OSPF Sequence Numbers When an OSPF router originates an LSA for the first time, it will choose the sequence number 0x80000001. The 0x prefix means it’s a hexadecimal number, where each hex character represents a four bit binary word. This post discusses why the OSPF sequence number begins with 0x8, and some quirks when counting with signed numbers.
Designed to fail Security audits are a fantastic way to improve the security of your network. A good auditor can highlight critical flaws in your design and configuration before they are launched into the big bad world. However I think there is a massive issue with security audits; they are designed to fail.
Unicast Hello packets I was debugging an issue recently and ran across something unusual. I had thought that all OSPF hellos on BCAST and P2P intefaces were sent as multicasts. However as you can see from the wireshark capture below, packet 10 is clearly sent as a unicast. # Time Source Dest Proto Info 04 15.503997 192.168.12.2 224.0.0.5 OSPF Hello Packet 09 23.507483 192.168.12.1 224.0.0.5 OSPF Hello Packet 10 23.518430 192.168.12.2 192.168.12.1 OSPF Hello Packet 14 25.400245 192.168.12.2 224.0.0.5 OSPF…
We’re in the midst of a networking boom at the moment and new technologies are being released at a rapid pace. So much so that network engineers need a suite of knowledge management tools to navigate the daily deluge of articles, documents, twikis and notes. That said, how much of your day-to-day activities are markedly different than they were two years ago? As I see it, the role of the network engineer is largely unchanged. One still has to gather…
A test – What LSAs will broadcast interfaces generate? You have just added a new workgroup switch, switch_1 to your network. You have the following conditions. Router_A and Router_B were already fully adjacent over an OSPF point-to-point link. Network 192.168.12.0/24 is immediately advertised by Router_A to Router_B. There are no other OSPF routers connected to Switch_1. Router_A interface Gi1/0 is up/up, has OSPF network-type BCAST and has assumed the role of DR for that segment. My question to you is,…
When a single-homed router is isolated by link failure, the LSAs it had previously originated can live for up to 60 minutes in the OSPF LSDB of the surviving routers. This may not be what you were expecting, and can cause a lot of confusion when troubleshooting OSPF. In this post we’ll look at why LSAs from an isolated router linger and how OSPF still knows how to ‘do the right thing’.