Understanding Fabric Connect Scaling

[Anonymous]

Hello community,

I would like to check if my understanding of Fabric Connect Scaling is correct.

Am I right with the following statements from the datasheets?

Fabric Connect Scaling
- Fabric Adjacencies per switch: Maximum number of directly connected fabric nodes
- BEB Nodes per VSN (I-SID): Maximum number of fabric nodes within a VSN
- L2 VSNs: Maximum number of L2 VSNs on the node
- L3 VSNs: Maximum number of L3 VSNs on the node

Furthermore, is it correct that the values of the smallest fabric node count?

1. Assuming there are only fabric nodes with 2000 BEB nodes per VSN and then a fabric node with a maximum of 500 BEB nodes per VSN is added. Then there can only be 500 nodes in this VSN, right?

2. If there is a fabric with nodes that can have 4000 L2 VSNs and a fabric node with a maximum of 512 L2 VSNs is added. Does this affect the other nodes which can have a maximum of 4000 L2 VSNs? Does this also fundamentally reduce them to 512 L2-VSNs or only to the specific L2-VSN as in point 1.?

Many thanks and best regards
Jan

[Roger_Lapuh]

Hi Jan

let me provide you some answers to your questions:

Fabric Connect Scaling

Q: - Fabric Adjacencies per switch: Maximum number of directly connected fabric nodes

A: This includes direct NNIs but also logical NNIs (Fabric Extend or SD-WAN).

Q: - BEB Nodes per VSN (I-SID): Maximum number of fabric nodes within a VSN

A:  This refers to the maximum number of fabric switches in the same IS-IS area. If you want to span an ISID beyond this value you will need to build a multi-area IS-IS fabric network. 2 Area boundary nodes count as 3 fabric nodes as they form a virtual area node representing the network "behind" them.

Keep in mind this published number is the maximum best case number. The switches provide (Rel 9.1 KHI) information about their scaling situation.

Q: - L2 VSNs: Maximum number of L2 VSNs on the node

A:  Yes, this refers to the number of supported L2 services (L2 ISIDs) that can be terminated on this device.

Q: - L3 VSNs: Maximum number of L3 VSNs on the node

A:  Yes, this refers to the number of supported L3 services (L3 ISIDs) that can be terminated on this device.

Q: Furthermore, is it correct that the values of the smallest fabric node count?

1. Assuming there are only fabric nodes with 2000 BEB nodes per VSN and then a fabric node with a maximum of 500 BEB nodes per VSN is added. Then there can only be 500 nodes in this VSN, right?

A: This does not relate to the VSN as you can break the area up into multiple areas and then span your VSN further to more than 500 nodes. But yes, when it comes to number of nodes within an IS-IS area, this number has to be taken into account. But L2 ISID and L3 ISIDs are local per switch and not global numbers.

However, our guidance is that an area should not go beyond 500 nodes. If a smaller switch is used such as 5320 or 5420 it is recommended to depending on the amount of services to break the fabric up into smaller areas. This is what Multi-Area is for.

Q: 2. If there is a fabric with nodes that can have 4000 L2 VSNs and a fabric node with a maximum of 512 L2 VSNs is added. Does this affect the other nodes which can have a maximum of 4000 L2 VSNs? Does this also fundamentally reduce them to 512 L2-VSNs or only to the specific L2-VSN as in point 1.?

A: The number of VSNs a node supports does not have a direct link to the number of VSNs supported in a fabric. So if you attach a small switch at the edge of your network this would not impact the scale of your "larger" boxes when it comes to VSNs. 

You have to look at VSNs the following way: Each box that participates in a VSN starts its unique forwarding tree for broadcast traffic for each ISID. If you have 3 boxes with all sharing 4000 ISIDs you build 12k trees. The boxes that are in the "middle" of those 3 boxes will see 12k trees and need to support that many. Each tree is a L2 Multicast FIB entry. So a "small" box at the edge of the network will not know about those 12k trees, except it participates in some of those ISIDs. The number of supported l2 MC fib entries are documented per box.

Makes sense?

Roger

[Phil_]

Hi Jan,

1. Yes you are right, the weakest switch does limit the maximum number of nodes you can have. But you can solve this problem with the multi-area feature, which results in each area having a separate limit based on the weakest node in that specific area.

2. This is kinda tricky question, I would assume that it's not, I think that specific node would just stop detecting the i-sid or starts reporting a warning that the table is getting too big. But there is also the multi-area feature that can solve this problem.

Best regards,

Phil

[Shaja · Accepted solution]

Hi Jan 

You probably need to  reach your country SE they can explained that much better then I...

🙂

Let say we have a very big Enterprise or a ISP with 1000 sites or POPs.

In the local site you have some LAN switches with VLAN (100 200 300 400 500)  and 2 fabric nodes.

You can use the same L2VNS but I think it will be much more elegant to mach L2VNS  to the site ID.

Like that

Site 1 is Isid 1001 with vlan  100 200 300 400 500

Site 2 is Isid 1002 with vlan  100 200 300 400 500

  ISPs

Every  client could  a Isid or every POP service like Internet Voip IPTV.. 

POP 1 ISID 1001 Internet 

POP 1 ISID 1002 Voip

POP 1 ISID 1003 IPTv

 Those ISID or services can run as E-TREE that great for security 🙂