Thursday, January 20, 2011

Determine the latency to a SixXS Point of Presence

I've recently moved from NL to the UK and was looking at my SixXS IPv6 link. I wanted to make sure I'm getting the best connection possible, so went about checking the latency between my endpoint and the PoPs.

First - I did a simple mtr to my existing PoP in NL, then to the only UK based PoP. This initial test showed the latency to my existing endpoint was around 23ms, while it was around 30ms to the local UK based PoP. This doesn't seem right, so dig further.

mtr --psize=1496

mtr uses ICMP echo requests to determine latency. By default these are 56 bytes, which is an unrealistic packet size for determining latency practical between two points. Once the packet size was set to something more reasonable, such as --psize=1496, then I saw less latency to the UK PoP.

mtr --psize=1496

Aside from using mtr, there is another way to get a broader idea of latency between your endpoint and the available PoPs. The PoPs page at SixXS has a list of all currently active pops. Using this, here's a one-liner to fping all of them and quickly determine your best link:

wget -q --no-check-certificate -O - | grep -Eo '[a-z]{5}[0-9]{2}' | grep -v xhtml | sort -u | while read PoP; do echo -n "$ "; done | xargs fping -i 100 -p 50 -b 1208 -c 50 -n -s -a

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