact that the 18-wheeler can accomplish both eliminate the need for the Hyabusa? Main difference in this case with forwarding type is that you cannot add interfaces to that instance type so there is no one-one mapping of interfaces. With a virtual-router type, there is a one to one mapping of interface. F-type RI is better suited for filter based forwarding. So if you want to be able to separate routing tables for several different customers but say use the same egress interface, then a forwarding instance type would be more suitable. This could not be acomplished with virtual-router type if you place your egress interface in a virtual-router type routing instance. A forwarding instance-type could not be used for L2/L3 VPN routing.

By looking at the actual definitiosn, that may explain better that what I tried:)

http://www.juniper.net/techpubs/en_US/junos13.3/topics/concept/routing-instances-overview.html

One question- if you wanted to create multiple instances of OSPF, BGP, could that be accomplished with an F-type RI?

Hi Lyndidon,

I agree with what you say. But I'm still not sure if there is an application
of forwarding instance that can't be achieved with vr. Note that documentation
doesn't say f-instance is just a vr-lite. If they did, I would be reliefed.
But they say "Forwarding—Use this routing instance type for filter-based
forwarding applications", while I know I can use a VR as well (with or without
interfaces, btw).

On your question: you can't run BGP or OSPF because you can't have interfaces
in F-instance. But you can copy dynamic routes to it. They have a good
example with BGP in Junos Security book (end of Chapter 11).

Hi Petr,

Absense of interfaces in forwarding RI makes them unidirectional, i.e. only client->server traffic can pass forwarding RI whereas server->client passes inet.0, and both use same interface.

This makes forwarding RI useful for certain applications at no extra cost of creating rib-groups/instance-import to leak return routes.

HTTP header enrichment and WAN acceleration (now EOLed) come to mind as quick examples.

HTH

Thanks

Alex

Slightly off the topic .. RSVP under VR will be supported from 15.1 onwards ..

In short, forwarding-instance is a quick simple way to do FBF without the need for rib-groups 😉 interface-routes... 

No. If using instance-toye forwarding, you muat use rib-groups, instance-import to import information into the routing table, so that next-hos can be resolved.

Who can explain about Layer 2 VPN routing instance? I can make layer 2 circuit under protocols->l2circuit configuration. Why and where do I need to use L2 routing instance?

Hello,

You will need RI of type l2vpn when using Kompella L2VPN - it is BGP-based as opposed to L2circuits which are LDP-based

http://www.juniper.net/techpubs/en_US/junos13.2/information-products/pathway-pages/config-guide-vpns/config-guide-vpns-layer-2.html

HTH

Thanks
Alex