Member Avatar for rkruz

How can one configure a LAN to have redundant links to a single NIC or MAC address? This would be called fault tolerant so that if one link failed the other link would still provide data. The flow would be 2 - 100BaseT links from a server to router/switch for 2 links to router/switch and to a single NIC/IP address.

Would duplicate data be sent on each link and the receiver somehow select one or would the router reconverge to the redundant link by sensing a link failure and reconverging to the backup link?

Any thoughts or literature you might refer me to so that I could understand how to do this or if it can be done?

Thanks for any tips

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  • Latest Post Latest Post by chris5126

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Short answer: there are two practical models to get a single IP/MAC to survive a cable or port failure — make the two wires act as one logical interface so both can carry traffic, or keep one active and fail over to the other at the host. Duplicate frames are not normally sent on both links; instead the bundle or the host decides which link carries each packet and reconverges when a link dies.

Given the Nortel 8600 and Solaris (as described) the choice comes down to goals. If you need combined throughput and transparent failover for existing TCP sessions, use a switch-and-host bundling solution that presents one logical interface to the server and to the switch (both ends must support the same aggregation behavior). If you only need fault tolerance (not aggregated bandwidth) and want simpler switch config, use host-managed failover: the server keeps one active port and moves the address to the other port on failure. pointed at both approaches; the practical tradeoffs are bandwidth vs simplicity and whether you can span two physical switches without special multi-chassis features.

Quick validation and troubleshooting checklist:

  • Confirm negotiated speed/duplex and MTU match on both ends before bundling.
  • Verify MAC learning on the switch (watch the CAM table) during a failover to ensure the switch learns the server MAC on the new port.
  • Simulate failure with an unplug or admin shutdown while running a long TCP transfer (iperf or similar) and capture traffic (tcpdump) to see whether sessions survive and whether duplicate frames appear.
  • Check driver/firmware and switch logs for LACP/aggregation or link-flap messages; mismatched LACP mode, STP blocking or driver limitations are common failure points.

Cautions: do not connect the two server cables to separate, independent switches unless the switches support multi-chassis aggregation — otherwise STP or MAC learning will cause blocked ports or blackholed traffic. If absolute zero-packet-loss is required, add application-level redundancy or clustering rather than relying solely on link failover.

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Member Avatar for chris5126

you can do this a number of ways. SMLT (split multi link trunking) IPMP (IP multi pathing) etc etc but first you should tell us what software and hardware your using as some o/s e.g sun support IPMP in software and most routers will support (SMLT) in hardware or you can use both hardware and software!!

Member Avatar for rkruz

Nortel 8600 router/switches. We cant really have with the host software but the OS is solaris. We are putting in a network manager on a separate PC using windows.

Member Avatar for chris5126

Well solaris supports both IPMP and link aggrigation and they do it very well i know the nortel 8600 supports the link aggrigation so would def suggest that. The command you need to look at is dladm the man page or sun solve documents are very useful

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