All of the Pings!

Ping is one of the most recognised network troubleshooting tools. It is used without thought and is considered so basic that to post about it seems pointless, however, pings aren’t pings!

Ping started as a small utility written by Mike Muuss who was working at the Ballistic Research Laboratory and needed a quick and easy way to troubleshoot the state of the network. Given the tools usefulness it has since been ported to many platforms.

Ping uses the Internet Control Message Protocol (ICMP) to send ICMP Echo Requests to the target host and listen for ICMP Echo Replies. If you want to learn more about ICMP, check out RFC 792

Ping is useful for the following reasons:

  • It can assist in detecting network reachability of a host (However it can be confusing if there are return path issues .. )
  • It is useful as a “yard stick” for network performance by looking at the Round Trip Time (RTT) (Latency), the degree that the RTT changes (i.e. Jitter) and the rate of packet drops (if any)
  • To discover devices on a network (nmap –sP –PN!)
  • To discover any MTU limitations and network performance issues that can result

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From Scratch #3: Redistributing Between OSPF and BGP

This is a pretty common scenario. You are running and IGP (in this case, OSPF) on your local network and you connect to another company or ISP via an eBGP link.

Your goal is to leak some of the external routes received via BGP into your IGP, and in turn leak some of your internal routes out via BGP. The constraint is you don’t want everything. Only the routes you decide.

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