Active/Active ECMP

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Active/Active ECMP

L3 Networker

I have two Palo Alto 5250s running in my core network as a core firewall for all campus and datacetner traffic. They are running active/active. I have layer 3 routing south bound to two cat9500s not in VSS. So I am running HSRP on each 9500 alternating vlans to utilize them both. All 4 units are running OSPF to advertise loopbacks and iBGP is used to carry routes. The 9500s are setup for ECMP and so are the Palo Altos. I feel like there is some weird traffic issues with this, Should the Palo Altos even be setup with ECMP? If so should I be using the symetrical return option? Would having ECMP on the Cat9500s be enough to achieve load sharing/balancing over each layer 3 link to each Palo Alto? Each cat 9500 has a layer 3 link to each Palo Alto. And yes before people tell me Active/Active is not a good idea I cant see why not when my network is symetrical. 


Be aware, there are some pretty specific restrictions/caveats with floating IPs especially when it comes to NAT.  If you don't have asynchronous routing and you aren't utilizing ECMP, Active/Passive is the way to go.

Avoid the stacking because in-service upgrades give me PTSD. No NAT because they are Core Firewalls. Would like to use ECMP but it seems to be a headache. And even with Active/Passive and HSRP there is still the issue that there is a 50 percent chance that the active firewall will send the return traffic to the standby HSRP node. 


I'm lost on why you think you are going to hit the standby HSRP node? HSRP is going to give you an address that you can target as your next-hop address for routing. If you want to use HSRP, then you remove ECMP. If you want to use ECMP, then you remove HSRP. 

Yes, yes, and double yes.


Or you could stack your switches downstream from the 9500s and push Layer 3 out toward the access layer.  Then you would pretty much be using them as routers and you can ECMP all day long.

How do you figure? If each palo is learning each HSRP group VLAN via a routing protocol and both core switches own an SVI for that vlan, network is now connected. So OSPF will see the same subnet for a single vlan on each core switch as connected and based on ecmp will have a 50/50 shot of sending it the right node. 

I think we are just making recomendations based on lessons learned the hard way.  For me, HSRP is never a preferred solution.  I will only used it if forced to by some crazy Layer 2 limitation being imposed on me.  You do you man!

I was just trying to understand the question of why do I think the standby node would receive traffic. 

Dynamic routing and HSRP "can" lead to a very bad day.


Here is some reading.  Old but relevant.  For me, HSRP = too much headache.  We need to move beyond these Layer 2 limitations.  We have the routing protocols, "we can rebuild him... we have the technology..."  HAHA!


Hope this helps.

Read it. Labbed it. It works. But "routing" doesn't solve LAN side requirements for hosts all the time. Not every corporation is running nexus as their core, not every corporation is stacking or using VSS. "Routing" doesnt solve a gateway problem. 

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