Implementing SES Network Duplication A Best Practices Guide.

Transcription

1 Implementing SES Network Duplication A Best Practices Guide. SIP Enablement Services 5.1 Avaya ABSTRACT This application note is a tutorial on Avaya SIP Enablement Services Network Duplication from an implementation focus. SES Network Duplication basics, protocol examples and rationale are discussed as a Best Practice. The customer is always free to implement SES Network Duplication in any other method they choose for any reasons. The intent of this document is to provide guidelines on implementing Avaya s SES Network Duplication from a best practices data network view. External posting: Application Note Issue 2.0 Issue 1.0 Initial Release Issue Added Bandwidth Requirements December 2008 COMPAS ID BH and MJK 1

2 All information in this document is subject to change without notice. Although the information is believed to be accurate, it is provided without guarantee of complete accuracy and without warranty of any kind. It is the user s responsibility to verify and test all information in this document. Avaya shall not be liable for any adverse outcomes resulting from the application of this document; the user accepts full responsibility Avaya Inc. All Rights Reserved. Avaya and the Avaya Logo are trademarks of Avaya Inc. or Avaya ECS Ltd., a wholly owned subsidiary of Avaya Inc. and may be registered in the US and other jurisdictions. All trademarks identified by and are registered trademarks or trademarks, respectively, of Avaya Inc. All other registered trademarks or trademarks are property of their respective owners. Questions and comments should be directed to: bhoward@avaya.com or afunguy@avaya.com Table of Contents 1) Introduction...3 2) SES Network Duplication Basics...3 3) L2TPv3 Protocol Rationale...3 4) Physical vs. Logical WAN Views...4 5) L2TPv3 Header...5 6) Traffic Pattern Considerations...6 7) Bandwidth Considerations...7 8) Configuration and Verification...8 9) Best Practice Checklist ) Related Documents...11 BH and MJK 2

3 1) Introduction This application note is a tutorial covering the Avaya SIP Enablement Services (SES) Network Duplication from a network implementation focus. SES Network Duplication basics, protocol rationale, configuration and verification are discussed and summarized as a Best Practice checklist. Customer s may implement SES Network Duplication using other methods but these notes only document the method we believe is a best practice. However, Avaya will diagnose and fix any customer s network for a fee through Avaya s Global Services. The intent of this document is to provide guidelines on implementing Avaya s SES Network Duplication from a best practices data network view. Network Duplex configuration (Geo-Redundancy) provides mission critical duplication similar to the cabled duplex configuration. With SES Network Duplication, whether edge, home or home/edge combo, the two SES servers can be physically separated via WAN routing. This allows the SES servers to be placed anywhere in the world. 2) SES Network Duplication Basics When using SES Network Duplication mode, the two SES servers must be on the same LAN network or subnet. SES Network Duplication is an OSI model layer-2 solution. SES Network Duplication servers, whether edge, home or edge/home combo, share a virtual IP address. L2TPv3 is used to connect the two SES servers over a WAN and is essentially a pseudo-wire across that WAN. L2TPv3 was intended to bridge a WAN to connect two halves of the same network or subnet. Redundancy options include: Redundant edges with single home Redundant homes with single edge Redundant homes and redundant edges (whether combo and separate servers) 3) L2TPv3 Protocol Rationale There are several choices when selecting a bridging protocol to tunnel layer-2 traffic across a WAN. L2TPv3 was selected as a best practice because: It is easy to configure Point-to-Point only connectivity is needed It supports modern L2 WAN protocols including: o Ethernet o Frame Relay o ATM o MPLS o PPP Current vendor support (Cisco and others) RFCs are available L2TPv3 is not a proprietary protocol Tunnel endpoints do not have to be on the WAN edge routers Provides security guarantees against spoofing BH and MJK 3

4 4) Physical vs. Logical WAN Views Effectively, the WAN transport and perhaps some LAN network devices become transparent from a logical view as shown by the two diagrams below. BH and MJK 4

5 5) L2TPv3 Header The L2TPv3 header is a shim consisting of two parts and is 8 to 16 bytes depending on automatic or manual implementation modes. Below is a view of automatic L2TPv3 frames as shown by Wireshark a freeware protocol analyzer. This means anyone can easily identify and troubleshoot L2TPv3. As you can see, between the IP and Application layer resides the L2TP and the Default sub-layers. This capture was taken from an Ethernet segment, but a WAN capture would look the same except for the layer-2 protocol. An expanded view (below) shows the details of the L2TPv3 and Sub-layer contents. Each L2TPv3 frame has a session ID and a magic cookie. The sub-layer contains the s bit and a sequence number. The session ID will remain the same during the life of the session. The sequence number will remain the same during the session unless there is a server interchange. Details about L2TPv3 can be found in many places on the Internet. Two good information sources are: RFC BH and MJK 5

