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I'm looking at the latency from my machine to a world of warcraft server.

Every hop while I am in Comcast's network is sub 15ms.

Then it hits ATT and goes to 60-70MS for the rest.

Why would it suddenly jump from 15 to 60 considering it's still in the same city?

Is there anything I can do about it?

G-Man

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migrated from serverfault.com Apr 18 '10 at 7:30

This question came from our site for system and network administrators.

up vote 2 down vote accepted

Congested connection = long packet queue = latency
There's usually no way to avoid this besides switching your connection; even then other ISPs might use the same Upstream ISP.

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The inter-network link is slow. Not a damn thing you can do about it, short of switch ISPs.

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Unless Comcast is hiddlenly throttling traffic again. – geek Apr 18 '10 at 13:42

Remember that MPLS tagged networks report the ping time as the RTT for the virtual circuit. ICMP is also low priority, and, on a busy router can be dropped or delayed. Also, some routers enforce rate limiting and when ICMP gets over a certain threshhold, it'll drop/delay those packets as well.

Additionally, you could be experiencing an asymmetric route. Traffic that goes to that one router may return through a different route which may have more hops or congestion somewhere other than the path you see. So, when you hit that one AT&T router, their internal policies, or Comcast's route announcements may prefer a different ingress than the router the packet just exited.

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