Hands-on Junos CLI tutorials, OSPF and BGP configuration guides, SRX firewall policies and step-by-step network troubleshooting — lab-tested by working network engineers preparing for JNCIA, JNCIS and beyond.
Latest Guide
The EX alarm /var partition usage is high usually means leftover install images, old package sets after an upgrade, runaway logs or core dumps. This guide gives the checks in order, ranks the causes by how often they happen, and shows which files are safe to delete and which are not.
Read full guide →
When Junos DHCP relay is not working, the drop counters in show dhcp relay statistics usually name the cause. This guide explains each counter, gives checks in order from cheapest to most expensive, and ranks the causes by how often they happen. It includes copy-ready EX and SRX configs and shows healthy output.
A Junos irb interface down with the Hardware-Down flag is a Layer 2 problem. The IRB only comes up when its VLAN or bridge domain has at least one member port that is up and forwarding. This guide gives the checks in order, ranks the causes, and shows healthy and broken output.
'High memory utilization on our core switch' is a permanent r/Juniper thread — and the JTAC answer surprises people: EX4600/EX4300 sitting at 75% is by design. Here is how to tell normal pre-allocation from a genuine leak, and the fixes for each.
Two leafs, two spines, multihomed hosts — and the ping fails. The r/Juniper EVPN-VXLAN ping issue scenario, solved methodically: underlay reachability, MAC learning, ESI multihoming, IRB gateways and overlay verification tools.
An IDP policy attached to a security policy does not mean traffic is inspected. The community thread 'Either configure idp or idp-policy and not both' shows the confusion — here is how IDP actually engages and how to verify inspection is happening.
The upgrade command fails with validation failed or the install aborts midway. Learn how Junos validation works, how to find the exact unsupported config statement, free disk space, and when no-validate is safe.
SRX security flow traceoptions show every decision the flow engine makes: session lookup, NAT, route, zone and policy. This guide covers the cheaper checks to run first, monitor security packet-drop on newer releases, how to read a trace line by line, and the root causes ranked by how often they bite.
A Junos ISIS adjacency stuck in Initializing means one router hears the other, but its own hellos are not being accepted in return. This guide gives the ordered checks, ranks the root causes from missing family iso to hello padding and ISO MTU, and shows healthy and broken output.
A Juniper EX BPDU error means a BPDU-protected port received a spanning tree BPDU, so Junos shut it down until someone clears it. This guide shows how to confirm the error, find the source, clear it on ELS and non-ELS switches, and set auto-recovery without creating a flapping loop.