Networking Nonsense

From not knowing what an IP address was to being utterly in love with networking. I’ve finished the CCNA/CCNP track and I’m currently wrapping my head around the CCNP ENCOR material. Nothing beats the dizzy little thrill when a stubborn network finally works.

Lab Recipes Troubleshooting Flows Config Snippets
IPv6 VLANs OSPF BGP BFD QoS Wireshark

The Philosophy

Design simply, document clearly, verify ruthlessly. If you can diagram it, you can fix it.

My principles

The Grind

Labs, breakage, packet captures, repeat. CCNP made me love the “why,” not just the “how.”

Build a lab

The Payoff

That moment the last route shows up and pings turn green. Dizzy? Yep. Worth it? Always.

See the flows

Principles I work by

  • 📐 Keep topologies boring. Boring is fast to debug.
  • 🗺️ Draw it first; build it second; document it last (but do document it).
  • 🧪 Change one thing at a time and verify with multiple signals (CLI + PCAP + monitoring).

Lab Recipes (bite-sized)

# VLAN & Trunk sanity (IOS)
conf t
 vlan 10,20
 exit
 interface g0/1
  switchport mode trunk
  switchport trunk allowed vlan 10,20
  spanning-tree portfast trunk
end
show int trunk
show vlan brief
# OSPFv2 minimal (IOS)
conf t
 router ospf 10
  router-id 1.1.1.1
  network 10.0.0.0 0.0.0.255 area 0
end
show ip ospf neighbor
show ip route ospf
# BGP peering (IOS)
conf t
 router bgp 65001
  bgp log-neighbor-changes
  neighbor 192.0.2.2 remote-as 65002
  address-family ipv4
   neighbor 192.0.2.2 activate
   network 10.10.10.0 mask 255.255.255.0
  exit-address-family
end
show ip bgp sum
show ip bgp
# Quick BFD for BGP stability (IOS-XE)
conf t
 bfd-template singlehop BFDFAST
  interval 50 min_rx 50 multiplier 3
 !
 interface g0/0
  bfd echo
 !
 router bgp 65001
  neighbor 192.0.2.2 fall-over bfd
end
show bfd neighbors detail

Troubleshooting Flows

  1. Scope it: single host, VLAN, site, or WAN?
  2. Basics: link up, switchport correct, VLAN present, trunk allowed?
  3. Layer 3: default gateway right, ARP sane, route present?
  4. Control plane: OSPF/BGP neighbors up, timers and filters correct?
  5. Data plane: ACL/NAT/QoS interfering? Asymmetric path?
  6. Proof: counters + PCAP + traceroute agree? Then document the fix.

Useful Snippets

# Switchport cleanup (IOS)
default interface range g1/0/10-24
interface range g1/0/10-24
 switchport mode access
 switchport access vlan 20
 spanning-tree portfast
 spanning-tree bpduguard enable
# IPv6 quick check (IOS)
show ipv6 int brief
show ipv6 route
show run | sec ipv6
# Wireshark display filters
ip.addr == 10.10.10.10
tcp.flags.syn == 1 and tcp.flags.ack == 0
dns and ip.addr == 192.0.2.53
# Linux edge check
ip -br a
ip r
ss -tupn
tcpdump -i eth0 -nn -c 50