DHCP DORA Explained with a Real Packet Capture
Discover, Offer, Request, Ack. You can recite DORA in your sleep, and it still will not help you the day a client comes up with a 169.254 address and the server insists the pool is fine. What helps is
Cisco
Platform-level material spanning multiple Cisco product lines. Licensing, hardware behavior, boot and upgrade paths, and the details that differ from the documentation.
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OSPF Hello Packets Explained with a Real Capture
Every OSPF adjacency you have ever built started with a Hello packet, and almost every adjacency that refuses to build is a Hello packet being quietly thrown away. The trouble is that show ip ospf neighbor only tells you the
Testing MTU With Ping and the DF Bit
Find the path MTU with nothing but ping, from Linux and IOS XE, against a real 1400-byte link. The 28-byte math and the PMTUD black holes that hang TCP.
Cisco Extended Ping and Response Characters Explained
Source interfaces, the DF bit, repeat counts, and the response characters (! . U M) that tell you exactly what failed. Extended ping on Cisco IOS XE, captured live.