Author: Valter Popeskic

If you check Juniper configuration guide for SRX firewall clustering, there will be a default example of redundancy-group weight values which are fine if you have one Uplink towards outside and multiple inside interfaces on that firewall.

set chassis cluster redundancy-group 0 node 0 priority 100
set chassis cluster redundancy-group 0 node 1 priority 1
set chassis cluster redundancy-group 1 node 0 priority 100
set chassis cluster redundancy-group 1 node 1 priority 1
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/5 weight 255
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/4 weight 255
set chassis cluster redundancy-group 1 interface-monitor ge-5/0/5 weight 255
set chassis cluster redundancy-group 1 interface-monitor ge-5/0/4 weight 255

This is the one: https://www.juniper.net/documentation/en_US/junos/topics/topic-map/security-chassis-cluster-verification.html

But if!

If you get to a situation where you may have multiple outside interfaces which are giving you Internet access or WAN access redundancy then maybe you don’t want failover to secondary SRX box to occur when you lose one of those two uplinks. If that’s the case, you should follow this article and get your SRX cluster to behave as it should.

This article describes the simplest way to enable MACSec using preconfigured static key-string. The example was tried on Catalyst 3850 and should work on other switches too.

There is another article that I wrote years ago which describes a more complex implementation with dot1x etc.

MACSec

Media Access Control Security is the way to secure point-to-point Ethernet links by implementing data integrity check and encryption of Ethernet frame.

When you configure MACsec on a switch interface (and of course, on the other switch connected to that interface), all traffic going through the link is secured using data integrity checks and encryption.

Data integrity is done by appending 8-byte header and a 16-byte trailer to the Ethernet packet which is generated before a data is sent and checked upon receiving on the other switch to prove that the data inside the frame was not modified on the way. If the check fails, the packet gets dropped.

Sometimes you will have some L2 domains (Bridge Domains – BD) in your datacenter that will be used with hardware appliances like F5 NLB or something like an additional firewall, WAF or something similar. That is the case where ACI will not route or bridge but the only L3 point of exit from that kind of segment would be on actual hardware appliance outside ACI Fabric – connected to the Leaf port.

We will take an example here and use it throughout the article where BIG IP F5 NLB is used as an L3 termination of L2 BD 10.10.10.0/24.

F5 is directly connected to ACI Leaf and routing from 10.10.10.0/24 subnet (L2 BD) is done directly on F5 device which is default gateway for that subnet endpoints.

In those cases for some particular implementations when you decide not to use PBR or Service graphs, it will happen that appliances like our F5 would become L3 termination for some ACI L2 BD like the 10.10.10.0/24 from my beautiful image above.

APIC Controller Cluster

You actually need three APIC controller servers to get the cluster up and running in complete and redundant ACI system. You can actually work with only two APICs and you will still have a cluster quorum and will be able to change ACI Fabric configuration.

Loosing One Site

In the MultiPod, those three controllers need to be distributed so that one of them is placed in the secondary site. The idea is that you still have a chance to keep your configuration on one remaining APIC while losing completely primary site with two APICs. On the other hand, if you lose secondary site, two APICs in the first site will still enable you to do configuration and management of ACI Fabric as nothing happened.

Losing DCI Interconnect

The second type of MultiPod fail is when you lose DCI (datacenter interconnect). In that case, both sites will keep working but will alert that the other side is down. The secondary site with one APIC will be in read-only mode and the primary site will be fully functional with two remaining APICs on that site. If some changes are made on the primary site, those changes will be replicated to the third controller on the secondary site when DCI recovers and configuration relating site B POD will be then pushed to POD 2 fabric.

DCI issues are not a good time for APIC replacement, just wait for DCI to start working normally and continue to use ACI APIC controllers as before the issues. You will still have the option to manage primary site if DCI fails and after DCI starts working again changes will be replicated to secondary site APICs and Fabric.

Please note that temporary DCI issues are not a good time to replace the APIC. If you are experiencing just a DCI outage the second site still works but it cannot be configured. Think about it, perhaps the best thing to do in this case is not to change the configuration of your fabric on either side while DCI doesn’t get back up and running. That way you are sure your configuration does not affect the MultiPod stability once DCI gets back up and sites start to communicate again.

This Cisco ACI article describes the first few things you will do when getting ACI Fabric components in your datacenter.

Cisco ACI 3.2 version was used to try the stuff described below

So let’s see what we have here:

Get Your Gear

In this one, we will get three APIC controllers, four Leafs and two Spines to build simple ACI and few 2060 switches for OOB management:

• 3x APICs APIC-CLUSTER-M2 – APIC Controller Medium Configuration (Up to 1000 Edge Ports)
• 2x Spines N9K-C9364C – Nexus 9K ACI & NX-OS Spine, 64p 40/100G QSFP28
• 2x SFP Leafs N9K-C93180YC-EX – Nexus 9300 with 48p 10/25G SFP+ and 6p 100G QSFP28
• 2x Copper Leafs N9K-C9348GC-FXP – Nexus 9300 with 48p 100M/1GT, 4p 10/25G & 2p 40/100G QSFP28
• 2x Catalyst 2960 OOB management switches

You need to cable Leaf and Spines in-between properly to form CLOS topology from the image below with 40G or 100G optics. Each Spine, Leaf and APIC controller needs to be connected to non-ACI OOB management network. You need then to connect redundantly APIC controllers to two Leafs with 10G optics and start the APIC initialization and fabric discovery.

Cable The Thing

Spines are all ports 40G/100G so you Choose your ports as you like, and for Leafs, each of them has last 6 ports 40G/100G so use one of those to connect to each Spine and you have your Leaf’n’Spine.

ACI Fabric with APIC