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Is your network provider peered with Microsoft?

A key Microsoft recommendation for Office 365 performance is to get from your user to their network as quickly as possible. So in most scenarios, you ideally want local site internet breakout and that internet provider should be peered with Microsoft so that you have very few hops before your jump onto Microsoft’s network and then move over their network to your Office 365 tenant/service.

Peering is the direct interconnection between Microsoft’s network and another network for the purpose of exchanging traffic between these networks.

Microsoft’s primary Autonomous System number is AS8075. This is a unique number to allow the exchange of routing information with other network providers. Microsoft also manages the following ASNs: AS8068, AS12076.

You can look it up on PeeringDB and see some details about Microsoft’s peering relationships: Here you can see Microsoft’s public and private peering locations

Microsoft peer with over 2500 ISPs globally and have 70 points of presence where they peer with ISPs. So, in theory, your traffic should quickly pass from the ISP to Microsoft and onto their global network.

How can you see if your ISP is peered? Paul Collinge (Microsoft) explains on his blog, the simple way is a tracert to

Traceroute will actually send three packets of data and measure the time taken for each. It’s important to note that these times are not cumulative. The numbers returned are the round trip times taken for the packet to go from the originating machine all the way to the machine which kills the packet and returns the error message and back again. Routers tend to give timeouts and echo response handling lower priority than packet forwarding. This allows the switch to operate more efficiently as forwarding is much simpler to process than generating a new ICMP response. Hence the numbers do not increase in a linear fashion.

For example at home you can see I start on my router, then Zen my ISP, then to Microsoft in just 4 hops, and to Microsoft in London which is local to me, in between 11 and 39 ms.


PS C:\WINDOWS\system32> tracert

Tracing route to []
over a maximum of 30 hops:

1     1 ms     1 ms     1 ms  pfSense.localdomain [192.168.x.x]
2    45 ms    21 ms    40 ms []
3    10 ms    10 ms    28 ms []
4    11 ms    18 ms    39 ms []
5    13 ms    11 ms    20 ms []
6    69 ms    28 ms    29 ms []
7     *        *        *     Request timed out.
8     *        *        *     Request timed out.
9     *        *        *     Request timed out.
10     *        *        *     Request timed out.
11    35 ms    13 ms    13 ms

Trace complete.
PS C:\WINDOWS\system32>


You can see I route to London (lon04) then Cardiff (CWL20). Finally I land on an OWA server in Cardiff:

Other network codes:

  • ASH-Virginia
  • ATB-Georgia
  • LAX-Los Angeles
  • TYA – Tokyo
  • SIN-Singapore



About the author

Tom Arbuthnot

Tom Arbuthnot is Principal Solutions Architect at Unified Communications specialist Modality Systems. He is a Microsoft Certified Master and MVP, blogger, has a regular podcast with UCToday at and is a regular speaker at events including Microsoft TechEd and Ignite. He co-runs The Microsoft UC User Group London.

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Tom Talks Microsoft Teams and Skype for Business thoughts and news