[j-nsp] Overlay physical interfaces and Overlay next-hop

[Phan Thanh Tung (FPT Smart Cloud)]

I am quite interested in the formula that calculates the number of next-hops and interface-number you provide as reference.

I would appreciate it if you could explain more clearly the parameters included in the above formulas corresponding to a specific context.

-----Original Message-----
From: Vincent Bernat [mailto:bernat at luffy.cx] 
Sent: Wednesday, March 24, 2021 2:01 PM
To: Phan Thanh Tung (FPT Smart Cloud) via juniper-nsp <juniper-nsp at puck.nether.net>
Cc: Phan Thanh Tung (FPT Smart Cloud) <tungpt15 at fpt.com.vn>
Subject: Re: [j-nsp] Overlay physical interfaces and Overlay next-hop

 ❦ 24 mars 2021 03:25 GMT, Phan Thanh Tung (FPT Smart Cloud) via juniper-nsp:

> Junos allows to re-allocate the maximum number of physical interfaces 
> and the maximum number of next hops reserved for use in an Ethernet 
> VPN-Virtual Extensible LAN (EVPN-VXLAN) overlay network.
>
> [edit forwarding-options]
> vxlan-routing {
>       interface-num integer;
>       next-hop integer;
>       overlay-ecmp;
> }
>
> https://www.juniper.net/documentation/en_US/junos/topics/reference/con
> figuration-statement/interface-num-edit-forwarding-options.html
>
> https://www.juniper.net/documentation/en_US/junos/topics/reference/con
> figuration-statement/next-hop-edit-forwarding-options-vxlan-routing.ht
> ml
>
>
> I don't know how to determine how many overlay physical interfaces and 
> overlay next-hop have been used.

There is a first hard limit of 16k virtual ports but you should stay below 12k. Check with:

request pfe execute command "show shim virtual vport" target fpc0 | count

For next-hop, you can use:

request pfe execute command "show nhdb summary" target fpc0

This does not differentiate between next hops for VXLAN and next hops for the remaining. If you increase the VXLAN one, you decrease the remaining next-hops available by the same amount. On QFX 5110, the maximum is 45000 for both. On QFX 5120, this is 61000. So, if you can manage a safe margin for both next hops, you are fine.

You can compute the number of next-hops manually with:

- overlay: ARPs resolved via local IRBs ARP + Remote IRBs (number of
  IRB per leaf*number of leaves) + Number of VRF with Type 5 * remote
  VTEP with Type 5 + 1
- underlay: 2 x Number of Layer-3 interfaces going towards each
  spine + (Number of local-trunk-ports * number of vlans allowed on
  each trunk port) + number of local access ports in each vlan + (Num
  of Leaf-nodes – 1) * number of VLANs + 7

For interface-num, this is the number of IRBs + number of routing-instances that have at least one active Type 5 tunnel.

Note, that was 2 years ago. Juniper has internal documentations about that, so it may be better to ask JTAC for updates, notably an easier command to get the result may be available.
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