CUNP case studies
CUNP · Put your knowledge to work in context.
The Certified Unix Network Professional (CUNP) is a vendor-neutral credential aimed at administrators who already run Unix-like systems day to day and now need to prove they can design, configure, secure, and debug the network layer on those systems. It suits mid-level sysadmins, NOC and infrastructure engineers, and DevOps practitioners whose work spans Linux or BSD hosts, daemons, packet filters, and routing tables. The CUNP case studies are 5 cases and about 4,393 words.
1Dual-Homed Host on a Shared Broadcast Domain
A Debian 12 host named edge-relay has two 10 GbE NICs: ens3f0 at 192.0.2.10/24 and ens3f1 at 192.0.2.11/24, both with default gateway 192.0.2.1 on the same L2 segment. The upstream switch ports were both left as access ports on VLAN 40 after a migration, so the interfaces share a broadcast domain.
872 words, about 4 min2nginx and PHP-FPM at 18,000 Connections
An Ubuntu 22.04 web tier runs nginx 1.24 in front of PHP-FPM 8.2 on eight 4 vCPU/16 GB nodes behind an L4 load balancer. Each node peaks at 18,000 established client connections and 60,000 requests per minute; keepalive to upstreams is enabled.
833 words, about 4 min3Two WANs, Conntrack Full, and One-Way VoIP Audio
A Linux router (Debian 12, kernel 6.1) provides NAT for a 2,000-host branch over two ISP links: wan0 (203.0.113.2/30, 1 Gbps) and wan1 (198.51.100.2/30, 300 Mbps). nftables performs source NAT, and a policy rule marks UDP 16384-32767 with fwmark 0x1 and routes it via a table pointing at wan1; all other traffic uses wan0.
865 words, about 4 min4LDAP Certificate Rotation Breaks SSSD and Local sudo
A RHEL 9 fleet authenticates SSH users through SSSD against an OpenLDAP directory, with PAM requiring a TOTP token via pam google authenticator after the password. nsswitch.conf has passwd: files sss and sudoers: files sss .
825 words, about 4 min5MTU 9000 Rollout Script Fails at Host 73
A platform engineer wrote a 70-line bash script to roll out MTU 9000 on the storage network across 200 hosts. It reads hosts from a CSV, loops for h in (cat hosts.txt) , runs ssh -o BatchMode=yes root@ h "ip link set ens5 mtu 9000 && systemctl restart nfs-client" , and starts with set -euo pipefail .
998 words, about 5 min