Advantages of Anycast Gateway

[EF]

Hi Team,

I was reading about this new feature introduced in release 9.1 that can be used to replace VRRP (which is currently my preferred option for L3 redundancy).

I have some doubts because I think I'm missing something.

What are the real advantages of Anycast Gateway? In which scenarios is it a better option than VRRP? What kind of topology is the best fit for this feature?

Thanks in advance!!!

EF

[Ludovico · Accepted solution]

If your access switches are running SwitchEngine as FA Proxies, and you have VRRP with backup-master on the FabricEngine FA Server MLAG pair, then VRRP with Backup-Master is still perfect as you will get active-active load balancing of routed traffic on both VRRP routers (Anycast Gateway - ACGW - will also work fine).

Where ACGW shines is when the access switches are running FabricEngine. If you run VRRP here, the backup-master function becomes ineffective as the the fabric access switch will have to MAC-in-MAC encapsulate all VRRP gateway MAC destined traffic towards the real owner of the VRRP MAC i.e. only the VRRP Master router will be routing that traffic onwards, so you get no load balancing; also in certain fabric  topologies the VRRP Master router might not be the nearest, so the forwarding path might be sub-optimal.

With ACGW, the fabric access switch can see if there are more ACGW gateways for the L2 I-SID (VLAN) and will deliver the traffic to the nearest gateway. If both/all gateways are equally near, then traffic from the different I-SIDs will be balances among them.

But ACGW requires some intelligence from the FabricEngine access switch which is a L2 switch. You need all FabricEngine devices to be on VOSS 9.1.0.0 or later.

[CordScott]

To clarify, only the Fabric Engine devices hosting anycast gateway ip's need to be running 9.1 or later? This is my understanding of it. This is not like the internal route tags that will crash devices running older firmwares. 

[Ludovico · Accepted solution]

No, you need 9.1 or later on all the access L2 fabric nodes where you will be terminating L2VSN (VLANs) which are configured with an Anycast Gateway IP on the Core/Distribution nodes.

If you have access switches with an older software version, and you extend L2VSNs with Anycast Gateway, these nodes will not be able to program the Anycast Gateway MAC, and all user traffic destined to the Anycast Gateway MAC will get flooded; you don't want that!

[CordScott]

Thanks. That makes sense. What about access switches/BCBs where the l2vsns that are mapped to the anyccast gateways are not terminated? Any issues there? Traffic just forwarded normally?