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Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
Resilient WAN connections using low cost xDSL circuits
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Resilient WAN connections using low cost xDSL circuits

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This presentation describes the use of low cost adsl and sdsl links to provide backup connection to a primary Janet circuit

This presentation describes the use of low cost adsl and sdsl links to provide backup connection to a primary Janet circuit

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  • 1. Resilient WAN connections
    • The use of redundant xDSL circuits to provide resilient Internet connections.
    • RSC National Technical Forum Nov 2006
    John Potter and Yu King Lau
  • 2. Resilient WAN connections
    • RSC-SE approached in 2005 to provide advice on WAN resiliency.
    • In particular, email was identified as a critical business function following a protracted outage on the college Janet connection
    John Potter and Yu King Lau
  • 3. Resilient WAN connections
    • Desirable features:-
    • Incoming email and limited web connectivity.
    • Low cost (both initial and ongoing).
    • Automatic failover if possible.
    • Bandwidth to be used during normal operation.
    • Independent circuit to maximise redundancy.
    John Potter and Yu King Lau
  • 4. Resilient WAN connections
    • Possible solutions:-
    • Second UKERNA connection ( á la OU)
    • Dual homed UKERNA and DSL (BGP)
    • UKERNA and DSL using RIP
    • Stub connection using MX records and ‘administrative distance’ commands
    John Potter and Yu King Lau
  • 5. Resilient WAN connections
    • The problems can be summarised by function:
    • Incoming mail is handled by multiple MX records in the college DNS entries. Trivial using JANET secondary DNS service. Port forwarding passes DSL mail traffic to email server.
    • Outgoing mail requires that the default gateway configured in the mail server remain valid after a failure of the JANET connection.
    • Web access. Again the default gateway in the proxy server must remain valid after failure.
    John Potter and Yu King Lau
  • 6. Resilient WAN connections
    • The default gateway problem can be resolved in two ways:-
    • Reconfigure each device that uses a default gateway to point to the DSL gateway in the event of failure.
    • Point the default gateway to a device that can automatically update its own default routing information.
    John Potter and Yu King Lau
  • 7. Resilient WAN connections John Potter and Yu King Lau Cisco router Janet Circuit xDSL circuit College LAN aaa.bbb.ccc.dde 195.194.76.58 212.219.90.241 Mail Server Proxy Server 195.194.76.57 aaa.bbb.ccc.ddd Firewall 212.219.90.242
  • 8. Resilient WAN connections
    • One port of the JANET router is connected to the DSL circuit and assigned the appropriate IP address. Additionally, the following static routes would be added to the router configuration:-
    • ip route 0.0.0.0 0.0.0.0 195.184.76.57
    • ip route 0.0.0.0 0.0.0.0 aaa.bbb.ccc.dde 100
    • The ‘100’ parameter is the ‘administrative distance’ and used to determine the ‘cost’ of using that route. This would typically specify an on-demand circuit such as ISDN to be used if the main route failed.
    John Potter and Yu King Lau
  • 9. Resilient WAN connections
    • The next problem is inbound packets. If outbound traffic has been routed via the DSL circuit there is no return path for the packets. The static route entries in the core RNO/UKERNA routers will route the incoming packets through the failed circuit. We can use Network Address Translation to ensure that outgoing packets have a source address of aaa.bbb.ccc.ddd (the Cisco DSL interface). Return packets will then be correctly routed via the DSL circuit.
    • The following Cisco IOS command should enable NAT on the DSL interface:-
    • Ip nat inside source static 212.219.90.241 aaa.bbb.ccc.ddd
    John Potter and Yu King Lau
  • 10. Resilient WAN connections
    • Using the DSL link during normal operation:-
    • Load balancing not appropriate due to contention on DSL line
    • Additional bandwidth can be used for non-critical applications
    • Social area wireless access is ideal application
    John Potter and Yu King Lau
  • 11. Resilient WAN connections John Potter and Yu King Lau Cisco router Janet Circuit xDSL circuit College LAN aaa.bbb.ccc.dde 195.194.76.58 212.219.90.241 Mail Server Proxy Server 195.194.76.57 aaa.bbb.ccc.ddd Firewall 212.219.90.242 Proxy/Content filter Web only access point
  • 12. Resilient WAN connections
    • System was demonstrated in summer 2006
    • Automatic email failover worked as expected
    • Web access could not be tested due to 3 rd party management of college firewall
    • Wireless web access was not implemented
    • Interest from other colleges
    John Potter and Yu King Lau

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