Subject: [nvo3] Suggested text about the path optimization issue to be added into the problem statement draft

From: Xuxiaohu <[email-masked]>
Date: Tue, 13 Nov 2012 07:57:09 +0000

Hi co-authors of draft-ietf-nvo3-overlay-problem-statement,

According to the suggestions made by some co-authors of draft-ietf-nvo3-overlay-problem-statement during the IETF85 meeting, I would like to suggest the following text about the path optimization issue to be added into the problem statement draft:

"VM migration across data centers usually require a LAN where the VM is located to be extended across these data centers. Since the LAN has been extended across multiple data center locations, the IP subnet associated with this LAN is also extended across these locations. As such, the traffic to/from the extended subnet (e.g., the traffic between cloud user sites and cloud data centers) would encounter suboptimal routing issues as described in the following sub-sections. Such suboptimal routing issue results in not only an unnecessary consumption of the bandwidth resources dedicated for data center interconnect, but also a possible decrease of cloud users' experiences due to increased path latency. Note that here the traffic to/from the extended subnet refers to L3VPN traffic between a remote L3VPN site (e.g., a cloud user site) and cloud data centers, rather than Internet traffic to/from cloud data centers. 

1.1. Suboptimal Routing for Incoming Traffic

Since the IP subnet has been extended across multiple data center locations, the location semantics of such subnet is lost. As a result, the incoming traffic towards a given server within the extended subnet may travel through suboptimal paths since the traffic is forwarded based on the corresponding subnet route. For instance, assume a server within a given subnet which has been extended across data center X and Y, is physically located at data center X, the incoming traffic towards that server may be forwarded to a default gateway router of that extended subnet located at data center Y before entering that subnet.

1.2. Suboptimal Routing for Outgoing Traffic

To avoid modifying a VM's default gateway address when migrating such VM across data centers, VRRP would usually be deployed between default gateway routers at different data center locations and therefore only one default gateway router would be elected as the VRRP Master for a given subnet that has been extended across these data center locations. As a result, assume one default gateway router at data center X is elected as the VRRP Master of a given subnet, the outgoing traffic originated from a given server of that subnet which is located at data center Y would have to be forwarded to that VRRP master at data center X through the extended LAN, which in turn forwards the traffic out of that extended subnet."

Best regards,
Xiaohu