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Pls. explain me how to see anycast from a looking glass BGP output
I am not very familiar with BGP, and I am trying to understand the output of looking glass to catch anycast networks.
For example, if I input 8.8.8.0/24 (this is for Google DNS) on http://lg.he.net and pick "Hurricane Electric Fremont 1" and "Equinix Ashburn (DC2)" and BGP Route, I receive two tables, one for core1.ash1.he.net> show ip bgp routes detail 8.8.8.0/24, the other for core3.fmt1.he.net> show ip bgp routes detail 8.8.8.0/24.
From there, I am a bit lost. Are all listed IPs possible IPs for google DNS? How do I see that 8.8.8.8 goes to different points for the two locations? Thanks!
Comments
It’s not always obvious if any casting is done correctly and the subnet announced from the same ASN.
You can try to figure this out from the traceroutes from multiple origins.
Talking about IP routing every router has a routing table containing the information which subnet should be routed to which next hop.
HE looking glass will show you different paths to a given destination when querying core routers in different locations.
However this only shows HE's next hop decision and does not prove that the given destination is announced from different POPs.
Like already mentioned, together with pings and traceroutes from various sources you can get an idea how the packets are flowing. For example when you see a RTT of <50ms to the same IP from the US and from EU, you can be sure that those packets are routed to (and the network announced from) different physical locations.
Thanks, I thought that anycast was visible from BGP, but I was wrong.
If you want a visualization of how traffic are flowing through the various AS, you can try:
http://lg.ring.nlnog.net/
The BGP map should give a nice visualization of how traffic flows from various different collectors that they have over the world.
Very interesting, thanks!