Add 'VARP' as IP Role

[PieterL75]

NetBox version

v4.1.11

Feature type

Data model extension

Proposed functionality

Add 'VARP' as in IP Role.

Use case

This type is used on distributed EVPN layer3 networks, and provides and active/active IP on all EVPN leafs.
the current selection of IP Roles don't really covers this

Database changes

None

External dependencies

No response

[jnovinger]

What is the distinction between VARP and the existing VIP role?

[PieterL75]

a VIP is a 'floating' ip, active on one device of a cluster, and mainly referred to for load balancers.

a VARP is an IP that is active on multiple devices at the same time. There are no node-ips like with VRRP, only the VARP ip on the devices.
https://arista.my.site.com/AristaCommunity/s/article/active-active-router-redundancy-using-varp

[github-actions]

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[PieterL75]

I can write the PR is needed

[bctiemann]

Thanks @PieterL75 !

[pheus]

Thank you for the proposal. I have some reservations about adding a VARP role. It seems that VARP is an Arista-specific term for what is essentially an anycast gateway, as noted in the linked reference. Since we already have an “Anycast” IP role, it might be more consistent to stick with the existing, vendor-neutral nomenclature. While we could consider adding an “Anycast Gateway” role if needed, I believe it’s best to avoid vendor-specific names to prevent potential confusion.

[bctiemann]

@PieterL75 what do you think about changing this to be a more vendor-agnostic name like the "Anycast" suggested?

[PieterL75]

I checked 3 vendors on how they name the EVPN distributed router gateway intefaces:

• Cisco : Anycast gateway or Bridge Virtual Interface (BVI)
• Arista: Virtual-ARP (VARP)
• Juniper: IRB virtual gateway IP address (anycast)

I would like to keep the difference clear between a BGP Anycast IP (one IP living on multiple locations, announced over BGP)
and an ARP/VirtualMAC based EVPN Gateway.

What about EVPN VirtualIP, as this will be mainly seen in EVPN deployments

[jeremystretch]

I can't recall ever hearing the term "anycast" used with regard to local segment first-hop routing; as suggested, I'd avoid using it here.

[pheus]

I agree that it might be a good idea to differentiate between the “classical” anycast IP address and the first-hop IP address in a BGP EVPN VXLAN fabric. However, the more common term—even though no standard has been established—is "distributed IP anycast gateway." Keep in mind that in a layer 3/routed underlay, the first-hop IP address is distributed via BGP (in the case of a BGP EVPN VXLAN fabric). In fact, even the link provided by the author refers to an "anycast gateway." A quick search for "anycast gateway" reveals multiple discussions regarding BGP EVPN VXLAN fabrics, reinforcing that this term is widely used in practice.

Personally, I would suggest going with "Anycast Gateway" for clarity and consistency.

Of course, as the lead maintainer does have the final say, this perspective should be considered alongside the broader community's usage.

There are IETF documents that reference this concept:
https://datatracker.ietf.org/doc/rfc9135/
https://datatracker.ietf.org/doc/draft-malhotra-bess-evpn-centralized-anycast-gw/

[pheus]

I'd like to highlight why the term "Anycast Gateway" makes complete sense. Consider a BGP EVPN VXLAN fabric, which often features a typical spine-leaf architecture in a data center. In this design, where a Layer 2 segment is extended over a Layer 3 underlay and multiple nodes share the same gateway IP address, it is very useful to route traffic at the nearest node holding that gateway IP address. This is exactly the kind of scenario that an anycast IP address is meant to address.

[PieterL75]

I disagree that the IP is distributed over BGP in an EVPN fabric and then used as a destination IP for the endhost.
The IP is made available to the endhosts via ARP and not BGP. That said...

I don't see this as an Anycast system, but rather a distributed ARP/layer2/IP

I would go for a less confusing EVPN VirtualIP or EVPN Virtual Gateway

[pheus]

But I think we do agree on the key aspect here: the same IP address exists multiple times within the same Layer 2 segment, distributed across multiple nodes. And only the node nearest to the source responds to the ARP request and routes the traffic.

To me, this behavior matches very well with the fundamental concept of an anycast IP.

That’s why I still feel Anycast Gateway is a fitting and commonly understood term for this scenario.

[pheus]

I’d like to correct myself regarding my earlier statement about there being "no standard" term for this concept.

RFC 9135 (Integrated Routing and Bridging in Ethernet VPN (EVPN)) actually refers to this as "anycast default gateway IP" (Section 4.1).

“All the PEs for a given tenant subnet use the same anycast default gateway IP and MAC addresses.”

This matches exactly the use case we’re discussing here: multiple nodes (PEs) within the same EVPN fabric using the same gateway IP address — effectively providing an anycast gateway for the connected hosts.

Reference: https://datatracker.ietf.org/doc/html/rfc9135#section-4.1

This further reinforces my opinion that Anycast Gateway (or Anycast Default Gateway) is an established and technically correct term in the context of EVPN.

Hope this helps clarify my position!

[PieterL75]

I do follow the reasoning that this is a gateway that is 'multiplied' and resembles the logic of Anycast.
But as Anycast is commonly known and used for BGP announced IP's on global scale, it could confuse when a Layer2 local gateway is also referred to as 'Anycast gateway'

let's add EVPN then..
EVPN Anycast Gateway
(Dont add Default, as you don't know if that IP is the default for a subnet or just 'a' gateway)

[pheus]

Thank you, @PieterL75, for taking the time to engage in this constructive discussion with me — I really appreciate the exchange of perspectives.

I absolutely understand where you’re coming from. While anycast is indeed often associated with globally routed IPs, I think it's great to see these concepts and technologies making their way into local fabrics as well.

Personally, I’m perfectly fine with EVPN Anycast Gateway and agree that leaving out Default makes sense here.

Looking forward to the final decision from the maintainers!