6 6) Traffic Pattern Considerations Most implementations will have phones located at both the Primary (active) and Stand-by SES servers. If the number of phones is relatively balanced at both locations, the bandwidth needed before and after an SES server interchange will remain about the same. This is important for sizing the WAN bandwidth needs with the Service Provider. Conversely, placing most or all of the phones at one site will have a dramatic effect on WAN bandwidth. Consider the diagram below: BH and MJK 6

7 7) Bandwidth Considerations Bandwidth is measured in Busy Hour Call Completions (BHCC). BHCC represents the number of calls initiated and completed in the busiest hour of a company s phone traffic. The chart below shows bandwidth needed for 1,000 to 15,000 BHCC. The bandwidth needs are very linear and represent call signaling only. Bearer traffic, as a best practice, should not be on the same network as the SES servers. If you chose to include bearer traffic, you must increase the bandwidth significantly. Server interchange events take very minimal bandwidth and do not need any additional bandwidth consideration. Finally, when a new or replaced SES network duplication server is added, the entire database contents of the active server are sent to the stand-by server. This is best done out of business hours. The time and bandwidth needed depend on the number of SIP phones on the system. 800 SIP phones will take about 2-minutes at 1200Kbps bandwidth. SES database transfer is TCP based which will adapt to your available bandwidth. A pair of DS-1 circuits may provide enough bandwidth for most customers. The other benefit of using at least one pair of DS-1 circuits is that it eliminates a single point of failure in the WAN. More than two DS-1 circuits may be desirable to provide redundancy and enough bandwidth in the event of a WAN outage. BH and MJK 7

8 8) Configuration and Verification BH and MJK 8

9 Configuration Steps Enable IP CEF Step #1: Each router needs to have IP CEF enabled. This is a layer 3 switching technique that speeds processing of packets from the ingress to egress interfaces. Interface Loopback 0 Step #2: The Loopback interface is the terminating point for the L2TP traffic. Each router Loopback must be reachable from the other router. This can be accomplished with static routes or routing protocols. Configure L2TP Control Channel Step #3: This creates the L2TP Class which is a template that is inherited by the different pseudowire classes. The class includes parameters such as authentication, keepalive timers, and retransmission timeouts. In this example, only authentication is configured, the other parameter default values are acceptable. Configure L2TP Pseudowire Step #4: The pseudowire is a template that defines the data encapsulation type, control protocol, signaling, and sequencing. My example configures the encapsulation type as L2TPv3, and assigns interface loopback 0 as the source IP address for tunneled packets. Authentication is configured by assigning the geo-class Control Channel template. IP ToS Reflect assigns the inner IP packet ToS setting to the tunneled packet. Configure Xconnect Circuit Step #5: This binds the interface G0/1.16 (VLAN 16) to the L2TPv# pseudowire. The command is broken down and explained: xconnect keyword to assign binding remote end loopback IP 10 virtual circuit ID used between the near end and far end routers. The value must match on each router. pw-class geo-pseudowire template used to assign pseudowire template. BH and MJK 9

10 Verification Steps Displays detailed information about all current L2TP sessions configured on the router. Displays information about all current L2TPv3 sessions, including peer router IP address, and circuit status. Displays information about all current L2TPv3 sessions and their protocol state, including remote virtual circuit identifiers. *Note: Circuit ID must match on the near and far end router. BH and MJK 10

11 9) Best Practice Checklist Place SES servers on their own network (subnet) to avoid transporting needless broadcast traffic across the WAN. Use L2TPv3 as the preferred bridging protocol. See section 3 for the rationale list. Distribute the number of phones registered to SES between SES locations to balance the WAN traffic regardless of which server Provide routing at both SES locations to provide normal operations during WAN outages. Cisco L2TP support began in IOS 12.0(23) T, but the goal is use an IOS level that supports the features of the standard defined in RFC IOS levels are highly dependent on the platform being used. Be sure to use an IOS that supports L2TPv3 and not L2TP. Router redundancy such as VRRP, HSRP or other is desirable but optional. The goal is to provide routing off the SES subnet during a WAN failure. See diagram on section 7. This is optional. Trunks between the L2 switch and the un-numbered router interface may be desirable to pass non-ses data through the Pseudowire. Broadcasts from these non-ses VLANs will be filtered allowing only unicast data to flow. See diagram on section 7. This is optional. 10) Related Documents Installing, Administering, Maintaining, and Troubleshooting SIP Enablement Services, Doc ID: 03_ BH and MJK 11