SitePathMTPX

Some of my SitePaths won't work even if the configuration is good, the GMACs are up, and I can ping from one side to the other

This is normally because some of your internet infrastructure is redundant. If you have routers configured in HSRP the packets received from the router will have the source MAC of the physical interface of the router, but your GMAC is defined with the virtual MAC. To solve this problem use the gmac disc command with the real IP address of both routers to find the MAC address of each interface. Then add these MAC to your GMAC with the gmac alias command.

What are the different algorithms available with SitePathMTPX?

Four algorithms are available:

• Weight First Algorithm (WFA)
• Best Sitepath First Algorithm (BSFA)
• Roundtime Trip First Algorithm (RTFA)
• Multiplexing (MTPX)

All those algorithms ensure failover and resiliency for the best point to point uptime between your sites.
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WFA: The Weight First Algorithm will look at the weights you have assigned to each path, only a path down will make the Link Balancer change the current chosen path.

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BSFA: The Best Sitepath First Algorithm has been developed to always prefer the BEST path available. The objective is to use the path with the most available bandwidth.

The default metric calculation for each path is:

• Effective outbound bandwidth : 40%
• Current RTT : 20%
• Average RTT : 10%
• Packet Loss : 20%
• SitePath weight : 10%

The effective outbound bandwidth for a path is the minimum value between the local outgoing available bandwidth and the remote incoming available bandwidth.

For a total of 100% of the metric value. Those percentages can be personalized to your preferences, you could, for example, decide that BSFA will only take the RTT along with the packet loss for the metric value. This can be tweaked using the "spath group calibrate" command. Should a new best path be calculated it will need to be at least 20% better (in metric value) before the Link LB will actually move the traffic over the new Best SitePath.

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RTFA: The Roundtime Trip First Algorithm objective is that packets reach destination using the fastest path (based on RTT)

RTFA algorithm can be used to pass traffic that has a very low tolerance to latency, such as VoIP. This algorithm will ensure that the fastest path will always be used. As opposed to BSFA, there is no pre-condition for changing the currently used SitePath other than the metric recalculation. As soon as a new best path is discovered, the traffic is switched on this new path. In effect this gives a load-sharing effect when links of comparable nature and speed are used. When the load increases on the currently used link, its RTT will naturally increase while the idle link will remain at the original RTT, the Link LB will then switch the traffic on the now lower RTT link.

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MTPX: Multiplexing

The MTPX algorithm is the only one that can do path bonding. The decision to use multiple paths at the same time is taken and re-evaluated constantly by the Link LB to ensure the best possible performance. To ensure that the data packets transited trough the SitePath will reach the other end in a timely and orderly fashion the RTT and available bandwidth of each path is calculated by both Link LBs. Should one path slow down too much then it is automatically taken out of the SitePath multiplexing.

Can SitePathMTPX work with links that do not have static IPs?

Yes, SitePathMTPX is compatible with DHCP or PPPoE links. In order for each Link LB to be able to find and identify other sites you need at least one static IP per site among the available links.