When I wrote something like this, it ended up being very complex. I am a network guy, so you'll need to bear with me for a minute. There are protocols that allow a set of routers to act like one router (VRRP, HSRP). Cisco's HSRP happens to like flip-flopping, so traceroute likes to reports both addresses/routers on the same line. Names can change too easily, so I didn't do any processing with names, just on the IP addresses. But, when I got two addresses on a single line, I created a group and later considered any address within that group to be equivalent.

In my scheme, your example has one difference, the additional route toward the bottom. I don't remember the difference logic very well, but it was convoluted.

Well, months went by, I finally went in and did some sanity checking with the groups, and there were some major problems. It ended up having a very large group of like 30 addresses it considered equivalent. Unfortunately that made lots of the "hops" within a traceroute equivalent. ie a traceroute might end up looking like this after processing: hop1, hop2, group12, group12, group12, hop6, destination. Where those three group 12's in the middle were representative of different routers that had been grouped together as being equivalent by my code.

I'll try to dig that code up after lunch and either post some of it, or at least give you a better feel for the difference logic I'd used.

Update: Seems my difference code was very simplistic, aside from the "group" checking. Go through each traceroute in lockstep, and if they're different, add one to the difference count. I'd had a comment to improve that to make it more "diff-like", but I never got there, sorry.

-Scott

In reply to Re: how to count route diffs in traceroute outputs by 5mi11er
in thread how to count route diffs in traceroute outputs by clint

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