An Oracle blog about ZFS Storage

  • April 19, 2012

Route Table Stuff

Steve Tunstall
Principle Storage Engineer

Let's talk about your Routing Table.

I have never installed a ZFSSA, ever, without having to edit this table. If you believe that you do not need to edit your routing table, then you are wrong.
:)  Ok, maybe not. Maybe you only have your ZFSSA connected to one network with only a few systems on it. I guess it's possible. Even in my simulator, however, I had to edit the routing table so I could use it no matter how I had my laptop connected, at home over a VPN or at work or using a public Wifi. So I'm going to bet a nice dinner that you, or someone, should be checking this out.

First things first. I'm going to assume you have a cluster. I try really hard to only sell clusters, but yes I know there are plenty of single-nodes out there too. Single-node people can skip these first two paragraphs. It's very important in your cluster to have a 1GigE management interface to each of the two controllers. You really want to be able to manage each controller, even when one of them is down, right? So best practice is to use the 'igb0' port for controller 1 management and to use the 'igb1' port for controller 2 management. It's important to make these ports 'Private' in the cluster configuration screen, so they do NOT failover to the other controller when a cluster takeover takes place for whatever reason. Igb0 and igb1 are two of the four built-in 1GigE ports. You can still use igb2 and igb3 for data, either alone or as an aggregate, and don't make them private, so they DO failover in a cluster takeover event. Now go to your remote workstation, which may be over a different subnet, and you should be able to ping and connect to Controller 1 using igb0.
Now, back to the routing table. You have probably noticed that you can not ping or connect to the other controller, and you think something is wrong. Not to worry, everything is fine. You just need to tell your routing table, which is shared between the heads, how to talk to that other port, igb1. You see, you have a default route setup already for port igb0, that's why it works. Your new, private, igb1 however, does not know how to speak back to your remote system you are now using to manage via the BUI from a different subnet. So, make a new default route for igb1 and point it to the default gateway, which is the router it needs to use in order to cross subnets. See the picture below. Note how I have a default route for "ZFS1-MGMT" for port igb0. This shows a green light because I'm currently on ZFS1, and it sees this port just fine. I also have a default route for "ZFS2-MGMT" from port igb1. This route has a blue light, showing it as inactive. That's because this controller, ZFS1, has nothing plugged into it's igb1 port. That's perfect. Hit "Apply". Now count to 10. Now from your remote host, go ahead and ping or connect to Controller 2, and it works!!! This is because your controllers share a routing table, and when you added that igb1 route, it propagated over to the other controller, where igb1 is plugged in, and that route has a green light over there and it works fine. You will see from Controller 2's point of view that igb1 has a green light and igb0 has a blue light.  (continued below the picture)

Now it's time to setup any static routes you may need. If you have different subnets for your 1GigE management and your IB or 10GigE data (a very good idea), then you will need to make these. It's important to have routes for this, as you do not want data coming in over the 10GigE pipe, but then returning over the 1GigE pipe, right? That will happen if this is not setup correctly. Make your routes, as the picture example shows with a 10Gig aggragate here we called "Front-end-IP". Any traffic coming in from subnet 172.20.69 will use this pipe.

Lastly, check your multi-homing model button up top. I like 'Adaptive'. Loose is the default, and makes it so your packets can traverse your routes, even though they may go over the wrong route, so it seems like your system is working. This can very well be an illusion. Your ping may work, but it may be coming from the wrong interface, as "Loose" basically means the ZFSSA just doesn't care or enforce any rules. "Strict", on the other hand, is great if you want total enforcement. If you are very good with your routes, and are positive you have it right, and want to ensure that a packet never goes the wrong way, even if that means dropping the packet, then use Strict. I'm using Adaptive here, which is a happy medium.  From the help file: The "Adaptive" choice will prefer routes with a gateway address on the same subnet as the packet's source IP address: 1) An IP packet will be accepted on an IP interface so long as its destination IP address is up on the appliance. 2) An IP packet will be transmitted over the IP interface tied to the route that most specifically matches an IP packet's destination address. If multiple routes are equally specific, prefer routes that have a gateway address on the same subnet as the packet's source address. If no eligible routes exist, drop the packet.

Update 4/23/12- My colleague, Darius (https://blogs.oracle.com/si/), rightfully wanted me to point out how important it was to setup a static route for replication. You do not want replication to go over a private management port by mistake, as this will cause it to fail when one controller or the other goes down for maintenance.

I hope this helps. Routing can be fun. 

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